Update: 27-Aug-2010

Title:
Effect of Mg-based spherical quasicrystal on microstructures and mechanical properties of ZA54 alloy
Authors:
Zhang, JS; Zhang, YQ; Zhang, Y; Xu, CX; Wang, XM; Yan, J Author Full Names: Zhang Jin-shan; Zhang Yong-qing; Zhang Yan; Xu Chun-xiang; Wang Xiao-ming; Yan Jie
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA 20 (7): 1199-1204 JUL 2010
Abstract:
To improve the strength, toughness and heat-resistance of magnesium alloy, the microstructure and mechanical properties of ZA54 alloy reinforced by icosahedral quasicrystal phase (I-phase) particles were studied. Except alpha-Mg, phi-phase and tau-phase, MgZnYMn I-phase particles can be obtained in ZA54-based composites by the addition of icosahedral quasicrystal-contained Mg-Zn-Y-Mn master alloy. The introduction of MgZnYMn I-phase into ZA54 alloy has great contribution to the refinement of matrix microstructures and the improvement of mechanical properties. When the addition of Mg-based spherical quasicrystal master alloy is up to 3.5% (mass fraction), the macro-hardness of ZA54-based composites is increased to HB 68. The impact toughness of composites reaches the peak value of 18.3 J/cm(2), which is about 29% higher than that of ZA54 mother alloy. The highest tensile properties at ambient and elevated temperatures with master alloy addition of 2.5% (473 K) are also obtained in ZA54-based composites with 3.5% (mass fraction) Mg-Zn-Y-Mn master alloy addition. The ultimate tensile strength of composites at ambient and elevated temperatures are 192.5 MPa and 174 MPa, which are 23.4% and 33.8% higher than that of ZA54 mother alloy, respectively. The improved mechanical properties are mainly attributed to the pinning effect of I-phase on grain boundaries.
Title:
Magnetic field and temperature dependence of the amplitude-modulated magnetic structure of PrNi2Si2 determined by single-crystal neutron diffraction
Authors:
Blanco, JA; Fak, B; Ressouche, E; Grenier, B; Rotter, M; Schmitt, D; Rodriguez-Velamazan, JA; Campo, J; Lejay, P Author Full Names: Blanco, J. A.; Fak, B.; Ressouche, E.; Grenier, B.; Rotter, M.; Schmitt, D.; Rodriguez-Velamazan, J. A.; Campo, J.; Lejay, P.
Source:
PHYSICAL REVIEW B 82 (5): Art. No. 054414 AUG 11 2010
Abstract:
The temperature and magnetic field dependence of the magnetic structure in the singlet crystal-field ground-state system PrNi2Si2 have been determined using single-crystal neutron diffraction. At the magnetic ordering temperature in zero field, T-N=20.0 +/- 0.5 K, an amplitude-modulated magnetic structure sets in with a propagation vector k=(0, 0, 0.87) and the magnetic moments of the Pr3+ ions parallel to the c axis of the body-centered tetragonal structure. The magnetic structure remains amplitude modulated down to low temperatures (T=1.6 K) with only a small tendency to squaring up, as signaled by the weak intensity of the third harmonic that develops below 16 K. With applied field along the easy axis, the modulated structure goes smoothly over into a ferromagnetic state. At the critical field of H-c=58 kOe, the first harmonic disappears and the field-induced ferromagnetic moment shows a kink, in agreement with magnetization measurements. Both the temperature and magnetic field dependence are well described by a periodic field Hamiltonian including magnetic exchange and the crystalline electric field.
Title:
Quasiperiodic Pb monolayer on the fivefold i-Al-Pd-Mn surface: Structure and electronic properties
Authors:
Krajci, M; Hafner, J; Ledieu, J; Fournee, V; McGrath, R Author Full Names: Krajci, M.; Hafner, J.; Ledieu, J.; Fournee, V.; McGrath, R.
Source:
PHYSICAL REVIEW B 82 (8): Art. No. 085417 AUG 11 2010
Abstract:
Lead is one of few elements that adopts a pseudomorphic structure when deposited on quasicrystalline substrates. We present a structural model of quasiperiodic Pb overlayers formed on the fivefold surface of an icosahedral A1-Pd-Mn quasicrystal at two different coverages close to saturation. The skeleton of the Pb monolayer is formed by a network of "starfish" (SF) clusters formed at the initial stages of Pb deposition, as studied in detail in our previous work [Ledieu et al., Phys. Rev. B 79, 165430 (2009)]. The atomic structure of the Pb monolayers can be represented as a decorated pentagonal Penrose P1 tiling. The structural models reproduce also the quasiperiodic superstructure of the layers observed in experimental scanning tunneling microscopy (STM) images which is described by the tau-scaled tau P1 tiling (tau is the golden mean). The atomic structure underlying the observed tau-scaled "white flower" motifs and the origin of irregular bright spots in STM! images are discussed. The bright spots appear in the centers of the SF clusters centered at substrate sites occupied by A1 atoms. The calculated electronic structure shows that the minimum in the density of states (pseudogap) at the Fermi level which is characteristic for the A1-Pd-Mn quasicrystals appears also in the local density of states of the adsorbed Pb monolayer. However, our analysis demonstrates that the formation of this pseudogap is not due to the quasiperiodic arrangement of the Pb atoms but to the strong hybridization of their orbitals with the substrate.
Title:
Structure and reactivity of Bi allotropes on the fivefold icosahedral Al-Pd-Mn quasicrystal surface
Authors:
Smerdon, JA; Cross, N; Dhanak, VR; Sharma, HR; Young, KM; Lograsso, TA; Ross, AR; McGrath, R Author Full Names: Smerdon, J. A.; Cross, N.; Dhanak, V. R.; Sharma, H. R.; Young, K. M.; Lograsso, T. A.; Ross, A. R.; McGrath, R.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (34): Art. No. 345002 SEP 1 2010
Abstract:
The growth of Bi on a pseudomorphic Bi monolayer on the fivefold surface of the icosahedral Al-Pd-Mn quasicrystal has been investigated using low energy electron diffraction and scanning tunnelling microscopy. Initially randomly oriented pseudocubic islands are formed with a preference for an even number of layers. Subsequently a morphological transformation takes place to hexagonal Bi islands, which align along high symmetry directions of the substrate. The Bi flux is found to have a strong effect on which island structure is preferred. When C-60 is adsorbed on the three different allotropes of Bi present in this system, hexagonal C-60 islands are formed in each case. On the pseudocubic and hexagonal islands, the C-60 islands are aligned with the substrate. We discuss the energetic, kinetic and geometrical factors which influence the morphological transformation referred to above.
Title:
Activated impurity states in the incommensurate phase of ferroelectric semiconductor TlInS2
Authors:
Seyidov, MY; Suleymanov, RA; Salehli, F Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Salehli, Ferid
Source:
JOURNAL OF APPLIED PHYSICS 108 (2): Art. No. 024111 JUL 15 2010
Abstract:
The effect of annealing within the incommensurate phase on the dielectric function epsilon of the TlInS2 single crystals has been investigated. It is shown that the effect of annealing is very close to the effect of doping by electrically active impurity La. The inference is made that the correlation between observed effects in annealed and doped crystals is conditioned by the internal electric fields induced by the activation (polarization) of native defects during the annealing procedure. The investigations of the Second harmonic generation in undoped TlInS2 crystal and the pyrocurrent in TlInS2 : La confirms the proposed model. (C) 2010 American Institute of Physics. [doi:10.1063/1.3466764]
Title:
Magnetic ordering in PrT2Ge2 (T = Ni, Ru and Rh) compounds
Authors:
Szytula, A; Kaczorowski, D; Gondek, L; Pikul, A; Arulraj, A; Balanda, M; Baran, S; Penc, B Author Full Names: Szytula, A.; Kaczorowski, D.; Gondek, L.; Pikul, A.; Arulraj, A.; Balanda, M.; Baran, S.; Penc, B.
Source:
INTERMETALLICS 18 (9): 1766-1771 SEP 2010
Abstract:
X-ray and neutron diffraction, magnetization, magnetic susceptibility and electrical resistivity measurements were performed on polycrystalline samples of PrNi2Ge2, PrRu2Ge2 and PrRh2Ge2. All the investigated compounds crystallize with a tetragonal structure of the ThCr2Si2-type. All of them exhibit metallic-like electrical conductivity and order magnetically at low temperatures, namely PrNi2Ge2 and PrRh2Ge2 are antiferromagnetic below T-N = 23.5 and 45 K, respectively, while PrRu2Ge2 is a ferromagnet with T-C = 14.8 K. The neutron diffraction data indicated a modulated antiferromagnetic structure in PrNi2Ge2 in the entire ordered region. For PrRh2Ge2 a collinear antiferromagnetic ordering was derived below T-t = 30 K and a sine-modulated ordering above that temperature. The neutron diffraction corroborated a simple ferromagnetic structure in PrRu2Ge2. (C) 2010 Elsevier Ltd. All rights reserved.

Update: 20-Aug-2010

Title:
Sound behavior near the Lifshitz point in proper ferroelectrics
Authors:
Kohutych, A; Yevych, R; Perechinskii, S; Samulionis, V; Banys, J; Vysochanskii, Y Author Full Names: Kohutych, A.; Yevych, R.; Perechinskii, S.; Samulionis, V.; Banys, J.; Vysochanskii, Yu.
Source:
PHYSICAL REVIEW B 82 (5): Art. No. 054101 AUG 4 2010
Abstract:
The interaction between soft optic and acoustic phonons was investigated for Sn2P2(Se0.28S0.72)(6) proper uniaxial ferroelectrics by Brillouin-scattering and ultrasonic pulse-echo techniques. The elastic softening of hypersound velocity of transverse-acoustic phonons and for both longitudinal and transverse ultrasound waves which propagate near direction of the modulation wave vector (in the incommensurate phase at x > x(LP)) was found at cooling to the Lifshitz point in the paraelectric phase. The strong increase in the ultrasound attenuation has also been observed. Such phenomena are related to the linear interaction of the soft optic and acoustic branches in the region of relatively short-range hypersound waves and to the strongly developed long-range order-parameter fluctuations in the ultrasound frequency range. The hypersound velocity temperature dependence was described within the Landau-Khalatnikov approximation for the ferroelectric phase.
Title:
Time relaxation of permittivity in [(CH3)2NH2]3CuCl5 crystal under external electric field
Authors:
Eliyashevskyy, Y; Czapla, Z; Dacko, S Author Full Names: Eliyashevskyy, Yu.; Czapla, Z.; Dacko, S.
Source:
PHASE TRANSITIONS 83 (8): 564-571 2010
Abstract:
Continuation of our previous studies connected with dielectric properties of tris-dimethylammoniumpentachlorocuprate crystal [(CH3)2NH2]3CuCl5 crystal under the influence of electric field are presented in this article. We studied the time dependence of the permittivity under the influence of electric field at constant temperatures above Tc. In experiment, slow but significant decrease of permittivity was observed, which can be described with two main relaxation processes. The observed dielectric behavior can be related to the coexistence of phases and slow transition to ferroelectric one through long-time metastable states connected with the presence of incommensurate phase in the studied crystal. The coexistence of phases and slow transition was confirmed from the appearance of induced polarization under external electric field, measured as depolarization current.
Title:
The local structure and composition of Ba4Nb2O9-based oxycarbonates
Authors:
Bezjak, J; Abakumov, AM; Recnik, A; Krzmanc, MM; Jancar, B; Suvorov, D Author Full Names: Bezjak, Jana; Abakumov, Artem M.; Recnik, Aleksander; Krzmanc, Marjeta Macek; Jancar, Bostjan; Suvorov, Danilo
Source:
JOURNAL OF SOLID STATE CHEMISTRY 183 (8): 1823-1828 AUG 2010
Abstract:
X-ray powder-diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), infrared spectroscopy (IR), thermogravimetry (TG) and mass spectroscopy (MS) were performed to investigate the composition and the crystal structure of tetra-barium di-niobate (V) Ba4Nb2O9. The TG, MS and IR studies revealed that the compound is a hydrated oxycarbonate. Assuming that the carbonate stoichiometrically replaces oxygen, the composition of the low-temperature alpha-modification, obtained by slow cooling from 1100 degrees C, corresponds to Ba4Nb2O8.8(CO3)(0.2)center dot 0.1H(2)O, while the quenched high-temperature gamma-modification has the Ba4Nb2O8.42(CO3)(0.58)center dot 0.38H(2)O composition. The alpha-phase has a composite incommensurately modulated structure consisting of two mutually interacting [Ba](infinity) and the [(Nb, square)O-3](infinity) subsystems. The composite modulated crystal structure of the alpha-phase can be described with the lattice parameters a=10.2688(1) angstrom, c=2.82426(8) angstrom, q=0.66774(2)c* and a superspace group R (3) over barm(00 gamma)0s. The HRTEM analysis demonstrates the nanoscale twinning of the trigonal domains parallel to the {1 0 0} crystallographic planes. The twinning introduces a one-dimensional disorder into the [(Nb, square(3)](infinity) subsystem, which results in an average P (6) over bar 2c crystal structure of the alpha-phase. Possible places for the carbonate group in the structure are discussed using a comparison with other hexagonal perovskite-based oxycarbonates. (C) 2010 Elsevier Inc. All rights reserved.
Title:
Magnetic structure of ErCu2Ge2
Authors:
Penc, B; Baran, S; Kaczorowski, D; Hoser, A; Szytula, A Author Full Names: Penc, B.; Baran, S.; Kaczorowski, D.; Hoser, A.; Szytula, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 503 (1): L18-L20 JUL 30 2010
Abstract:
The compound ErCu2Ge2 which crystallizes in the tetragonal ThCr2Si2-type crystal structure orders antiferromagnetically at low temperatures. At 1.4 K, the Er magnetic moments are arranged in a commensurate structure described by the propagation vector (k) over right arrow = [1/2, 0, 1/2]. The magnetic moment is equal to 6.80(7) mu(B) and forms an angle of 27 degrees with the c-axis. At T-t = 2.6 K an additional incommensurate magnetic structure appears and at higher temperatures both structures coexist and concurrently disappear at T-N = 3.1 K. The magnetic phase transitions at T-t and T-N clearly manifest themselves in the heat capacity and thermal expansion data of the compound. (C) 2010 Elsevier B.V. All rights reserved.

Update: 13-Aug-2010

Title:
Coexistence and Competition of Magnetism and Superconductivity on the Nanometer Scale in Underdoped BaFe1.89Co0.11As2
Authors:
Marsik, P; Kim, KW; Dubroka, A; Roessle, M; Malik, VK; Schulz, L; Wang, CN; Niedermayer, C; Drew, AJ; Willis, M; Wolf, T; Bernhard, C Author Full Names: Marsik, P.; Kim, K. W.; Dubroka, A.; Roessle, M.; Malik, V. K.; Schulz, L.; Wang, C. N.; Niedermayer, Ch.; Drew, A. J.; Willis, M.; Wolf, T.; Bernhard, C.
Source:
PHYSICAL REVIEW LETTERS 105 (5): Art. No. 057001 JUL 27 2010
Abstract:
We report muon spin rotation (mu SR) and infrared spectroscopy experiments on underdoped BaFe1.89Co0.11As2 which show that bulk magnetism and superconductivity (SC) coexist and compete on the nanometer length scale. Our combined data reveal a bulk magnetic order, likely due to an incommensurate spin density wave (SDW), which develops below T-mag approximate to 32 K and becomes reduced in magnitude (but not in volume) below T-c = 21.7 K. A slowly fluctuating precursor of the SDW seems to develop already below the structural transition at T-s approximate to 50 K. The bulk nature of SC is established by the mu SR data which show a bulk SC vortex lattice and the IR data which reveal that the majority of low-energy states is gapped and participates in the condensate at T << T-c.
Title:
Synthesis of Ti-Zr-Ni amorphous and quasicrystal powders by mechanical alloying, and their electrochemical properties
Authors:
Takasaki, A; Okuyama, T; Szmyd, JS Author Full Names: Takasaki, Akito; Okuyama, Tetsuya; Szmyd, Janusz S.
Source:
JOURNAL OF MATERIALS RESEARCH 25 (8): 1575-1582 AUG 2010
Abstract:
Mechanical alloying of Ti45Zr38-xNi17+x and Ti45-xZr38Ni17+x (0 <= x <= 8) elemental powders produced an amorphous phase, but subsequent annealing converted the amorphous phase into an icosahedral quasicrystal phase, along with a Ti2Ni-type phase. The discharge capacities, measured in a three-electrode cell at room temperature for both the amorphous and quasicrystal electrodes, increased with increasing Ni substitution for Zr or Ti. The highest discharge capacities, which were about 60 mAh/g for the amorphous electrode and 100 mAh/g for the quasicrystal electrode, were obtained from (Ti45Zr30Ni25) after substitution of Ni for Zr. For the Ti45Zr30Ni25 composition, the discharge performance of the quasicrystal electrode was stable over charge/discharge cycling, but that of the amorphous electrode gradually decreased with cycling. The structure of the quasicrystal phase in the electrodes was stable, even after 15 charge/discharge cycles, but the amorphous phase converted to a (Ti, Zr)H-2 f.c.c. hydride.
Title:
Relation between glass and quasicrystal formation in the Zr-Nb-Cu-Ni-Al alloys upon solidification
Authors:
Zhu, ZW; Zhang, W; Xie, GQ; Inoue, A Author Full Names: Zhu, Zhengwang; Zhang, Wei; Xie, Guoqiang; Inoue, Akihisa
Source:
APPLIED PHYSICS LETTERS 97 (3): Art. No. 031919 JUL 19 2010
Abstract:
We reported the relationship among the icosahedral short-range order (ISRO), glass formation and quasicrystal formation in the Zr-Nb-Cu-Ni-Al alloys. The alloys with the Nb addition stabilized ISRO, making the alloys form the amorphous, quasicrystal and crystal with decreasing the cooling rate. Not only bulk glass but also bulk quasicrystal were found to form for these alloys. The structural evolution from the amorphous phase, to the quasicrystal and crystals with the variation in the Nb content or the cooling rate is present. These findings were related to the degree of ISRO, which are advantageous for understanding the glass formation phenomenon. (C) 2010 American Institute of Physics. [doi:10.1063/1.3467827]

Update: 6-Aug-2010

Title:
Phase separation and ferroelectric ordering in charge-frustrated LuFe2O4-delta
Authors:
Yang, HX; Tian, HF; Zhang, Y; Qin, YB; Zeng, LJ; Ma, C; Shi, HL; Lu, JB Author Full Names: Yang, H. X.; Tian, H. F.; Zhang, Y.; Qin, Y. B.; Zeng, L. J.; Ma, C.; Shi, H. L.; Lu, J. B.
Source:
SOLID STATE COMMUNICATIONS 150 (31-32): 1467-1472 AUG 2010
Abstract:
The transmission electron microscopy observations of the charge ordering (CO) which governs the electronic polarization in LuFe2O4-delta clearly show the presence of a remarkable phase separation at low temperatures. Two CO ground states are found to adopt the charge modulations of Q(1) = (1/3, 1/3, 0) and Q(2) = (1/3 + epsilon, 1/3 + epsilon, 3/2), respectively. Our structural study demonstrates that the incommensurately Q(2)- modulated state is chiefly stable in samples with relatively lower oxygen contents. Data from theoretical simulations of the diffraction suggest that both Q(1)- and Q(2)- modulated phases have ferroelectric ordering. The effects of oxygen concentration on the phase separation and electric polarization in this layered system are discussed. (C) 2010 Elsevier Ltd. All rights reserved.
Title:
Extreme sensitivity of a frustrated quantum magnet: Cs2CuCl4
Authors:
Starykh, OA; Katsura, H; Balents, L Author Full Names: Starykh, Oleg A.; Katsura, Hosho; Balents, Leon
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 014421 JUL 20 2010
Abstract:
We report a thorough theoretical study of the low temperature phase diagram of Cs2CuCl4, a spatially anisotropic spin S = 1/2 triangular lattice antiferromagnet, in a magnetic field. Our results, obtained in a quasi-one-dimensional limit in which the system is regarded as a set of weakly coupled Heisenberg chains, are in excellent agreement with experiment. The analysis reveals some surprising physics. First, we find that when the magnetic field is oriented within the triangular layer, spins are actually most strongly correlated within planes perpendicular to the triangular layers. This is despite the fact that the interlayer exchange coupling in Cs2CuCl4 is about an order of magnitude smaller than the weakest (diagonal) exchange in the triangular planes themselves. Second, the phase diagram in such orientations is exquisitely sensitive to tiny interactions, heretofore neglected, of order a few percent or less of the largest exchange couplings. These interactions, which we describe in detail, induce entirely new phases, and a novel commensurate-incommensurate transition, the signatures of which are identified in NMR experiments. We discuss the differences between the behavior of Cs2CuCl4 and an ideal two-dimensional triangular model, and in particular, the occurrence of magnetization plateaux in the latter. These and other related results are presented here along with a thorough exposition of the theoretical methods, and a discussion of broader experimental consequences to Cs2CuCl4 and other materials.
Title:
Magnetic excitations in Dy/Y superlattices as seen via inelastic neutron scattering
Authors:
Grunwald, ATD; Wildes, AR; Schmidt, W; Tartakovskaya, EV; Kwo, J; Majkrzak, C; Ward, RCC; Schreyer, A Author Full Names: Gruenwald, A. T. D.; Wildes, A. R.; Schmidt, W.; Tartakovskaya, E. V.; Kwo, J.; Majkrzak, C.; Ward, R. C. C.; Schreyer, A.
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 014426 JUL 23 2010
Abstract:
Measurements of the spin excitations propagating normal to the interfaces in Dy/Y superlattices using neutron inelastic scattering are presented. For a given magnon momentum, a neutron-scattering spectrum shows multiple peaks at different energies, which indicates discrete energy spectra. The results are compared with theoretical calculations developed here to describe magnetic excitations in rare-earth superlattices. The theory accounts for Ruderman-Kittel-Kasuya-Yosida (RKKY) and Dzyaloshinsky-Moriya interactions in incommensurate helicoidal structures and achieves a quantitative agreement with the experimental data. This work demonstrates that neutron inelastic scattering can be used for systematic studies of the exchange interactions and spin dynamics in nanomagnetic systems over wide areas of the Brillouin zone.
Title:
Spatial inhomogeneities in iron pnictide superconductors: The formation of charge stripes
Authors:
Gor'kov, LP; Teitel'baum, GB Author Full Names: Gor'kov, Lev P.; Teitel'baum, Gregory B.
Source:
PHYSICAL REVIEW B 82 (2): Art. No. 020510 JUL 21 2010
Abstract:
The heterogeneous coexistence of antiferromagnetism (spin-density wave (SDW)] and superconductivity on a mesoscopic scale was observed in iron pnictides in many recent experiments. We suggest and discuss the scenario in which the heterogeneity is caused by formation of domain walls inherent to the SDW state of pnictides at a proper doping or under applied pressure. Superconductivity would emerge from the modulated SDW structure. The phenomenon is akin to the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) phase in superconductors.
Title:
Light localization in photonic band gaps of quasiperiodic dielectric structures
Authors:
Wang, K Author Full Names: Wang, Kang
Source:
PHYSICAL REVIEW B 82 (4): Art. No. 045119 JUL 23 2010
Abstract:
Localized light wave states in the photonic band gaps in two-dimensional octagonal and decagonal quasiperiodic dielectric media are investigated by considering the corresponding approximant structures. The structure effects on the local resonances at high-symmetry centers are studied in terms of the interscatterer correlation and the coupling strength between neighbor scatterers is analyzed as a function of the local symmetry order, the structure dielectric contrast, and the scatterer size. It is shown that an interscatterer distance threshold can be defined for the light localization regime. The threshold is determined by the geometrical and dielectric properties of the scatterers and independent of the local symmetry. It is thus likely a universal parameter for light localization in dielectric structures containing high-symmetry centers.
Title:
Symmetry and magnetoelectric interactions in BaMnF4
Authors:
Zvezdin, AK; Pyatakov, AP Author Full Names: Zvezdin, A. K.; Pyatakov, A. P.
Source:
LOW TEMPERATURE PHYSICS 36 (6): 532-537 JUN 2010
Abstract:
Symmetry analysis is used to study magnetic anisotropy and magnetoelectric interactions in the ferroelectric antiferromagnet BaMnF4 theoretically. It is shown that symmetry admits the existence in this material of a nonuniform magnetoelectric interaction (flexomagnetoelectric type) with a specific dependence on the magnitude and orientation of the external magnetic field. With increasing magnetic field this interaction can cause a phase transition into a magnetic incommensurate phase with a characteristic jump of the electric polarization. The linear and quadratic magnetoelectric effects and the question of the relativistic canting of the sublattices, which is due to the magnetoelectric interaction, are examined. The proposed approach is a natural generalization of the method of constructing invariants from the magnetic modes of the crystal to the case of phase transitions with a doubled unit cell of the crystal and can be used for symmetry analysis of other ferroelectric magnetic compounds. (c) 2010 American Institute of Physics. [doi:10.1063/1.3455798]
Title:
Quasicrystalline Tenfold Symmetry Order in Boron Compounds
Authors:
Miyazaki, Y; Okada, J; Abe, E; Yokoyama, Y; Kimura, K Author Full Names: Miyazaki, Yoshinobu; Okada, Junpei; Abe, Eiji; Yokoyama, Yoshihiko; Kimura, Kaoru
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (7): Art. No. 073601 JUL 2010
Abstract:
We report the first quasicrystalline boride formed in a rapidly-solidified B40Ti12Ru48 alloy, whose diffraction pattern clearly reveals a tenfold rotation axis of decagonal symmetry. The local structure appears to be significantly deviated from an ideal quasicrystal, but the long-range bond-orientational-order restricted by linkages between the robust unit-clusters has successfully generated the apparent 10-fold-symmetric Bragg peaks. This may be attributed to an extreme case of random-tiling quasicrystals, which enable the occurrence of local tiling disorders to account for entropy.
Title:
High-Temperature Multiferroic State of RBaCuFeO5 (R = Y, Lu, and Tm)
Authors:
Kawamura, Y; Kai, T; Satomi, E; Yasui, Y; Kobayashi, Y; Sato, M; Kakurai, K Author Full Names: Kawamura, Yuji; Kai, Takahiro; Satomi, Erika; Yasui, Yukio; Kobayashi, Yoshiaki; Sato, Masatoshi; Kakurai, Kazuhisa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (7): Art. No. 073705 JUL 2010
Abstract:
Magnetic and/or dielectric/ferroelectric behaviors have been studied for YBaCuFeO5, LuBaCuFeO5, and TmBaCuFeO5, which are members of oxygen-deficient ordered perovskite systems RBaCuFeO5 (R = lanthanide Ln and other trivalent elements) and have two magnetic transitions. The magnetic structure of the high-temperature (T) ordered phase is basically antiferromagnetic, and in the low-T ordered phase, a modulated magnetic component is superposed on the antiferromagnetic moments. The results of the pyrocurrent measurements indicate that electric polarization is induced in all these systems by the ordering to the modulated magnetic structure. For TmBaCuFeO5, the transition to this low-T phase is found at a temperature as high as the melting point of ice.
Title:
Elastic constants and anisotropic internal frictions of decagonal Al72Ni18Co8 single quasicrystal at low temperatures
Authors:
Tarumi, R; Ledbetter, H; Shiomi, S; Ogi, H; Hirao, M; Tsai, AP Author Full Names: Tarumi, R.; Ledbetter, H.; Shiomi, S.; Ogi, H.; Hirao, M.; Tsai, A. P.
Source:
JOURNAL OF APPLIED PHYSICS 108 (1): Art. No. 013514 JUL 2010
Abstract:
We studied the complete set of elastic constants C-ij and internal frictions tensor Q(ij)(-1) of anisotropic decagonal Al72Ni18Co8 single quasicrystal by electromagnetic acoustic resonance at low temperatures, to 5 K. Most C-ij(T) showed usual stiffening upon cooling and their temperature behaviors are well characterized by an Einstein-lattice-vibration model. The average Gruumlneisen parameter estimated from the bulk modulus is 2.4, almost identical to crystalline Al. Ambient temperature Q(ij)(-1) show a linear relationship to the elastic-constants temperature derivatives vertical bar dC(ij)/dT vertical bar/C-ij with a slope of 1.28 K-1, suggesting that lattice anharmonicity plays a dominant role for Q(ij)(-1). The longitudinal modulus for the decagonal axis C-33 and corresponding internal friction Q(33)(-1), however, showed significant deviation from such ideal behavior, suggesting additional low-frequency phonon-excitation modes along the decagonal axis.
Title:
Layers of order - the past, present and future of superspace crystallography
Authors:
Christensen, J Author Full Names: Christensen, Jeppe
Source:
CRYSTALLOGRAPHY REVIEWS 16 (2): 105-114 2010
Abstract:
The importance of having correct structural descriptions is becoming ever clearer, not only in drug discovery research, but also in the development of new advanced materials. Here the key to optimizing properties lies in understanding the structure-property relationships. Without a correct description theoretical calculations will inevitably fail to describe and explain any experimental observations. With increasing complexity of developed materials, modulated structures are likely to make up an increasing proportion of the structures to be investigated in the future. To take up this challenge, a development is needed in three areas of crystallography: The way we teach and what we teach our students; how we think about, and perform our crystallographic investigations; what tools are available, and how we use them. These areas are strongly coupled and any development in one is dependent on progress in the other two.

Update: 30-Jul-2010

Title:
Atomic dynamics of the alpha-(Al,Si)CuFe alloy: A crystalline approximant of a quasicrystal...
Authors:
Parshin, PP; Zemlyanov, MG; Brand, RA; Pavlyuchkov, D; Ollivier, J Author Full Names: Parshin, P. P.; Zemlyanov, M. G.; Brand, R. A.; Pavlyuchkov, D.; Ollivier, J.
Source:
PHYSICS OF THE SOLID STATE 52 (7): 1492-1498 JUL 2010
Abstract:
The atomic dynamics of the Al0.550Si0.070Cu0.255Fe0.125 alloy with the structure that approximates the structure of an icosahedral quasicrystal with a similar chemical composition has been investigated using inelastic neutron scattering. The partial vibrational spectra of copper, iron, and aluminum atoms and the total spectrum of thermal vibrations of the compound have been directly reconstructed from the experimental data for the first time. A combined analysis of the results obtained and the data on the atomic dynamics of the i-AlCuFe icosahedral quasicrystal has been performed.
Title:
Incommensurate Magnetic Order and Dynamics Induced by Spinless Impurities in YBa2Cu3O6.6
Authors:
Suchaneck, A; Hinkov, V; Haug, D; Schulz, L; Bernhard, C; Ivanov, A; Hradil, K; Lin, CT; Bourges, P; Keimer, B; Sidis, Y Author Full Names: Suchaneck, A.; Hinkov, V.; Haug, D.; Schulz, L.; Bernhard, C.; Ivanov, A.; Hradil, K.; Lin, C. T.; Bourges, P.; Keimer, B.; Sidis, Y.
Source:
PHYSICAL REVIEW LETTERS 105 (3): Art. No. 037207 JUL 16 2010
Abstract:
We report an inelastic-neutron-scattering and muon-spin-relaxation study of the effect of 2% spinless (Zn) impurities on the magnetic order and dynamics of YBa2Cu3O6.6, an underdoped high-temperature superconductor that exhibits a prominent spin pseudogap in its normal state. Zn substitution induces static magnetic order at low temperatures and triggers a large-scale spectral-weight redistribution from the magnetic resonant mode at 38 meV into uniaxial, incommensurate spin excitations with energies well below the spin pseudogap. These observations indicate a competition between incommensurate magnetic order and superconductivity close to a quantum critical point. Comparison to prior data on La2-xSrxCuO4 suggests that this behavior is universal for the layered copper oxides and analogous to impurity-induced magnetic order in one-dimensional quantum magnets.
Title:
Neutron-Scattering Measurement of Incommensurate Short-Range Order in Single Crystals of the S=1 Triangular Antiferromagnet NiGa2S4
Authors:
Stock, C; Jonas, S; Broholm, C; Nakatsuji, S; Nambu, Y; Onuma, K; Maeno, Y; Chung, JH Author Full Names: Stock, C.; Jonas, S.; Broholm, C.; Nakatsuji, S.; Nambu, Y.; Onuma, K.; Maeno, Y.; Chung, J. -H.
Source:
PHYSICAL REVIEW LETTERS 105 (3): Art. No. 037402 JUL 16 2010
Abstract:
Neutron scattering is used to investigate spin correlations in ultrapure single crystals of the S = 1 triangular lattice NiGa2S4. Despite a Curie-Weiss temperature of Theta(CW) = -80(2) K, static (T > 1 ns) short-range (zeta(ab) = 26(3) angstrom) incommensurate order prevails for T > 1.5 K. The incommensurate modulation Q(0) = (0.155(3), 0.155(3), 0), Theta(CW), and the spin-wave velocity (c = 4400 m/s) can be accounted for by antiferromagnetic third-nearest-neighbor interactions J(3) = 2.8(6) meV and ferromagnetic nearest-neighbor coupling J(1) = -0.35(9) J(3). Interplane correlations are limited to nearest neighbors and weakened by an in-plane field. These observations show that the short-range ordered glassy phase that has been observed in a number of highly degenerate systems can persist near the clean limit.
Title:
Single-crystal neutron diffraction study of the magnetic structure of Er3Co
Authors:
Gubkin, AF; Podlesnyak, A; Baranov, NV Author Full Names: Gubkin, A. F.; Podlesnyak, A.; Baranov, N. V.
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 012403 JUL 13 2010
Abstract:
The effect of the magnetic field applied along the main crystallographic directions on the magnetic structure of Er3Co has been studied by means of single-crystal neutron diffraction technique. At zero field the compound exhibits a noncoplanar commensurate magnetic structure with ferromagnetic alignment of the Er magnetic-moment projections along the b axis in an orthorhombic unit cell. The present measurements revealed that the application of the magnetic field along the c direction [c perpendicular to (ab)] leads to the pronounced metamagneticlike transition in the low-field region mu H-0<1.2 T, although, the magnetization curve does not exhibit any anomalies. Combining the present single-crystal diffraction and magnetization data with the results of the previous powder neutron diffraction study [Gignoux et al., Solid State Commun. 8, 391 (1970)], we conclude that the nature of the magnetic ion, whether Kramers or non-Kramers, has a decisive effect on the commensurability of the magnetic structure of R3Co. In particular, the commensurate magnetic structure observed in Er3Co originate from the Kramers character of Er3+ ion in contrast to the incommensurate structures found earlier in R3Co with R= Tb and Ho.
Title:
Transition from a phase-segregated state to single-phase incommensurate sodium ordering in gamma-NaxCoO2(x approximate to 0.53)
Authors:
Feyerherm, R; Dudzik, E; Valencia, S; Wolter, AUB; Milne, CJ; Landsgesell, S; Alber, D; Argyriou, DN Author Full Names: Feyerherm, R.; Dudzik, E.; Valencia, S.; Wolter, A. U. B.; Milne, C. J.; Landsgesell, S.; Alber, D.; Argyriou, D. N.
Source:
PHYSICAL REVIEW B 82 (2): Art. No. 024103 JUL 13 2010
Abstract:
Synchrotron x-ray diffraction investigations of two single crystals of sodium cobaltate NaxCoO2 from different batches with composition x=0.525-0.530 reveal homogeneous incommensurate sodium ordering with propagation vector (0.53 0.53 0) at room temperature. The incommensurate (qq0) superstructure exists between 220 and 430 K. The value of q varies between q=0.514 and 0.529, showing a broad plateau at the latter value between 260 and 360 K. On cooling, an unusual reversible phase segregation into two volume fractions is observed. Below 220 K, one volume fraction shows the well-known commensurate orthorhombic x=0.50 superstructure while a second volume fraction with x=0.55 exhibits another commensurate superstructure, presumably with a 6a x 6a x c hexagonal supercell. We argue that the commensurate-to-incommensurate transition is an intrinsic feature of samples with Na concentrations x=0.5+ delta with delta approximate to 0.03.

Update: 23-Jul-2010

Title:
Magnetic structure of the edge-sharing copper oxide chain compound NaCu2O2
Authors:
Capogna, L; Reehuis, M; Maljuk, A; Kremer, RK; Ouladdiaf, B; Jansen, M; Keimer, B Author Full Names: Capogna, L.; Reehuis, M.; Maljuk, A.; Kremer, R. K.; Ouladdiaf, B.; Jansen, M.; Keimer, B.
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 014407 JUL 12 2010
Abstract:
Single-crystal neutron diffraction has been used to determine the incommensurate magnetic structure of NaCu2O2, a compound built up of chains of edge-sharing CuO4 plaquettes. Magnetic structures compatible with the lattice symmetry were identified by a group-theoretical analysis and their magnetic structure factors were compared to the experimentally observed Bragg intensities. In conjunction with other experimental data, this analysis yields an elliptical helix structure in which both the helicity and the polarization plane alternate among copper-oxide chains. This magnetic ground state is discussed in the context of the recently reported multiferroic properties of other copper-oxide chain compounds.
Title:
Surface oxidation of the icosahedral Ag-In-Yb quasicrystal
Authors:
Nugent, PJ; Simutis, G; Dhanak, VR; McGrath, R; Shimoda, M; Cui, C; Tsai, AP; Sharma, HR Author Full Names: Nugent, P. J.; Simutis, G.; Dhanak, V. R.; McGrath, R.; Shimoda, M.; Cui, C.; Tsai, A. P.; Sharma, H. R.
Source:
PHYSICAL REVIEW B 82 (1): Art. No. 014201 JUL 9 2010
Abstract:
The oxidation of the high-symmetry surfaces of a single grain icosahedral (i) Ag-In-Yb quasicrystal has been studied using x-ray photoemission spectroscopy. The oxidation was carried out in vacuum, air, and water. It is found that air exposure results in the same degree of oxidation as exposure to oxygen in vacuum. The oxidation in water is more effective. Among the three constituent elements, the core levels of Yb are most affected by oxidation, Ag core levels are unchanged, and In shows moderate effects as expected from heats of formation of bulk oxides of the three elements. The comparison of the results with pure elements also reveals that the oxidation of Ag, In, and Yb in the quasicrystal is very similar to that of pure elements in all three environments. Scanning tunneling microscopy and low-energy electron diffraction reveal that oxidation destroys the quasicrystalline order of the clean surface.
Title:
Structural study by X-ray diffraction and transmission electron microscopy of the misfit compound (SbS1-xSex)(1.16)(Nb1.036S2)(2)
Authors:
Kars, M; Fredrickson, DC; Gomez-Herrero, A; Lidin, S; Rebbah, A; Otero-Diaz, LC Author Full Names: Kars, Mohammed; Fredrickson, Daniel C.; Gomez-Herrero, A.; Lidin, Sven; Rebbah, Allaoua; Otero-Diaz, L. C.
Source:
MATERIALS RESEARCH BULLETIN 45 (8): 982-988 AUG 2010
Abstract:
In the Sb-Nb-S-Se system, a new misfit layer compound (MSL) has been synthesized and its structure was determined by combining single crystal X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. It presents a composite crystal structure formed by (SbS1-xSex)slabs stacking alternately with double NbS2 layers and both can be treated as separate monoclinic subsystems. The (SbS1-xSex) slabs comprise a distorted, two-atom-thick layer with NaCl-type structure formed by an array of (SbX5) square pyramids joined by edges (X: S, Se); the NbS2 layers consist of (SbX5) trigonal prisms linked through edge-sharing to form sheets, just as in the 2H-NbS2 structure type. Both sublattices have the same lattice parameters a = 5.7672(19) angstrom, c = 17.618(6) angstrom and beta = 96.18(3)degrees, with incommensurability occurring along the b direction: b(1) = 3.3442(13) angstrom for the NbS2 subsystem and b(2) = 2.8755(13) angstrom for the (SbS1-xSex) subsystem. The occurrence of diffuse scattering intensity streaked along c* indicates that the (SbS1-xSex) subsystem is subjected to extended defects along the stacking direction. Published by Elsevier Ltd.

Update: 16-Jul-2010

Title:
Magnetic ordering and low-temperature thermodynamic properties of ErFe2Ge2
Authors:
Szytula, A; Kaczorowski, D; Baran, S; Penc, B; Gil, A; Hoser, A Author Full Names: Szytula, A.; Kaczorowski, D.; Baran, S.; Penc, B.; Gil, A.; Hoser, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (19): 2973-2977 OCT 2010
Abstract:
Polycrystalline sample of ErFe2Ge2 was investigated by means of magnetic susceptibility, heat capacity and electrical resistivity measurements, as well as by powder neutron diffraction. All these experiments yielded an evidence of magnetic ordering setting at about 3 K. The low-temperature neutron data revealed the formation of a sine-modulated commensurate antiferromagnetic structure characterized by the propagation vector k=(0, 0, 14). The erbium magnetic moment is aligned parallel to the crystallographic a-axis. At T=1.55 K it is equal to 7.06(5) mu(B). (C) 2010 Elsevier B. V. All rights reserved.
Title:
Pattern analysis and interpretation of scattering from short-range order stacking in the layered composite crystal 2H-NaxCoO2 center dot yD(2)O (x similar or equal to 0.35, y similar or equal to 1.3)
Authors:
Onoda, M; Takada, K; Sasaki, T Author Full Names: Onoda, Mitsuko; Takada, Kazunori; Sasaki, Takayoshi
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 677-685 Part 4 AUG 2010
Abstract:
Information about the features of Bragg reflections and/or diffuse streaks was obtained through simulation of a neutron powder diffraction pattern based on the model used in a successful analysis of the superconductor 2H-NaxCoO2 center dot yD(2)O (x similar or equal to 0.35, y similar or equal to 1.3). Intensity distributions were calculated based on a superstructure expression of a commensurate composite crystal model, where the structures of the CoO2 part (a(1) = b(1) = 2.82 angstrom) and the guest (a(2) = b(2) = 3.26 angstrom) with short-range order stacking are described on a cell of A = B = 2a(1) = 3(1/2) a(2) = 5.64 angstrom, and with alternate stacking based on c = 4.9 angstrom. It is shown that the most conspicuous diffuse reflection band corresponds to the main reflection scattering of the guest sheet, with local maxima at half-integer positions of zeta' based on the stacking distance 2c, and that the Bragg diffraction components of the host and gues! t are coherent in terms of the peak height at integer zeta '' based on 4c.
Title:
Influence of quasicrystalline phase on transport processes in Zr70Pd30 amorphous alloy
Authors:
Pekala, K; Antonowicz, J; Jaskiewicz, P; Drobiazg, T; Konupek, J Author Full Names: Pekala, Krystyna; Antonowicz, Jerzy; Jaskiewicz, Piotr; Drobiazg, Tomasz; Konupek, Jan
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 500 (2): 145-148 JUN 25 2010
Abstract:
Electron transport and structural properties of amorphous Zr75Pd30 alloy are investigated by electrical resistivity, thermoelectric power, differential scanning calorimetry and X-ray diffraction methods. It was found that appearance of the icosahedral quasicrystalline phase in the first crystallization stage contributes to an increase of the electrical resistivity and Seebeck coefficient. Temperature variation of transport properties in amorphous phase excludes a variable range hopping model, which supplies unreasonable values of hopping energy and hopping distance. A similar degree of agreement between experimental results and both the Ziman and weak localization models is found for the electrical resistivity. However, a relatively high content of early transition Zr atoms in the alloy points rather that the weak localization may play a role. (C) 2010 Elsevier B.V. All rights reserved.
Title:
o '-Al13Co4, a new quasicrystal approximant
Authors:
Fleischer, F; Weber, T; Jung, DY; Steurer, W Author Full Names: Fleischer, F.; Weber, T.; Jung, D. Y.; Steurer, W.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 500 (2): 153-160 JUN 25 2010
Abstract:
The crystal structure of o '-Al13Co4, a new Al13TM4 (TM = transition metal) modification was determined by single-crystal X-ray diffraction. The phase, with Pearson symbol oP204-x (x=6), crystallizes in the orthorhombic space group Pnma (No. 62) with lattice parameters a = 28.890(4) angstrom, b = 8.138(2) angstrom and c = 12.346(1) angstrom. The structure, which can be seen as a stacking of four flat and puckered atomic layers along the pseudo-tenfold b axis, is closely related to o-Al13Co4 and m-Al13Co4. First-principles total-energy calculations indicate that all these related Al13Co4 modifications, some of them stabilized by vacancies, seem to be slightly unstable at low temperatures. (C) 2010 Elsevier B.V. All rights reserved.
Title:
The magnetoelectric effects in weak ferromagnetic YMn2O5 modulated structure: a Landau theory approach
Authors:
Tehranchi, MM; Phirouznia, A Author Full Names: Tehranchi, M. M.; Phirouznia, A.
Source:
EUROPEAN PHYSICAL JOURNAL B 75 (4): 439-442 JUN 2010
Abstract:
According to the group theory approach, linear magnetoelectric effect (ME) can not be obtained for the spatial group of YMn2O5, which was known to be mmm. Regard to the magnetic structure of these type of materials, we propose a magnetic group structure for the YMn2O5 by considering spin orientation of the Mn3+ and Mn4+ ions. According to the landau theory of phase transition it can be shown, how symmetrical rules result in relationship between quantities such as magnetic order, polarization, and etc. This relation shows a weak ferromagnetic state, associated with spontaneous polarization, arisen by Dzyaloshinskii-Moriya type interaction and a field induced change in magnetoelectrical susceptibility.

Update: 9-Jul-2010

Title:
THE Al-Cu-Ir ISOTHERMAL SECTION AT 800 degrees C IN THE ALUMINUM-RICH RANGE
Authors:
Kapush, DO; Grushko, B; Velikanova, TY Author Full Names: Kapush, D. O.; Grushko, B.; Velikanova, T. Ya.
Source:
POWDER METALLURGY AND METAL CERAMICS 49 (1-2): 79-85 MAY 2010
Abstract:
The partial isothermal section at 800 degrees C is represented for the first time. The structure of the Al-Cu-Ir alloys in the Al70Ir30-Al40Cu60-Al range, which are quenched from 800 degrees C, is investigated by SEM/EDX and XRD methods. Three ternary phases (decagonal quasicrystalline D-1, orthorhombic epsilon(6), and cubic (fcc) C-2) are stable at this temperature. The (Al9Ir2), phi, epsilon(6), D-1, gamma(1), and epsilon(2) phases coexist with a liquid phase at 800 degrees C.
Title:
Surface Charge Density Wave Phase Transition in NbSe3
Authors:
Brun, C; Wang, ZZ; Monceau, P; Brazovskii, S Author Full Names: Brun, Christophe; Wang, Zhao-Zhong; Monceau, Pierre; Brazovskii, Serguei
Source:
PHYSICAL REVIEW LETTERS 104 (25): Art. No. 256403 JUN 24 2010
Abstract:
The two charge-density wave (CDW) transitions in NbSe3 were investigated by scanning tunneling microscopy (STM) on an in situ cleaved (b, c) plane. The temperature dependence of first-order CDW satellite spots, obtained from the Fourier transform of the STM images, was measured between 5 and 140 K to extract the surface critical temperatures (T-s). The low-T CDW transition occurs at T-2s = 70-75 K, more than 15 K above the bulk T-2b = 59 K while at exactly the same wave number. A plausible mechanism for such an unusually high surface enhancement is a softening of transverse phonon modes involved in the CDW formation. The regime of 2D fluctuations is analyzed according to a Berezinskii-Kosterlitz-Thouless type of surface transition, expected for this incommensurate 2D CDW, by extracting the temperature dependence of the order parameter correlation functions.
Title:
Domains and Domain Walls in Multiferroic Ferroelectric-Ferromagnet and Control of Its Modulation
Authors:
Lykah, VA Author Full Names: Lykah, V. A.
Source:
FERROELECTRICS 398: 71-76 2010
Abstract:
Ferroelectric-ferromagnet with inhomogeneous exchange-relativistic magneto-electric interaction (Dzyaloshinskii-Moriya) is studied theoretically in external electric field. The domain wall combines properties of usual 180 degrees. one in ferroelectric and unusual magnetic one, consisting of linear topological defects (Bloch lines), situated periodically with large density. It is shown that the external electric field changes both ferroelectric and ferromagnetic subsystems. It is found that the helicoids step is formed in each domain in the magnetic subsystem and Bloch lines period demonstrates incommensurate structure. Final solution for magnetic moment in Bloch lines and modulated helicoids period near domain wall can be expressed in Jacobian elliptic functions.
Title:
Tricritical Behavior of Sn2P2S6 Ferroelectrics at Hydrostatic Pressure
Authors:
Vysochanskii, YM; Kohutych, AA; Kityk, AV; Zadorozhna, AV; Khoma, MM; Grabar, AA Author Full Names: Vysochanskii, Yu. M.; Kohutych, A. A.; Kityk, A. V.; Zadorozhna, A. V.; Khoma, M. M.; Grabar, A. A.
Source:
FERROELECTRICS 399: 83-88 2010
Abstract:
For Sn2P2S6 ferroelectrics with three-well potential under hydrostatic compression the second order phase transition approaches tricritical point as expected according to Blume-Emery-Griffiths (BEG) model. Joint consideration of BEG model and known ANNNI model, describing the incommensurate phase appearing as a result of competitive interactions, allows one to draw conclusion about possibility of tricritical point presence on temperature-pressure diagram of Sn2P2S6 without incommensurate phase appearing. Investigations of temperature dependences of longitudinal ultrasound velocity at different pressures for Sn2P2S6 crystals confirm such conclusion.
Title:
Synthesis, Spectroscopic and Magnetic Properties of the Co-2(OH)(PO4)(1-x)-(AsO4)(x) [0 <= x <= 1] Solid Solution
Authors:
de Pedro, I; Rojo, JM; Fernandez, JR; Lezama, L; Rojo, T Author Full Names: de Pedro, Imanol; Maria Rojo, Jose; Rodriguez Fernandez, Jesus; Lezama, Luis; Rojo, Teofilo
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY (17): 2514-2522 JUN 2010
Abstract:
The Co-2(OH)(PO4)(1-x)(AsO4)(x) [0 <= x <= 1] solid solution was prepared by hydrothermal synthesis and, polycrystalline samples characterized by X-ray powder diffraction and spectroscopic measurements. The cell parameters of the isostructural phosphate-arsenate phases follow Vegard's law in the whole range of composition. The IR spectra are characteristic of three distinct features corresponding principally to the vibrations of both the hydroxide and tetrahedral (XO4)(3-) (X = P, As) groups together with the evolution of the intensity of stretching [vas (X-O)] vibration modes corresponding to the PO4 and AsO4 tetrahedra in the solid solution. Diffuse reflectance data show bands belonging to the octahedral and trigonal bipyramidal geometries of the Co2+ ions with a high degree of covalence in the Co-O bonds of the arsenate phases. Magnetization measurements of Co-2(OH)(PO4)(1-x)(AsO4)(x) [0 <= x <= 1] show the existence of antiferromagnetic interactions with the presence of a ferromagnetic component below the ordering temperature. TN decreases from 71 to 19 K as the arsenate amount is increased. ZFC-FC curves show irreversibility just below T-N for Co-2(OH)(PO4)(1-x)(AsO4)(x) [x = 0.1-0.75]. The magnetic behavior of Co-2(OH)(PO4)(0.1)(AsO4)(0.9) is completely different from the rest of the hydroxyphosphate-arsenate members and similar to that observed in the undoped arsenate compound where an incommensurate magnetic phase is observed.
Title:
Incommensurate spin density wave in Co-doped BaFe2As2
Authors:
Bonville, P; Rullier-Albenque, F; Colson, D; Forget, A Author Full Names: Bonville, P.; Rullier-Albenque, F.; Colson, D.; Forget, A.
Source:
EPL 89 (6): Art. No. 67008 MAR 2010
Abstract:
Fe-57 Mossbauer spectroscopy measurements are presented in the underdoped Ba(Fe1-xCox)(2)As-2 series for x=0.014 (T-c < 1.4K) and x=0.03 and 0.045 (T-c similar or equal to 2 and 12K, respectively). The spectral shapes in the so-called spin density wave (SDW) phase are interpreted in terms of incommensurate modulation of the magnetic structure, and allow the shape of the modulation to be determined. In undoped BaFe(2)A(s)2, the magnetic structure is commensurate, and we. nd that incommensurability is present at the lowest doping level (x= 0.014). As Co doping increases, the low-temperature modulation progressively loses its " squaredness" and tends to a sine-wave. The same trend occurs for a given doping level, as temperature increases. We. nd that a magnetic hyper. ne component persists far above the SDW transition, its intensity being progressively tranferred to a paramagnetic component on heating. Copyright (C) EPLA, 2010 Resistivity
Title:
Mossbauer spectroscopy of spin dynamics in MnxFe1-xSe0.85 superconductors: Evidence for an incommensurate-spin-density-wave state
Authors:
Hamdeh, HH; El-Tabey, MM; Asmatulu, R; Ho, JC; Huang, TW; Yeh, KW; Wu, MK Author Full Names: Hamdeh, H. H.; El-Tabey, M. M.; Asmatulu, R.; Ho, J. C.; Huang, T. W.; Yeh, K. W.; Wu, M. K.
Source:
EPL 89 (6): Art. No. 67009 MAR 2010
Abstract:
In the tetragonal crystalline structure of MnxFe(1-x)Se(0.85), the magnetic state contains low-and high-spin Fe2+, with high-spin numbers equal to that of the combined Mn substitute and Se deficiency atoms. The state is pinned by " spin-hopping" around substitution centers via highspin. low-spin conversions. During the structural distortion from tetragonal to orthorhombic, from 90K to 70K, the rate of spin conversions increases and the iterant character of the magnetic state is enhanced. In the orthorhombic structure, the spin dynamics evolve into an incommensurate spin-density wave (ISDW). Excitations of the ISDW decrease with temperature and level out across the superconducting phase. The ISDW appears to have more than one oscillation mode and contributions from high-order harmonics. Copyright (C) EPLA, 2010
Title:
Large increase in perpendicular giant magnetoresistance of quasiperiodic magnetic multilayers
Authors:
Tao, YC Author Full Names: Tao, Y. C.
Source:
EPL 90 (2): Art. No. 27005 APR 2010
Abstract:
Combining the transfer matrix method with Landauer-Buticker formalism, we study the spin-polarized transport in the current-perpendicular-to-the plane (CPP) geometry of a quasiperiodic magnetic multilayered structure consisting of a ferromagnet (FM) and a nonmagnet (NM) arranged in a Fibonacci sequence. The CPP giant magnetoresistance (GMR) in the quasiperiodic structure is found to be largely enhanced compared with that in the periodic one. It is also shown that there are the same and different properties in the variations of the relative conductivities and of the GMR with the number of bilayers between the quasiperiodic and periodic structures, implying that there exist common and different physical origins in them. Copyright (C) EPLA, 2010

Update: 2-Jul-2010

Title:
Synthesis and brittle-to-ductile transition of the omega-Al0.7Cu0.2Fe0.1 tetragonal phase
Authors:
Laplanche, G; Joulain, A; Bonneville, J; Gauthier-Brunet, V; Dubois, S Author Full Names: Laplanche, G.; Joulain, A.; Bonneville, J.; Gauthier-Brunet, V.; Dubois, S.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 527 (16-17): 4515-4518 JUN 25 2010
Abstract:
Synthesis of omega-Al-Cu-Fe single phase material is reported. Microhardness tests performed over the temperature range 293-898 K indicate a brittle-to-ductile transition between 673 K and 823 K. Fracture toughness was determined from indentation cracks at 293 K. Both the hardness and fracture toughness are comparable to that of the icosahedral Al0.635Cu0.240Fe0.125 material. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Structural themes in approximant and decagonal quasicrystalline phases in Al based alloys
Authors:
Boudard, M Author Full Names: Boudard, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 495 (2): 365-371 APR 16 2010
Abstract:
The structure of two periodic phases in the Al-Pd-Mn system showing the importance of chemical ordering in the formation of decagonal quasicrystalline and approximant crystalline structures is reviewed Different descriptions of the periodic phases in terms of clusters, dense planes and pentagonal chains of transition metals are presented. We also review a structural model for AlPdMn decagonal quasicrystals derived from the general schematic distribution of TM existing in the approximant phases This model is discussed in relation of an unique decagonal overlapping cluster in a Penrose pentagonal tiling. (C) 2009 Elsevier B V All rights reserved.
Title:
Nanoquasicrystalline Al-Fe-Cr-based alloys with high strength at elevated temperature
Authors:
Galano, M; Audebert, F; Escorial, AG; Stone, IC; Cantor, B Author Full Names: Galano, Marina; Audebert, Fernando; Garcia Escorial, Asuncion; Stone, Ian C.; Cantor, Brian
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 495 (2): 372-376 APR 16 2010
Abstract:
Nanoquasicrystalline Al-Fe-Cr-based alloys have a microstructure composed of nanoquasicrystalline particles embedded in an alpha-Al matrix, and have high strength at elevated temperatures. However, the metastability of the quasicrystalline phase can limit the use of these alloys at elevated temperatures The microstructure, stability and mechanical properties at different temperatures on melt-spun nanoquasicrystalline Al-Fe-Cr-based alloys containing Ti, V, Nb or Ta have been studied and summarized in the present work The structural characterisation was carried out by means of X-ray diffraction, hot-stage transmission electron microscopy and scanning-transmission electron microscopy The addition of a fourth element to the Al-93(Fe3Cr2)(7) alloy increases the thermal stability, in particular in the case of the Nb and Ta containing alloys, leading to the delay of the phase transformation towards the melting of the alloys. The mechanical properties at elevated temperatures were studied by tensile tests at different test temperatures with different pre-heat treatments. All the alloys showed a very high strength up to 350 C, more than five times the strength of the commercial Al alloys. These values and the enhanced thermal stability achieved in the quaternary nanoquasicrystalline Al-Fe-Cr-(Ti, V, Nb or Ta) alloys make these alloys very promising for industrial applications. (C) 2009 Elsevier B.V All rights reserved
Title:
Laser remelting of Al91Fe4Cr3Ti2 quasicrystalline phase former alloy
Authors:
Gargarella, P; Vilar, R; Almeida, A; Kiminami, CS; Rios, CT; Bolfarini, C; Botta, WJ Author Full Names: Gargarella, P.; Vilar, R.; Almeida, A.; Kiminami, C. S.; Rios, C. T.; Bolfarini, C.; Botta, W. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 495 (2): 646-649 APR 16 2010
Abstract:
In the present work, an Al-Fe-Cr-Ti alloy with adequate composition to form quasicrystalline phases has been surface remelted using laser processing techniques The surface of spray formed Al91Fe4Cr3Ti2 bulk samples was remelted using a 2 kW CW Nd:YAG laser. Two different laser beam powers were applied with the goal of studying its influence in the quasicrystalline phase formation in the remelted coating. After laser treatment, the samples were characterized by X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (FEG-SEM). The formation of quasicrystalline phases was observed in the X-ray diffractograms and their transformations were verified in DSC analyses. A greater formation of quasicrystalline phase was verified in the coating produced with smaller laser beam power, i.e. higher cooling rate, and its morphology was more close to the sphere. The results indicate the possibility of producing low density coatings conta! ining quasicrystalline phases by laser remelting of spray formed materials Crown Copyright (C) 2009 Published by Elsevier B V All rights reserved.
Title:
Interdependence between glass stability and phase formation sequence during crystallization of Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass
Authors:
Mechler, N; Wanderka, N; Macht, MP Author Full Names: Mechler, S.; Wanderka, N.; Macht, M. -P.
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH 101 (5): 601-610 MAY 2010
Abstract:
Knowledge of the crystallization sequence of metallic glasses can yield a deep insight into the origin of their thermal stability. Crystallization of metallic glasses often leads to the simultaneous formation of different metastable crystalline phases that makes their identification difficult. In order to separate formation of crystalline phases from each other, long term isothermal pre-annealing below the glass transition temperature of Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk metallic glass prior to crystallization was performed. It is found that this pre-annealing strongly influences the crystallization sequence and depending on the pre-annealing time leads to preferential formation of different phases. In addition to the well known intermetallic Be2Zr phase and a quasicrystalline phase, three further previously unknown crystalline phases are identified and described in terms of their structure and composition. The formation of the crystalline phases is discussed with respect to the glass forming ability and thermal stability of the glass phase.
Title:
Strong crystalline field at the Fe site and spin rotation in olivine LiNi0.99 Fe-57(0.01) PO4 material by Mossbauer spectroscopy
Authors:
Kim, W; Rhee, CH; Kim, HJ; Moon, SJ; Kim, CS Author Full Names: Kim, Woochul; Rhee, Chan Hyuk; Kim, Hyung Joon; Moon, Seung Je; Kim, Chul Sung
Source:
APPLIED PHYSICS LETTERS 96 (24): Art. No. 242505 JUN 14 2010
Abstract:
The crystal structure of LiNi0.99 Fe-57(0.01) PO4 compound has been determined to be orthorhombic by Rietveld refinement method. Temperature dependence of magnetization M shows an anomalous antiferromagnetic behavior. A sudden change in both the magnitude of magnetic hyperfine field and its slope below 11 K suggests that magnetic phase transition related to the spin ordering takes place abruptly. From the result of Moumlssbauer measurement, it is shown that a strong electric crystalline field of octahedral symmetry including the contribution of spin-orbit coupling and magnetic hyperfine field by space-modulated spin structure is acted to the sites of Fe2+ ions simultaneously at low temperature. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3455312]
Title:
Structure factor for decorated Penrose tiling in physical space
Authors:
Kozakowski, B; Wolny, J Author Full Names: Kozakowski, Bartlomiej; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 66: 489-498 Part 4 JUL 2010
Abstract:
The structure factor for an arbitrarily decorated Penrose tiling has been calculated in the average unit cell description. The obtained formula uses only the physical coordinates of the atoms decorating a structure. The final equation can be easily extended so that it can describe the other physical properties of a structure. Its usefulness is demonstrated by its use in the Al-Ni-Co alloy structure-refinement process. (c) 2010 International Union of Crystallography Printed in Singapore - all rights reserved

Update: 25-Jun-2010

Title:
Polychromatic Photonic Quasicrystal Cavities
Authors:
Thon, SM; Irvine, WTM; Kleckner, D; Bouwmeester, D Author Full Names: Thon, Susanna M.; Irvine, William T. M.; Kleckner, Dustin; Bouwmeester, Dirk
Source:
PHYSICAL REVIEW LETTERS 104 (24): Art. No. 243901 JUN 14 2010
Abstract:
Photonic crystal slabs provide unique opportunities for the manipulation of light on semiconductor chips. The patterns of holes in the slabs are typically designed to maximize the width, depth and symmetry of a single photonic band gap. Quasicrystalline patterns are ideal from this point of view; here, we show that, owing to the presence of multiple Bragg scattering length scales, they also have the desirable property of supporting multiple photonic band gaps in the same slab. This opens up the possibility of creating polychromatic cavities that could be used to extend the possibilities for single photons on optical chips, including on-chip frequency conversion in III-V semiconductors. We study several quasicrystalline structures which support high quality cavity modes at multiple resonant frequencies using 2D and 3D FDTD simulations.
Title:
Symmetry replication and toroidic effects in the multiferroic pyroxene NaFeSi2O6
Authors:
Mettout, B; Toledano, P; Fiebig, M Author Full Names: Mettout, Bruno; Toledano, Pierre; Fiebig, Manfred
Source:
PHYSICAL REVIEW B 81 (21): Art. No. 214417 JUN 11 2010
Abstract:
The magnetoelectric and toroidic effects occurring in NaFeSi2O6 are analyzed theoretically. The symmetry-breaking mechanism giving rise to the incommensurate antiferromagnetic-ferroelectric phase observed below 6 K is shown to be induced by replication of a single transition order parameter. It implies an effective-continuous symmetry of the system identified as the phason rotation of the incommensurate order parameter. The magnetic-field induced toroidal moment is expressed in terms of the macroscopic and spin variables. It shows that the toroidal susceptibility components vary critically as the electric polarization, denoting the inherently magnetoelectric nature of the scaling properties of the ferrotoroidic state. The toroidal moment arising under applied field in antiferromagnetic-ferroelectric structures is induced simultaneously with a spin wave which exhibits the same symmetry properties but spans different degrees of freedom. The difference between microscopic spins degrees of freedom and the electromagnetic macroscopic magnetization and toroidal fields is emphasized.
Title:
Zigzag ladders with staggered magnetic chirality in the S=3/2 compound beta-CaCr2O4
Authors:
Damay, F; Martin, C; Hardy, V; Maignan, A; Andre, G; Knight, K; Giblin, SR; Chapon, LC Author Full Names: Damay, Francoise; Martin, Christine; Hardy, Vincent; Maignan, Antoine; Andre, Gilles; Knight, Kevin; Giblin, Sean R.; Chapon, Laurent C.
Source:
PHYSICAL REVIEW B 81 (21): Art. No. 214405 JUN 7 2010
Abstract:
The crystal and magnetic structures of the S=3/2 antiferromagnet beta-CaCr2O4 have been investigated by means of specific heat, magnetization, muon relaxation, and neutron powder diffraction between 300 and 1.5 K. In this compound, in which the unusual topology of the Cr3+ magnetic lattice can be described as a network of triangular "zigzag" ladders with legs parallel to c, a complex antiferromagnetic ordering with an incommensurate propagation vector k=(0,0,q) (q similar to 0.477 at 1.5 K) is evidenced below T-N=21 K. This complex magnetic ordering can be described as a honeycomblike arrangement of cycloids, running along c, and presenting a unique pattern of staggered chirality. To understand the experimental observation of this staggered chirality, we propose to use antisymmetric Dzyaloshinskii-Moriya terms in the exchange Hamiltonian.
Title:
Transport between twisted graphene layers
Authors:
Bistritzer, R; MacDonald, AH Author Full Names: Bistritzer, R.; MacDonald, A. H.
Source:
PHYSICAL REVIEW B 81 (24): Art. No. 245412 JUN 8 2010
Abstract:
Commensurate- incommensurate transitions are ubiquitous in physics and are often accompanied by intriguing phenomena. In few-layer graphene (FLG) systems, commensurability between honeycomb lattices on adjacent layers is regulated by their relative orientation angle theta, which is in turn dependent on sample preparation procedures. Because incommensurability suppresses interlayer hybridization, it is often claimed that graphene layers can be electrically isolated by a relative twist, even though they are vertically separated by a fraction of a nanometer. We present a theory of interlayer transport in FLG systems which reveals a richer picture in which the specific conductance depends sensitively on theta, single-layer Bloch-state lifetime, in-plane magnetic field, and bias voltage. We find that linear and differential conductances are generally large and negative near commensurate values of theta, and small and positive otherwise. We show that accounting for interlayer coupling may be essential for describing transport in FLG despite its physically insignificant effect on the band structure of the system.
Title:
IDENTIFICATION OF A QUASICRYSTALLINE PHASE IN THE Al-Cu-Fe SYSTEM
Authors:
Kalmykov, KB; Zvereva, NL; Dunaev, SF; Kazennov, NV Author Full Names: Kalmykov, K. B.; Zvereva, N. L.; Dunaev, S. F.; Kazennov, N. V.
Source:
METAL SCIENCE AND HEAT TREATMENT 51 (9-10): 440-443 SEP 2009
Abstract:
The methods of scanning and transmission electron microscopy, x-ray phase analysis, and energy dispersive microanalysis are used to study alloys of the Al - Cu - Fe system in the aluminum-rich domain. The range of existence of a quasicrystalline i-phase with composition Al62.5Cu25Fe12.5 is determined.
Title:
Single-molecule probing of incommensurate biphenyl
Authors:
Pars, M; Palm, V; Kikas, J Author Full Names: Paers, M.; Palm, V.; Kikas, J.
Source:
LOW TEMPERATURE PHYSICS 36 (5): 448-450 MAY 2010
Abstract:
Our data on the distribution of purely electronic linewidths of single molecules of terrylene in incommensurate biphenyl crystals are compared with the data obtained by other groups for different low-temperature organic solid hosts and with results of numerical simulations. The first two moments of the distributions measured within a narrow temperature interval have been used to calculate a single dimensionless parameter characterizing each of the respective hosts-the variation coefficient. It appears that different amorphous hosts have similar values of this coefficient, but the value obtained for the incommensurate crystal of biphenyl is significantly different. One can conclude that the remarkable single-molecule line broadening in biphenyl at 1.8 K cannot be solely explained by the interaction with two-level systems, which is considered to cause the broadening in amorphous hosts. (C) 2010 American Institute of Physics.
Title:
Observation of twin-like composition modulation and phase separation with long-range order induced by oxygen deficiency in single crystal manganites
Authors:
Jia, RR; Feng, ZJ; Wang, SP; Liu, YS; Jing, C; Cao, SX; Zhang, JC Author Full Names: Jia, Rongrong; Feng, Zhenjie; Wang, Shipeng; Liu, Yongsheng; Jing, Chao; Cao, Shixun; Zhang, Jincang
Source:
JOURNAL OF CRYSTAL GROWTH 312 (12-13): 1963-1967 JUN 1 2010
Abstract:
Single crystal La2/3Sr1/3MnO3-delta manganite with an unusual structure was obtained by the optical-floating method with controlled growth in a flowing argon atmosphere. A modulated twin-like structure with phase separation characteristics in the long-range order is found. The energy-dispersive X-ray spectroscopy measurement reveals that there is a strong chemical fluctuation for different stripes, i.e. resulting from the nonstoichiometry due to oxygen deficiency. After annealing, the twin-like stripe phase disappears and the single crystal shows excellent properties. These results may be of great significance for controlled growth of oxide electronics materials with artificial superstructure-like technique. (C) 2010 Elsevier B.V. All rights reserved.

Update: 18-Jun-2010

Title:
Effects of Nd and high-valence Mn co-doping on the electrical and magnetic properties of multiferroic BiFeO3 ceramics
Authors:
Hu, ZQ; Li, MY; Yu, Y; Liu, J; Pei, L; Wang, J; Liu, XL; Yu, BF; Zhao, XZ Author Full Names: Hu, Zhongqiang; Li, Meiya; Yu, Yang; Liu, Jun; Pei, Ling; Wang, Jing; Liu, Xiaolian; Yu, Benfang; Zhao, Xingzhong
Source:
SOLID STATE COMMUNICATIONS 150 (23-24): 1088-1091 JUN 2010
Abstract:
Pure BiFeO3 (BFO), 15% Nd doped BFO (BNF), and 15% Nd and 2% high-valence Mn co-doped BFO (BNFM) multiferroic ceramics were prepared by a rapid liquid phase sintering technique. A structural transition from rhombohedral R3c to orthorhombic P4mm occurred in the BNF and BNFM ceramics. The co-doped BNFM ceramics exhibit the largest dielectric constant, the smallest dielectric loss and leakage current, and an improved rectangular-shaped polarization hysteresis loop with a remnant polarization as high as 31 mu C/cm(2), which could be attributed to the lower concentration of charge defects and the structural transition. Besides, enhanced ferromagnetism is confirmed in BNFM with a remnant magnetization of 0.075 emu/g and a coercive magnetic field of 5.8 kOe, which might be attributed to the effective suppression of the spatially modulated spin structure by the Nd and Mn co-doping. (C) 2010 Elsevier Ltd. All rights reserved.
Title:
Hydrogen in the approximant i-TiZrHf: The energy state, charge, and diffusion
Authors:
Belov, MP; Isaev, EI; Vekilov, YK Author Full Names: Belov, M. P.; Isaev, E. I.; Vekilov, Yu. Kh.
Source:
PHYSICS OF THE SOLID STATE 52 (6): 1111-1114 JUN 2010
Abstract:
The energy of hydrogen dissolution in different tetrahedral pores of a 1/1 approximant of the icosahedral TiZrHf quasicrystal has been determined in terms of the density functional theory and ab initio pseudopotentials. At low and high degrees of loading of TiZrHf with hydrogen, the charges of atoms involved in the system and the Mayer bond order have been calculated for all possible M-M and M-H pairs. The diffusion coefficient of a single hydrogen atom in the system under study has been estimated numerically.
Title:
Frustration of the stable Zr-Ti-Ni quasicrystal as the basis of glass formation
Authors:
Mechler, S; Macht, MP; Schumacher, G; Zizak, I; Wanderka, N Author Full Names: Mechler, S.; Macht, M. -P.; Schumacher, G.; Zizak, I.; Wanderka, N.
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 180101 MAY 1 2010
Abstract:
The origin of glass formation and the systematics of quasicrystal formation in Zr-Ti-Ni-(Cu-Be)-based metallic glasses is unraveled. Both are found to rely on frustration of the stable Zr41.5Ti41.5Ni17 quasicrystal. A systematic change in composition of the stable Zr-Ti-Ni quasicrystal prevents icosahedral order from direct growth in the deeply undercooled liquid and induces the glass transition. Quasicrystals form in the amorphous phase to reduce frustration, i.e., to recover the ideal symmetry and composition of the stable Zr-Ti-Ni quasicrystal. This relation is established especially by the discovery of a new type of sequential phase transformations of icosahedral quasicrystalline phases involving chemical redistribution.
Title:
Anisotropic physical properties of the Al13Fe4 complex intermetallic and its ternary derivative Al-13(Fe, Ni)(4)
Authors:
Popcevic, P; Smontara, A; Ivkov, J; Wencka, M; Komelj, M; Jeglic, P; Vrtnik, S; Bobnar, M; Jaglicic, Z; Bauer, B; Gille, P; Borrmann, H; Burkhardt, U; Grin, Y; Dolinsek, J Author Full Names: Popcevic, P.; Smontara, A.; Ivkov, J.; Wencka, M.; Komelj, M.; Jeglic, P.; Vrtnik, S.; Bobnar, M.; Jaglicic, Z.; Bauer, B.; Gille, P.; Borrmann, H.; Burkhardt, U.; Grin, Yu; Dolinsek, J.
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 184203 MAY 1 2010
Abstract:
We have investigated the magnetic susceptibility, the electrical resistivity, the specific heat, the thermoelectric power, the Hall coefficient, and the thermal conductivity of the Al13Fe4 and Al13(Fe, Ni)(4) monoclinic approximants to the decagonal quasicrystal. While the Al13Fe4 crystals are structurally well ordered, the ternary derivative Al-13(Fe, Ni)(4) contains substitutional disorder and is considered as a disordered version of the Al13Fe4. The crystallographic-direction-dependent measurements were performed along the a*, b, and c directions of the monoclinic unit cell, where the (a*, c) atomic planes are stacked along the b direction. The electronic transport and the magnetic properties exhibit significant anisotropy. The stacking b direction is the most conducting direction for the electricity and heat. The effect of substitutional disorder in Al-13(Fe, Ni)(4) is manifested in the large residual resistivity rho(T -> O) and significantly reduced thermal conductivity of this compound, as compared to the ordered Al13Fe4. Specific-heat measurements reveal that the electronic density of states at the Fermi level of both compounds is high. The anisotropic Hall coefficient R-H reflects complex structure of the anisotropic Fermi surface that contains electronlike and holelike contributions. Depending on the combination of directions of the current and the magnetic field, electronlike (R-H<0) or holelike (R-H>0) contributions may dominate, or the two contributions compensate each other (R-H approximate to 0). Similar complicated anisotropic behavior was observed also in the thermopower. The anisotropic Fermi surface was calculated ab initio using the atomic parameters of the refined Al13Fe4 structural model that is also presented in this work.
Title:
Anisotropic physical properties of the Taylor-phase T-Al72.5Mn21.5Fe6.0 complex intermetallic
Authors:
Heggen, M; Feuerbacher, M; Ivkov, J; Popcevic, P; Batistic, I; Smontara, A; Jagodic, M; Jaglicic, Z; Janovec, J; Wencka, M; Dolinsek, J Author Full Names: Heggen, M.; Feuerbacher, M.; Ivkov, J.; Popcevic, P.; Batistic, I.; Smontara, A.; Jagodic, M.; Jaglicic, Z.; Janovec, J.; Wencka, M.; Dolinsek, J.
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 184204 MAY 1 2010
Abstract:
We have investigated anisotropic physical properties (the magnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient and the thermal conductivity) of the single-crystalline Taylor-phase T-Al72.5Mn21.5Fe6.0 complex intermetallic that is an orthorhombic approximant to the d-Al-Mn-Pd decagonal quasicrystal. The measurements were performed along the a, b, and c directions of the orthorhombic unit cell, where (a, c) atomic planes are stacked along the perpendicular b direction. The T-Al72.5Mn21.5Fe6.0 shows spin-glass behavior below the spin-freezing temperature T-f approximate to 29 K with a small anisotropy in the magnetic susceptibility. The anisotropic electrical resistivities are rather large and show negative temperature coefficient. The resistivity is lowest along the stacking direction, which appears to be a common property of the decagonal-approximant phases with a stacked-layer structure. The temperature-dependent resis! tivity was theoretically reproduced by the quantum transport theory of slow charge carriers. The thermopower is positive for all three crystallographic directions, indicating that holes are the majority charge carriers, and no anisotropy can be claimed within the experimental precision. The same conclusion on the holes being the dominant charge carriers follows from the Hall-coefficient measurements, which is a sum of the (positive) normal Hall coefficient and the anomalous term, originating from the magnetization. The anisotropy of the thermal conductivity is practically negligible. The T-Al72.5Mn21.5Fe6.0 Taylor phase can be considered as a "close-to-isotropic" complex intermetallic. The relation of the anisotropic physical properties of the Taylor phase to other families of decagonal-approximant phases with the stacked-layer structure is discussed.
Title:
Incommensurate spin-density wave and magnetic lock-in transition in CaFe4As3
Authors:
Manuel, P; Chapon, LC; Todorov, IS; Chung, DY; Castellan, JP; Rosenkranz, S; Osborn, R; Toledano, P; Kanatzidis, MG Author Full Names: Manuel, P.; Chapon, L. C.; Todorov, I. S.; Chung, D. Y.; Castellan, J. -P.; Rosenkranz, S.; Osborn, R.; Toledano, P.; Kanatzidis, M. G.
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 184402 MAY 1 2010
Abstract:
The magnetic structure for the recently synthesized iron-arsenide compound CaFe4As3 has been studied by neutron-powder diffraction. Long-range magnetic order is detected below 85 K, with an incommensurate modulation described by the propagation vector k=(0, delta, 0), delta similar to 0.39. Below similar to 25 K, our measurements detect a first-order phase transition where delta locks into the commensurate value 3/8. A model of the magnetic structure is proposed for both temperature regimes, based on Rietveld refinements of the powder data and symmetry considerations. The structures correspond to longitudinal spin-density waves with magnetic moments directed along the b axis. A Landau analysis captures the change in thermodynamic quantities observed at the two magnetic transitions, in particular, the drop in resistivity at the lock-in transition.
Title:
H-T phase diagram of the two-dimensional Ising model with exchange and dipolar interactions
Authors:
Diaz-Mendez, R; Mulet, R Author Full Names: Diaz-Mendez, Rogelio; Mulet, Roberto
Source:
PHYSICAL REVIEW B 81 (18): Art. No. 184420 MAY 1 2010
Abstract:
We explore the equilibrium properties of a two-dimensional Ising spin model with short-range exchange and long-range dipolar interactions as a function of the applied magnetic field H. The model is studied through extensive Monte Carlo simulations that show the existence of many modulated phases with long-range orientational order for a wide range of fields. These phases are characterized by different wave vectors that change discontinuously with the magnetic field. In particular, the emergence of novel anharmonic phases that keep the orientational order but are characterized by several wave vectors is studied in detail. We provide numerical evidence supporting the existence of first-order transitions between modulated phases. At higher fields our results suggest a Kosterliz-Thouless scenario for the transition from a bubble to a ferromagnetic phase.
Title:
Synthesis of natural superlattice structure in the binary ZnO-Fe2O3 system by microwave irradiation
Authors:
Katayose, S; Miyazaki, T; Hayashi, Y; Takizawa, H Author Full Names: Katayose, Satomi; Miyazaki, Takamichi; Hayashi, Yamato; Takizawa, Hirotsugu
Source:
JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 118 (1377): 387-389 MAY 2010
Abstract:
Homologous compounds, Fe2O3(ZnO)(m), with the modulated natural superlattice structure were obtained within a short period by solid state reaction of component oxides under 2.45 GHz microwave irradiation. TEM observation revealed that two types of superlattice structures were observed in different Fe concentration; one is longitudinal superlattice structure in a rod shaped precipitation at high Fe concentration, and the other is modulated structure showing zigzag shape at low Fe concentration. It is conclude that the non-equilibrium nature of microwave selective heating, as well as rapid heating and quenching effects, plays a key role to form the superstructure. The obtained products exhibit ferromagnetic behavior with the Curie temperature above 300 K. (C) 2010 The Ceramic Society of Japan. All rights reserved.
Title:
Deformation-induced structural transformation leading to compressive plasticity in Zr65Al7.5Ni10Cu12.5M5 (M = Nb, Pd) glassy alloys
Authors:
Setyawan, AD; Saida, J; Kato, H; Matsushita, M; Inoue, A Author Full Names: Setyawan, Albertus D.; Saida, Junji; Kato, Hidemi; Matsushita, Mitsuhide; Inoue, Akihisa
Source:
JOURNAL OF MATERIALS RESEARCH 25 (6): 1149-1158 JUN 2010
Abstract:
Zr65Al7.5Ni10Cu12.5Nb5 glass was found to exhibit a large plastic compressive strain of over 10% and the property was suggested to be due to deformation-induced nanocrystallization. A transmission electron microscopic observation, however, only revealed obscure ordered clusters with a size of similar to 2 nm in the fracture surface of a deformed sample, instead of well-identified crystals as previously reported for the Zr-Al-Ni-Cu-Pd system. This phenomenon is suggested to correlate with the higher viscosity of supercooled liquid and the slower grain growth of icosahedral phase during primary crystallization in the Zr65Al7.5Ni10Cu12.5Nb5 compared to those in the Zr65Al7.5Ni10Cu12.5Pd5 alloy. The role of the deformation-induced nanoclusters on the enhanced compressive plasticity was discussed.
Title:
Structural and magnetic properties of magnetron sputtered Ni-Mn-Sn ferromagnetic shape memory alloy thin films
Authors:
Vishnoi, R; Kaur, D Author Full Names: Vishnoi, Ritu; Kaur, Davinder
Source:
JOURNAL OF APPLIED PHYSICS 107 (10): Art. No. 103907 MAY 15 2010
Abstract:
In the present study, structural and magnetic properties of Mn-rich, off-stoichiometric, nanocrystalline Ni-Mn-Sn ferromagnetic shape memory alloy thin films, grown on Si (100) substrates at 550 degrees C by dc magnetron sputtering have been systematically investigated. The crystallization, surface morphology, and structural features were studied using x-ray diffraction, atomic force microscopy, and field emission scanning electron microscopy. The structural transition from austenite to martensite was observed with an increase of Mn content. Austenitic phase with mixed L2(1)/A2+B2 structure has been observed at room temperature in Ni52.6Mn23.7Sn23.6 (S-1) and Ni51.5Mn26.1Sn22.2 (S-2) films, while those with composition of Ni58.9Mn28.0Sn13.0 (S-3) and Ni58.3Mn29.0Sn12.6 (S-4) show martensitic phase with 14M modulated monoclinic structures. Field induced martensite-austenite transformation has been observed in magnetization studies using superconducting quantum interference device magnetometer. Temperature dependent magnetization measurements demonstrate the influence of magnetic field on the structural phase transition temperature. The investigations reveal an increase of martensitic transformation temperature (T-M) with corresponding increase in substitution of Mn. The films exhibit ferromagnetic behavior at low temperatures below Curie temperature (T-C). The decrease in saturation moment with increasing Mn content, indicates the existence of antiferromagnetic correlations within ferromagnetic matrix. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3393961]

Update: 3-Jun-2010

Title:
Muon spin relaxation study of the layered magnetoelectric FeTe2O5Br with spin amplitude modulated magnetic structure
Authors:
Zorko, A; Pregelj, M; Berger, H; Arcon, D Author Full Names: Zorko, A.; Pregelj, M.; Berger, H.; Arcon, D.
Source:
JOURNAL OF APPLIED PHYSICS 107 (9): Art. No. 09D906 MAY 1 2010
Abstract:
Local-probe weak-transverse-field and zero-field mu SR measurements have been employed to investigate magnetic ordering in the new magnetoelectric compound FeTe2O5Br. Below the Neel transition temperature T-N=10.6 K a static local magnetic field starts to develop at the mu(+) sites. Fast mu(+) polarization decay below T-N speaks in favor of a broad distribution of internal magnetic fields, in agreement with the incommensurate magnetic structure suggested by neutron diffraction experiments. Above T-N the presence of short-range order is detected as high as at 2T(N), which suggests only weak interlayer magnetic coupling. On the other hand, strong Fe3+ spin fluctuations likely reflect geometrically frustrated structure of [Fe4O16](20-) spin clusters, which are the main building blocks of the layered FeTe2O5Br structure. (C) 2010 American Institute of Physics. [doi:10.1063/1.3362909]
Title:
Hall Coefficient of the Y-Al-Ni-Co Decagonal Approximant
Authors:
Stanic, D; Ivkov, J; Dolinsek, J; Gille, P Author Full Names: Stanic, Denis; Ivkov, Jovica; Dolinsek, Janez; Gille, Peter
Source:
CROATICA CHEMICA ACTA 83 (1): 7-10 Sp. Iss. SI APR 2010
Abstract:
We have investigated anisotropic Hall coefficient of Y-Al-Ni-Co decagonal approximant of the Al76Co22Ni2 composition. The crystalline-direction-dependent studies were performed along three orthogonal directions a*, b and c of the Y-Al-Ni-Co unit cell, where (a,c) monoclinic atomic planes are stacked along the perpendicular b direction. Hall coefficient R-H exhibits pronounced anisotropy, while at the same time the magnetic field in a given crystalline direction yields the same R-H for the current along the other two crystalline directions in the perpendicular plane. The observed anisotropy is studied in terms of the anisotropic structure of the Y-Al-Ni-Co phase and Fermi surface. The results are compared to the anisotropy of the Hall coefficient of the d-Al-Ni-Co decagonal quasicrystal reported in literature.
Title:
Anisotropic Transport Properties of the Orthorhombic Al13Co4 Approximant to the Decagonal Quasicrystal
Authors:
Lukatela, J; Stanic, D; Popcevic, P; Ivkov, J; Dolinsek, J; Gille, P Author Full Names: Lukatela, Jagoda; Stanic, Denis; Popcevic, Petar; Ivkov, Jovica; Dolinsek, Janez; Gille, Peter
Source:
CROATICA CHEMICA ACTA 83 (1): 27-32 Sp. Iss. SI APR 2010
Abstract:
Anisotropic transport properties (electrical resistivity, thermoelectric power, Hall coefficient and thermal conductivity) of the o-Al13Co4 orthorhombic approximant to the decagonal phase were investigated. The crystalline-direction-dependent measurements were performed along the a, b and c directions of the orthorhombic unit cell, where (b, c) atomic planes are stacked along the perpendicular a direction. Anisotropic electrical and thermal conductivities are the highest along the stacking a direction. The anisotropic thermoelectric power changes sign with the crystalline direction and so does the anisotropic Hall coefficient, which changes from the negative electron-like to the positive hole-like for different combinations of the electric current and magnetic field direction. The transport properties of the o-Al13Co4 phase were compared to the literature data on approximant to the decagonal quasicrystals, the Al76Co22Ni2 and the Al80Cr15Fe5, allowing for the study of evolution of transport properties with increasing structural complexity and unit cell size.
Title:
The Influence of Thermal Treatment on Magnetic Moments in i-Al-Pd-Mn Quasicrystals
Authors:
Jagodic, M; Jaglicic, Z; Grushko, B; Dolinsek, J Author Full Names: Jagodic, Marko; Jaglicic, Zvonko; Grushko, Benjamin; Dolinsek, Janez
Source:
CROATICA CHEMICA ACTA 83 (1): 39-42 Sp. Iss. SI APR 2010
Abstract:
The influence of cooling rate on thermal strains in the quasicrystalline icosahedral Al-Pd-Mn complex metallic alloy was investigated. In general, measurements of the electronic magnetization can be used as an indirect method for determining the short-scale disorder in the crystal structure as the magnetic moments at the Mn sites are highly dependent on their local environment. Excluding the contributions of thermal vacancies and second phase precipitates by proper selection of preannealing temperatures and durations, the changes in magnetization can be ascribed to the appearance or disappearance of thermal strains in the crystal structure. It was found that water-quenching increases thermal strains irrespective of previous thermal history.
Title:
The Solidification Path of the Complex Metallic Al-Mn-Be Alloy
Authors:
Markoli, B; Boncina, T; Zupanic, F Author Full Names: Markoli, Bostjan; Boncina, Tonica; Zupanic, Franc
Source:
CROATICA CHEMICA ACTA 83 (1): 49-54 Sp. Iss. SI APR 2010
Abstract:
The solidification paths of the Al86.1Mn2.5Be11.4 and Al84Mn5.1Be10.9 alloys, melt spun, cast into a copper mould and controlled cooled (during DSC) were investigated by means of light-optical microscopy (LOM), differential scanning calorimetry (DSC) combined with thermogravimetry (TG) or simultaneous thermal analysis (STA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and the X-ray diffraction (XRD) line in Elletra Trieste, Italy. The constitutions of samples from both alloys were examined in all three states, i.e., after melt spinning, after casting into a copper mould and after differential scanning calorimetry. It was established that in the cast and controlled-cooled specimens the alloys consisted of an aluminium-rich alpha(Al)-matrix, and the Al4Mn and Be4AlMn phases. In the case of casting and DSC the primary crystallization began with the precipitation of the Be4AlMn phase, followed by what can most lik! ely be characterized as a uni-variant binary eutectic reaction L -> (Be4AlMn + Al4Mn). The solidification process continued with an invariant ternary eutectic reaction, where the remaining melt (L) formed the heterogeneous structure (alpha(Al) + Al4Mn + Be4AlMn) or a ternary eutectic. When extremely high cooling rates were employed, as is the case with melt-spinning, the constituting phases of both alloys were precipitated in a very small form and the Be4AlMn phase was completely absent in the form of primary polygonal particles and replaced by the icosahedral quasicrystalline phase or the i-phase. There was also no evidence of the Al4Mn phase. The distribution, size and shape of all the constituents in the melt-spun alloys also varied from the contact surface towards the free surface of the ribbons. The smallest constituents were established at the contact surface, measuring less than 0.1 mu m, to 0.5 mu m at the free surface. The grains of the aluminium-rich matrix had mean diameters of less than 20 mu m, close to the free surface, down to 1 mu m at the contact surface.
Title:
Open Theoretical Problems in the Physics of Aperiodic Systems
Authors:
Jagannathan, A Author Full Names: Jagannathan, Anuradha
Source:
CROATICA CHEMICA ACTA 83 (1): 59-63 Sp. Iss. SI APR 2010
Abstract:
Quasicrystals have intrigued and stimulated research in a large number of disciplines. Mathematicians, physicists, chemists, metallurgists and materials scientists have found in them a fertile ground for new insights and discoveries. In the quarter century that has ensued since the publication of the experimental observation of a quasiperiodic Al-Mn alloy,(1) many different kinds of quasiperiodic alloys have been manufactured and studied. The physical properties of quasicrystals are no less interesting than the unusual structural properties that led to their discovery in 1984. In this review, some of the properties that characterize quasicrystals are presented, several types of theories that have been put forward briefly discussed, and some new behaviors that might be investigated by experiment described.
Title:
Anisotropic Transport Properties of Complex Metallic Alloys
Authors:
Smontara, A; Dolinsek, J Author Full Names: Smontara, Ana; Dolinsek, Janez
Source:
CROATICA CHEMICA ACTA 83 (1): 75-80 Sp. Iss. SI APR 2010
Abstract:
Anisotropic transport properties (electrical resistivity, rho, and thermal conductivity, kappa) of the Y-phase Al-Ni-Co, o-Al13Co4 and Al-4(Cr,Fe) complex metallic alloys were investigated. They belong to the class of decagonal approximant phases with stacked-layer crystallographic structure and allowed us to study the evolution of anisotropic transport properties with increasing structural complexity and the unit cell size.
Title:
Anisotropic Transport Properties of the Al13Fe4 Decagonal Approximant
Authors:
Popcevic, P; Smontara, A; Dolinsek, J; Gille, P Author Full Names: Popcevic, Petar; Smontara, Ana; Dolinsek, Janez; Gille, Peter
Source:
CROATICA CHEMICA ACTA 83 (1): 101-105 Sp. Iss. SI APR 2010
Abstract:
We have investigated electrical resistivity, thermoelectric power and thermal conductivity of the Al13Fe4 monoclinic approximant to the decagonal quasicrystal. The crystallographic-direction-dependent measurements were performed along the a*, b and c directions of the monoclinic unit cell, where (a*,c) atomic planes are stacked along the perpendicular b direction. The electronic transport exhibit significant anisotropy. The stacking b direction is the most conducting direction for the electricity and heat. The anisotropic thermopower reflects complicated structure of the anisotropic Fermi surface that contains electron-like and hole-like contributions.
Title:
Hall Effect of the Al13Fe4 Decagonal Approximant and Its Ternary Extension Al-13(Fe,Ni)(4)
Authors:
Ivkov, J; Popcevic, P; Dolinsek, J; Gille, P Author Full Names: Ivkov, Jovica; Popcevic, Petar; Dolinsek, Janez; Gille, Peter
Source:
CROATICA CHEMICA ACTA 83 (1): 107-111 Sp. Iss. SI APR 2010
Abstract:
We have measured Hall coefficient and electrical resistivity of the Al13Fe4 and Al-13(Fe,Ni)(4) monoclinic approximants to the decagonal quasicrystal. While the Al13Fe4 crystals are structurally well ordered, the ternary extension Al-13(Fe,Ni)(4) contains quenched disorder and can be viewed as a disordered version of Al13Fe4. The crystallographic-direction-dependent Hall effect measurements were performed along the a*, b and c directions of the monoclinic unit cell, where (a*,c) atomic planes are stacked along the perpendicular b direction. The stacking b direction is the most conducting direction for the electricity. The effect of quenched disorder in Al-13(Fe,Ni)(4) is manifested in the large residual resistivity rho(T -> 0) as compared to the ordered Al13Fe4. The Hall coefficient, R-H, values for all combinations of directions, are typical metallic. The anisotropic Hall coefficient reflects complicated structure of the anisotropic Fermi surface that contains electron-like and hole-like parts. Depending on the combination of directions of the current and magnetic field electron-like (R-H < 0) or hole-like (R-H > 0) contributions may dominate, or the two contributions compensate each other (R-H approximate to 0).
Title:
Lattice dynamics and structural phase transitions
Authors:
Shapiro, SM Author Full Names: Shapiro, S. M.
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 99 (3): 543-548 Sp. Iss. SI JUN 2010
Abstract:
Results of lattice dynamics, or atomic motions in a solid, explain many of the thermodynamic properties of solids. Inelastic neutron scattering conveniently explores the atomic motions, quantized as phonons. Of particular interest are materials that undergo structural phase transitions. The soft mode theory has been successful in relating anomalous phonon behavior to structural changes in solids. One such example is the ferromagnetic shape memory alloy, Ni2MnGa, which undergoes a sequence of phase transitions leading to a magnetic, incommensurate modulated, tetragonal phase as the ground state. The experiments, coupled with first principles calculations, provide evidence that strong electron-phonon coupling is the driving mechanism of the phase transformation.
Title:
Comparing properties of substrate-constrained and freestanding epitaxial Ni-Mn-Ga films
Authors:
Backen, A; Yeduru, SR; Kohl, M; Baunack, S; Diestel, A; Holzapfel, B; Schultz, L; Fahler, S Author Full Names: Backen, Anja; Yeduru, Srinivasa R.; Kohl, Manfred; Baunack, Stefan; Diestel, Anett; Holzapfel, Bernhard; Schultz, Ludwig; Faehler, Sebastian
Source:
ACTA MATERIALIA 58 (9): 3415-3421 MAY 2010
Abstract:
In order to use the magnetic shape memory alloy Ni-Mn-Ga with its high achievable strain of up to 10% for microactuators, freestanding epitaxial films are required. Here we show that these conditions can be fulfilled when using chromium as a sacrificial layer. The low misfit towards Ni-Mn-Ga enables epitaxial growth. Furthermore, Cr can afterwards be removed selectively by wet-chemical etching and during deposition no significant interdiffusion is observed. The structure, microstructure and magnetic properties of micrometer thick films are not affected by the etching process. Films are ferromagnetic at room temperature and we observe the coexistence of non-modulated (NM) and seven layered modulated (14 M) martensite. Tensile stress-strain measurement of a freestanding bridge reveals a broad strain plateau of 12% at a twinning stress of 25 MPa, indicating reorientation of NM variants. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 27-May-2010

Title:
Phenomenological theory of phase transitions in multiferroic MnWO4: magnetoelectricity and modulated magnetic order
Authors:
Sakhnenko, VP; Ter-Oganessian, NV Author Full Names: Sakhnenko, V. P.; Ter-Oganessian, N. V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (22): Art. No. 226002 JUN 9 2010
Abstract:
The phenomenological theory of phase transitions in multiferroic MnWO4 is suggested. The theoretical model uses the assumption that the magnetic order is driven by the instability in the (1/4; 1/2; 1/2) point of the Brillouin zone, which is justified by the symmetry of the low-temperature magnetic phase. It is shown that the experimentally observed incommensurate magnetic order is due to the Lifshitz invariants allowed for the corresponding order parameters. Invariants responsible for the magnetoelectric interaction are found and a schematic phase diagram is calculated. The influence of the magnetic field on the phase transition sequence is also analyzed. It is suggested that the description of the phase transitions in MnWO4 starting from the orthorhombic praphase significantly simplifies the approach and allows us to draw important conclusions.
Title:
TEM-assisted dynamic scanning force microscope imaging of (001) antigorite: Surfaces and steps on a modulated silicate
Authors:
Palacios-Lidon, E; Grauby, O; Henry, C; Astier, JP; Barth, C; Baronnet, A Author Full Names: Palacios-Lidon, Elisa; Grauby, Olivier; Henry, Claude; Astier, Jean-Pierre; Barth, Clemens; Baronnet, Alain
Source:
AMERICAN MINERALOGIST 95 (5-6): 673-685 MAY-JUN 2010
Abstract:
Ultra-high vacuum dynamic scanning force microscopy (dynamic SFM) has been performed on in situ cleaved and as-grown (001) surfaces of low-T, m = 18 and m = 20, antigorite from the Kovdor Mine, Russia. The internal microstructure of the same crystal before cleavage has been checked by conventional TEM on FIB-cut cross-sections. The structural wave is imaged by dynamic SFM with a similar to 0.25 nm topographic amplitude (outcropping tetrahedral sheet) on cleaved and as-grown surfaces, and with a similar to 0.5 nm topographic amplitude (outcropping tetrahedral + octahedral sheets) mostly found on cleaved surfaces. Atomic resolution imaging was successfully applied on the cleavage surface through imaging individual atomic features on the outer hexagonal net of the emerging (Mg, O, OH) octahedra of the half-wave. The antigorite cleavage crack undulates through a single octahedral sheet, thereby avoiding rupture of strong Si-O bonds. The two tetrahedral reversals, which form the edges of the modulation repeat, are found to be strongly non-equivalent in structure: across < 010 >, one reversal is sharp as expected from the standard models of the antigorite structure, whereas the other reversal is unexpectedly "extended." The latter suggests some scheme of anti-polar positioning of silicate tetrahedra along < 010 > at the 6-membered ring reversal. High-resolution transmission electron microscopy (HRTEM) structure imaging of antigorite viewed down to < 010 > confirms spread out electron densities at this reversal. Numerous step height measurements on (001) surfaces show incremental results as integral multiples of 0.25 nm, the spacing between O,OH surfaces along c. Many of them differ in height from integral multiples of the unit cell repeat along c and could be explained from carving the bulk wave structure. For all surfaces and steps, local stoichiometry and global electro-neutrality of the surface are satisfied.

Update: 13-May-2010

Title:
Low-energy lattice excitations in the decagonal Al-Ni-Fe and icosahedral Al-Cu-Fe quasicrystals and the (Al,Si)-Cu-Fe cubic phase
Authors:
Panova, GK; Zemlyanov, MG; Parshin, PP; Shikov, AA; Brand, RA Author Full Names: Panova, G. Kh.; Zemlyanov, M. G.; Parshin, P. P.; Shikov, A. A.; Brand, R. A.
Source:
PHYSICS OF THE SOLID STATE 52 (4): 771-775 APR 2010
Abstract:
The specific heat of decagonal Al71.3Ni24.0Fe4.7 and icosahedral Al62Cu25.5Fe12.5 quasicrystals and the Al55.0Si7.0Cu25.5Fe12.5 cubic phase approximating the structure of the icosahedral alloy has been studied in the temperature range 4.2-40.0 K. All the three compounds exhibit low coefficients of the electronic heat capacity and pronounced deviations of the low-temperature lattice heat capacity from a cubic temperature law in the range 5-10 K. The results obtained by the thermodynamic method and inelastic neutron scattering have been compared and analyzed. It has been established that, at energies E > < 14 meV, the spectral density of thermal vibrations in the icosahedral quasicrystal is substantially higher than those in the cubic approximant and in decagonal quasicrystal.
Title:
Investigation of the structure of compacts and sheets of an Al-Cu-Li alloy strengthened by Al2CuLi (T-1) particles
Authors:
Shamrai, VF; Timofeev, VN; Grushko, OE Author Full Names: Shamrai, V. F.; Timofeev, V. N.; Grushko, O. E.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 109 (4): 383-391 APR 2010
Abstract:
X-ray diffraction and electron microscopy have been used to investigate structural states of the material of compacts and sheets of an aluminum-copper-lithium alloy with a lithium content corresponding to the field of equilibrium of a solid solution with the phase T (1) (Al2CuLi). In pressed strips, there arises a multicomponent texture (Bs "110"aOE (c) 112 >, Cu "211"aOE (c) 111 >, S "123"aOE (c) hkl >) typical of pressed articles of aluminum-lithium alloys. Their microstructure was characterized by the presence of slip bands oriented in the rolling direction. The formation of lamellar precipitates of the T (1) phase at slip-band boundaries in the process of deformation is supposedly stimulated by Shockley partial dislocations. In hot-rolled sheets, there arose an unusually intense nearly single-component texture of the Ex (1) "011"aEuro111aEuro parts per thousand type, whose appearance is mainly caused by the cross rolling of the sheets. The reduced strength characteristics of the sheets examined are connected with a sharply oriented character of the structure of both the matrix phase and the strengthening T (1) phase. A quasicrystalline phase T (2) present in the material and the precipitates of the delta' phase exert no marked effect on the level of mechanical properties.
Title:
Structural phase transformations in quasicrystal-forming Al-Cu-Fe alloys and defects of the icosahedral phase
Authors:
Shalaeva, EV; Prekul, AF Author Full Names: Shalaeva, E. V.; Prekul, A. F.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 109 (4): 392-401 APR 2010
Abstract:
Transmission electron microscopy was used to investigate structural and phase transformations and defects of the icosahedral (iota) phase that is formed upon isothermal annealings (T (ann) = 550-700A degrees C) of quenched quasicrystal-forming alloys Al61Cu26Fe13 and Al63Cu25Fe12 (beta solid solution + iota phase). It has been established that in the Al63Cu25Fe12 alloy there occurs a reversible iota-R-approximant transformation, whereas in the Al61Cu26Fe13 alloy there is formed a single-phase iota structure with regions with a high density of randomly distributed planar defects (T (ann) = 550A degrees C), which are partially annealed at 650A degrees C. The observed defects are, mainly, ultrathin interlayers ("intergrowths" to 3-5 nm in thickness) on quasicrystal planes with A5(iota) axes with an imperfect decagonal structure. As the basic mechanism, the growth mechanism of the formation of defects during the beta -> i transformation is proposed. The role of the alloy composition and low-temperature beta -> 3C-phase transformation in the realization of this mechanism is discussed.
Title:
Charge and spin ordering in the mixed-valence compound LuFe2O4
Authors:
Harris, AB; Yildirim, T Author Full Names: Harris, A. B.; Yildirim, T.
Source:
PHYSICAL REVIEW B 81 (13): Art. No. 134417 APR 1 2010
Abstract:
Landau theory and symmetry considerations lead us to propose an explanation for several seemingly paradoxical behaviors of charge ordering (CO) and spin ordering (SO) in the mixed valence compound LuFe2O4. Both SO and CO are highly frustrated. We analyze a lattice gas model of CO within mean-field theory and determine the magnitude of several of the phenomenological interactions. We show that the assumption of a continuous phase transitions at which CO or SO develops implies that both CO and SO are incommensurate. To explain how ferroelectric fluctuations in the charge-disordered phase can be consistent with an antiferroelectric-ordered phase, we invoke an electron-phonon interaction in which a low-energy (20 meV) zone-center transverse phonon plays a key role. The energies of all the zone center phonons are calculated from first principles. We give a Landau analysis which explains SO and we discuss a model of interactions which stabilizes the SO state, if it is assumed commensurate. However, we suggest a high-resolution experimental determination to see whether this phase is really commensurate, as believed up to now. The applicability of representation analysis is discussed. A tentative explanation for the sensitivity of the CO state to an applied magnetic field in field-cooled experiments is given.
Title:
Sinusoidal magnetic structure in a three-dimensional antiferromagnetic Co-2(OH)AsO4: Incommensurate-commensurate magnetic phase transition
Authors:
de Pedro, I; Rojo, JM; Fernandez, JR; Fernandez-Diaz, MT; Rojo, T Author Full Names: de Pedro, I.; Rojo, J. M.; Rodriguez Fernandez, J.; Fernandez-Diaz, M. T.; Rojo, T.
Source:
PHYSICAL REVIEW B 81 (13): Art. No. 134431 APR 1 2010
Abstract:
Co-2(OH)AsO4 has been prepared by hydrothermal synthesis and characterized from x-ray and neutron powder diffraction. The structure consists of a three-dimensional framework in which Co(1)O-5-trigonal bi-pyramid dimers and Co(2)O-6-octahedra chains are simultaneously present. The magnetic structure has been determined by neutron (D2B and D1B) powder-diffraction data. Below 22 K, the Co-2(OH)AsO4 phase shows an incommensurate antiferromagnetic structure along the b direction. The propagation vector (0, delta, 0) is temperature dependent with a value of delta=0.430 at the lowest temperature (1.8 K). Magnetization measurements of Co-2(OH)AsO4 show a complex magnetic behavior with the presence of three different signals. Between 6 and 21 K, a strong dependence of the magnetic field is observed with a shift of the inflexion point associated to the three-dimensional antiferromagnetic ordered from 18 K at 1 kOe to 20.1 K at 90 kOe. The small sp! litting observed in the zero-field-cooled-field-cooled curves at low temperatures is characteristic of ferromagnetic interactions but saturation is not reached even up to 90 kOe. Heat-capacity measurements show an unusual dependence on the magnetic field for antiferromagnetic transitions with a jump at the Neel temperature quite small (2 J/Kmol). The magnetic contribution exhibits a lambda-type anomaly associated to the three-dimensional antiferromagnetic ordering. Surprisingly, the lambda anomaly grows with the magnetic field and becomes better defined. Neutron powder diffraction in different fields shows a magnetic phase transition. The incommensurate magnetic structure evolves at low temperatures toward a collinear AF phase for fields higher than 35 kOe.
Title:
Magnetic order of multiferroic ErMn2O5 studied by resonant soft x-ray Bragg diffraction
Authors:
Staub, U; Bodenthin, Y; Garcia-Fernandez, M; de Souza, RA; Garganourakis, M; Golovenchits, EI; Sanina, VA; Lushnikov, SG Author Full Names: Staub, U.; Bodenthin, Y.; Garcia-Fernandez, M.; de Souza, R. A.; Garganourakis, M.; Golovenchits, E. I.; Sanina, V. A.; Lushnikov, S. G.
Source:
PHYSICAL REVIEW B 81 (14): Art. No. 144401 APR 1 2010
Abstract:
Resonant magnetic soft x-ray diffraction is used to study the magnetic order of the Mn sublattices in multiferroic ErMn2O5. Data were collected at the Mn L-2,L-3 edges as a function of temperature, incident polarization, including the analysis of scattered polarizations for selected azimuths. The energy dependence of the magnetic reflections depends on the azimuthal angle in the commensurate magnetic (CM) ferroelectric (FE) phase, indicating different contributions to the scattering. In the incommensurate magnetic [two-dimensional (2D)-ICM] phase, the two observed reflections (1/2 +/- delta(x) 0 1/4+delta(z)) have distinct energy dependences too. Different origins of these differences in spectral shape are discussed. The azimuthal angle dependence at the L-3 edge can only be qualitatively described by a generalized magnetic model. The observed discrepancies may indicate the importance of magnetoelectric multipole scattering to these reflections. Reciprocal mesh scans show diffuse scattering along q and perpendicular to q as well as along the (h 0 0) direction in the CM phase. Diffuse scattering is also observed along (h 0 0) in the one-dimensional-ICM phase. At higher temperatures, in the 2D-ICM phase, the diffuse magnetic scattering is almost isotropic.
Title:
V-51 NMR study of the kagome staircase compound Ni3V2O8
Authors:
Ogloblichev, V; Kumagai, K; Verkhovskii, S; Yakubovsky, A; Mikhalev, K; Furukawa, Y; Gerashenko, A; Smolnikov, A; Barilo, S; Bychkov, G; Shiryaev, S Author Full Names: Ogloblichev, V.; Kumagai, K.; Verkhovskii, S.; Yakubovsky, A.; Mikhalev, K.; Furukawa, Yu.; Gerashenko, A.; Smolnikov, A.; Barilo, S.; Bychkov, G.; Shiryaev, S.
Source:
PHYSICAL REVIEW B 81 (14): Art. No. 144404 APR 1 2010
Abstract:
We used V-51 NMR to study magnetic ordering in the Ni3V2O8 single crystal with a Kagome staircase structure of Ni atoms. The NMR spectra were measured in the temperature range T= (3-300) K and magnetic fields H= (2-9.4) T directed along the main a, b, c axes of the orthorhombic (Cmca) crystal. The local magnetic field at the V-51 NMR probe determines position and the shape of the corresponding NMR line. These parameters yield an unique information, respectively, on the uniform and the staggered spin components of the ordered Ni. The NMR data collected at H >= 2 T are considered in line with predictions of the representation theory [A. Harris, Phys. Rev. B 76, 054447 (2007)] with a result that incommensurate amplitude-modulated structure of the spine Ni-s spins acquires in the high-temperature incommensurate (HTI) phase two prominent nearly equal spin components S-a approximate to S-c >> S-b instead of the longitudinal incommensurate spin-density wave (SDW) order with S-a >> S-c, S-b as it was deduced from neutron-diffraction data [M. Kenzelmann et al., Phys. Rev. B 74, 014429 (2006)]. No noticeable variation of SDW polarization in the ab plane was detected below the HTI-low-temperature incommensurate (LTI) transition. In both the HTI and LTI phases two almost equal spin components of the Ni-s spins S-a approximate to S-c >> S-b exist at H < 4.7 T. Their phasing is still not determined. The bulk magnetization in these phases is explained by contribution of the cross-tie Ni-c spins which antiferromagnetic structure in the LTI phase is canted along H.
Title:
Magnetic properties of EuPtSi3 single crystals
Authors:
Kumar, N; Dhar, SK; Thamizhavel, A; Bonville, P; Manfrinetti, P Author Full Names: Kumar, Neeraj; Dhar, S. K.; Thamizhavel, A.; Bonville, P.; Manfrinetti, P.
Source:
PHYSICAL REVIEW B 81 (14): Art. No. 144414 APR 1 2010
Abstract:
Single crystals of EuPtSi3, which crystallize in the BaNiSn3-type crystal structure, have been grown by high-temperature solution growth method using molten Sn as the solvent. EuPtSi3 which lacks the inversion symmetry and has only one Eu site in the unit cell is found to be an antiferromagnet with two successive magnetic transitions at T-N1=17 K and T-N2=16 K, as inferred from magnetic susceptibility, heat capacity, and Eu-151 Mossbauer measurements. The isothermal magnetization data for H parallel to[001] reveal a metamagnetic transition at a critical field H-c=1 T. The magnetization saturates to a moment value of 6.43 mu(B)/Eu above 5.9 T (9.2 T) for H parallel to[001] ([100]), indicating that these fields are spin-flip fields for the divalent Eu moments along the two axes. The origin of this anisotropic behavior is discussed. A magnetic (H and T) phase diagram has been constructed from the temperature dependence of isothermal magnetization data. The reduced jump in the heat capacity at T-N1 indicates a transition to an incommensurate, amplitude modulated antiferromagnetic structure. The shape of the hyperfine field split Mossbauer spectrum at T-N1 provides additional support for the proposed nature of this magnetic transition.
Title:
Incommensurate spin correlations induced by magnetic Fe ions substituted into overdoped Bi1.75Pb0.35Sr1.90CuO6+z
Authors:
Hiraka, H; Hayashi, Y; Wakimoto, S; Takeda, M; Kakurai, K; Adachi, T; Koike, Y; Yamada, I; Miyazaki, M; Hiraishi, M; Takeshita, S; Kohda, A; Kadono, R; Tranquada, JM; Yamada, K Author Full Names: Hiraka, H.; Hayashi, Y.; Wakimoto, S.; Takeda, M.; Kakurai, K.; Adachi, T.; Koike, Y.; Yamada, I.; Miyazaki, M.; Hiraishi, M.; Takeshita, S.; Kohda, A.; Kadono, R.; Tranquada, J. M.; Yamada, K.
Source:
PHYSICAL REVIEW B 81 (14): Art. No. 144501 APR 1 2010
Abstract:
Spin correlations in the overdoped region of Bi1.75Pb0.35Sr1.90CuO6+z have been explored with Fe-doped single crystals characterized by neutron scattering, muon-spin-rotation spectroscopy, and magnetic-susceptibility measurements. Static incommensurate spin correlations induced by the Fe spins are revealed by elastic neutron scattering. The resultant incommensurability delta is unexpectedly large (similar to 0.2 r.l.u.), as compared with delta similar to 1/8 in overdoped superconductor La2-xSrxCuO4. Intriguingly, the large delta in this overdoped region is close to the hole concentration p. This result is reminiscent of the delta approximate to p trend observed in underdoped La2-xSrxCuO4; however, it is inconsistent with the saturation of delta in the latter compound in the overdoped regime. While our findings in Fe-doped Bi1.75Pb0.35Sr1.90CuO6+z support the commonality of incommensurate spin correlations in high-T-c cuprate superconductors, they also s! uggest that the magnetic response might be dominated by a distinct mechanism in the overdoped region.
Title:
Phase diagram of H-2 adsorbed on graphene
Authors:
Gordillo, MC; Boronat, J Author Full Names: Gordillo, M. C.; Boronat, J.
Source:
PHYSICAL REVIEW B 81 (15): Art. No. 155435 APR 15 2010
Abstract:
The phase diagram of the first layer of H-2 adsorbed on top of a single graphene sheet has been calculated by means of a series of diffusion Monte Carlo simulations. We have found that, as in the case of He-4, the ground state of molecular hydrogen is a root 3 x root 3 commensurate structure, followed, upon a pressure increase, by an incommensurate triangular solid. A striped phase of intermediate density was also considered and found lying on top of the equilibrium curve separating both commensurate and incommensurate solids.
Title:
Periodic step arrays on the aperiodic i-Al-Pd-Mn quasicrystal surface at high temperature
Authors:
Sato, Y; Unal, B; Lograsso, TA; Thiel, PA; Schmid, AK; Duden, T; Bartelt, NC; McCarty, KF Author Full Names: Sato, Y.; Unal, B.; Lograsso, T. A.; Thiel, P. A.; Schmid, A. K.; Duden, T.; Bartelt, N. C.; McCarty, K. F.
Source:
PHYSICAL REVIEW B 81 (16): Art. No. 161406 APR 15 2010
Abstract:
We have observed the configuration and motion of surface steps on the aperiodic icosahedral (i-) Al-Pd-Mn quasicrystal using low-energy electron microscopy and scanning tunneling microscopy. As the quasicrystal is cooled from high temperature, bulk vacancies migrate to the surface causing the surface to be etched. Surprisingly, this etching occurs by two types of steps with different heights moving in different directions with different velocities. The steady-state surface morphology is a uniformly spaced rhomboidal step network. This network requires that the layer stacking near the surface deviates from the bulk quasicrystal stacking.
Title:
Quantum critical behavior of antiferromagnetic itinerant systems with van Hove singularities
Authors:
Katanin, A Author Full Names: Katanin, A.
Source:
PHYSICAL REVIEW B 81 (16): Art. No. 165118 APR 15 2010
Abstract:
The interplay of magnetic and superconducting fluctuations in two-dimensional systems with van Hove singularities in the electronic spectrum is considered within the functional renormalization-group (fRG) approach. While the fRG flow has to be stopped at a certain minimal temperature T-RG(min), we study temperature dependence of magnetic and superconducting susceptibilities below T-RG(min) to obtain the crossover temperatures to the regime with strong magnetic and superconducting fluctuations. Near half filling we obtain the largest crossover temperature, corresponding to a regime with strong commensurate magnetic fluctuations, which is replaced by a regime with strong incommensurate fluctuations further away from half filling. With further decreasing density the system undergoes quantum phase transition from incommensurate to paramagnetic phase. Similarly to results of Hertz-Moriya-Millis approach, the temperature dependence of the inverse (in-commensurate) magnetic susceptibility at the magnetic quantum-critical point is found almost linear in temperature.
Title:
Classification and Interpretation of the Polarization of Multiferroic RMn2O5
Authors:
Fukunaga, M; Noda, Y Author Full Names: Fukunaga, Mamoru; Noda, Yukio
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (5): Art. No. 054705 MAY 2010
Abstract:
We have collected and compared temperature-dependent polarization data of multiferroic RMn2O5 for 11 kinds of rare earths (R) from the literature and our own measurements. Although the reported data are inconsistent, it was found that the maximum polarization values for R = Y, Dy, Ho, Er, and Tm are almost equal above 30 K except for the phase transition temperature where the polarization disappears. The findings suggest a standard polarization value for RMn2O5 of 100-120 nC/cm(2) at 30 K in a commensurate magnetic (CM) phase. We discuss the nature and issues of the measured polarization of RMn2O5 from the data and our detailed measurement results for YMn2O5. Temperature-dependent ferroelectric hysteresis loops of YMn2O5 by the double-wave method reveal that an antiferroelectric-like high-temperature incommensurate magnetic (ICM) phase and a ferroelectric low-temperature ICM phase, while the intermediate CM phase is ferrielectric.
Title:
Microstructural and mechanical study of an Al matrix composite reinforced by Al-Cu-Fe icosahedral particles
Authors:
Laplanche, G; Joulain, A; Bonneville, J; Gauthier-Brunet, V; Dubois, S; El Kabir, T Author Full Names: Laplanche, Guillaume; Joulain, Anne; Bonneville, Joel; Gauthier-Brunet, Veronique; Dubois, Sylvain; El Kabir, Tarik
Source:
JOURNAL OF MATERIALS RESEARCH 25 (5): 957-965 MAY 2010
Abstract:
In this study, we produced an Al matrix composite material reinforced by Al-Cu-Fe particles of the icosahedral phase. The composite material was prepared using a hot isostatic pressure technique at T = 673 K and P = 180 MPa. The mechanical properties were investigated by compression tests performed at constant strain rate over the temperature range 290-823 K. The results show a vigorous strengthening effect resulting from the reinforcement particles. Strengthening is attributed to two main contributions arising from load transfer between the Al matrix and the reinforcement particles and from plastic deformation of the Al grains. The present results are compared with those obtained in a previous work on an Al-based composite reinforced by Al-Cu-Fe particles of the omega-tetragonal phase.

Update: 6-May-2010

Title:
Structural and magnetic modulations in CaCuxMn7-xO12
Authors:
Slawinski, W; Przenioslo, R; Sosnowska, I; Bieringer, M Author Full Names: Slawinski, W.; Przenioslo, R.; Sosnowska, I.; Bieringer, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (18): Art. No. 186001 MAY 12 2010
Abstract:
Low temperature atomic position modulations and magnetic moment modulations are reported for CaCuxMn7-xO12 (x = 0.0, 0.1 and 0.23) using neutron powder diffraction. Both modulations are described with propagation vectors (0, 0, q) parallel to the c-axis in the hexagonal setting. The present neutron diffraction studies confirm the quantitative model describing the atomic position modulations in CaCuxMn(7-x)O(12) (x = 0.0 and 0.1) as derived from synchrotron based powder x-ray diffraction studies (Slawinski et al 2009 Acta Crystallogr. B 65 535). Neutron diffraction studies confirm the relation between the atomic position modulation length L-p and the magnetic modulation length L-m = 2L(p) between 50 K and the Neel temperature T-N. CaCuxMn(7-x)O(12) (x = 0.1 and 0.23) shows a magnetic phase transition near 50 K associated with considerable changes of the magnetic modulation length and the magnetic coherence length, similar to that observed in the parent CaMn7O12.
Title:
Magnetic properties of Bi(Fe1-x M (x) )O-3 (M = Mn, Ti)
Authors:
Troyanchuk, IO; Chobot, AN; Mantytskaya, OS; Tereshko, NV Author Full Names: Troyanchuk, I. O.; Chobot, A. N.; Mantytskaya, O. S.; Tereshko, N. V.
Source:
INORGANIC MATERIALS 46 (4): 424-428 APR 2010
Abstract:
The magnetic properties of Bi(Fe1 - x M (x) )O-3(M = Mn, Ti) solid solutions have been studied in magnetic fields of up to 11.2 x 10(3) kA/m, and the composition stability range of the R3c ferroelectric phase has been determined. The results indicate that partial Ti4+ substitution for Fe3+ leads to a transition from a modulated antiferromagnetic state to a homogeneous weakly ferromagnetic ferroelectric state (x = 0.08), whereas the Bi(Fe (1-x) (3+) Mn (x) (3+) )O-3 solid solutions do not exhibit weak ferromagnetism. Charge compensation in is assumed to be ensured by cation vacancies.
Title:
Short-range magnetic order, irreversibility and giant magnetoresistance near the triple points in the (x, T) magnetic phase diagram of ZrMn6Sn6-xGax
Authors:
Mazet, T; Ihou-Mouko, H; Mareche, JF; Malaman, B Author Full Names: Mazet, T.; Ihou-Mouko, H.; Mareche, J. -F.; Malaman, B.
Source:
EUROPEAN PHYSICAL JOURNAL B 74 (4): 487-497 APR 2010
Abstract:
We have studied pseudo-layered ZrMn6Sn6-xGax intermetallics (0.55 a parts per thousand currency sign x a parts per thousand currency sign 0.81) using magnetic, magnetoresistivity and powder neutron diffraction measurements. All the alloys studied have magnetic ordering temperatures in the 450-490 K temperature range. They present complex temperature-dependent partially disordered magnetic structures whose ferromagnetic component develops upon increasing the Ga content. ZrMn6Sn6-xGax alloys with x a parts per thousand currency sign 0.69 are essentially collinear antiferromagnets at high-temperature and adopt antifan-like arrangements at low temperature. For x a parts per thousand yen 0.75, the alloys order ferromagnetically and evolve to a fan-like structure upon cooling. The intermediate compositions (x = 0.71 and 0.73) present a canted fan-like order at high temperature and another kind of antifan-like arrangement at low temperature. The degree of short-range order tends to increase upon approaching the intermediate compositions. The (x, T) phase diagram contains two triple points (x similar to 0.70; T similar to 460 K and x similar to 0.74; T similar to 455 K), where the paramagnetic, an incommensurate and a commensurate phases meet, which possess some of the features of Lifshitz point. Irreversibilities manifest in the low-temperature magnetization curves at the antifan-fan or fan-ferromagnetic boundaries as well as inside the fan region. Giant magnetoresistance is observed, even above room temperature.
Title:
Elastic analysis of an elliptic notch in quasicrystals of point group 10 subjected to shear loading
Authors:
Li, LH Author Full Names: Li Lian-He
Source:
CHINESE PHYSICS B 19 (4): Art. No. 046101 APR 2010
Abstract:
Based on the stress potential and complex variable function method, this paper makes an elastic analysis of an elliptic notch subjected to uniform shear stress at infinity in quasicrystals with point group 10. With the aid of conformal transformation, an exact solution for the elliptic notch of the quasicrystals is obtained. The solution of the mode II Griffith crack as a special case is constructed. The stress intensity factor and energy release rate have been also obtained as a direct result of the crack solution.
Title:
Magnetization plateau and incommensurate spin modulation in Ca3Co2O6
Authors:
Zhao, Y; Gong, SS; Li, W; Su, G Author Full Names: Zhao, Yang; Gong, Shou-Shu; Li, Wei; Su, Gang
Source:
APPLIED PHYSICS LETTERS 96 (16): Art. No. 162503 APR 19 2010
Abstract:
The magnetic properties of a trigonal prism unit of the spin-2 frustrated compound Ca3Co2O6 are studied by means of the density-matrix renormalization group method. A magnetization plateau at m(s)/3 (m(s) is the saturation magnetization) with ferrimagnetic structure is observed. By fitting the experimental data of magnetic curve, an estimation of the couplings gives J(1)=-26.84 K, J(2)=0.39 K, and J(3)=0.52 K. The local magnetic moments are unveiled to exhibit an incommensurate sinusoidally modulation along the three chains of the trigonal prism, which gives a strong theoretical support to the experimentally observed incommensurate partially disordered antiferromagnetic state for Ca3Co2O6. The present result suggests that the modulation indeed originates from the competition of antiferromagnetic and ferromagnetic couplings. (C) 2010 American Institute of Physics. [doi:10.1063/1.3413931]
Title:
OXIDATION BEHAVIOR OF THE PHASE ICOSAEDRAL QUASICRISTAL Al-62,Al- 2 Cu-25,Cu-3 Fe-12,Fe-5
Authors:
Nascimento, L; Agostinho, LCL; Cavalcanti, BF Author Full Names: Nascimento, L.; Agostinho, L. C. L.; Cavalcanti, B. F.
Source:
ACTA MICROSCOPICA 18 (3): 295-303 2009
Abstract:
Oxidation behavior of the quasicrystalline alloy with nominal composition Al-62,Al- 2 Cu-25,Cu-3 Fe-12,Fe-5 was analyzed under different conditions of duration of thermal treatment. It was used X - Ray Diffratometry to follow the alloy phases evolution and Scanning Electron Microscopy (SEM) to analyze the quasicrystal morphology and oxidation. Below 750 degrees C the alloy shows intermetallic phases with associations of the alloy elements and above 675 degrees C the crystalline phase is stable. In icosahedral phase, aluminum oxidation forms a dense passivating layer at the outmost surface of the quasicrystal which causes depletion in both copper and iron. In the dense layer it was observed not only the presence of alumina, gamma - Al2O3, but also the formation of hematite.

Update: 15-Apr-2010

Title:
Microstructures and Phase Transformation of Al-Rased composite materials Reinforced by Al-Cu-Co Decagonal Quasicrystalline Particles
Authors:
Zhu, M; Yang, GC; Cheng, SL; Wang, BH; Zhou, YH Author Full Names: Zhu Man; Yang Gencang; Cheng Suling; Wang Binghui; Zhou Yaohe
Source:
RARE METAL MATERIALS AND ENGINEERING 38 (9): 1584-1588 SEP 2009
Abstract:
Al65Cu15Co20 decagonal quasicrystalline alloys were prepared by an arc-melting furnace. The aluminium-based composites were fabricated by using the Al65Cu15Co20 decagonal quasicrystalline particles as reinforcing phase and Al-4.5 wt%Cu alloy as matrix with mechanical stirring. The microstructures, the phase composition, and the distribution of Al65Cu15Co20 were characterisied by XRD, SEM, SEM and EDS for the Al65Cu15Co20 quasicrystalline alloys and the reinforced composites. And the morphology, chemical composition and structure changes of the quasicrystalline particles before and after adding to the melt were also analysised. As the interdiffusion occurs between the quasicrystalline particles and the melt, the quasicrystalline particles can not exist stably in the melt. The morphology of the particles turns from inregular polygons to block and lath-like in shape as following: D-Al62.10Cu17.46Co20.44 -> theta-Al79.55Cu1.10Co19.32 after adding the quasicrystalline particles into the melt. During the solidification process, the theta phase distributes uniformly along the grain boundaries because of the "interfacial pushing effect".
Title:
Evidence for a Magnetically Driven Superconducting Q Phase of CeCoIn5
Authors:
Kenzelmann, M; Gerber, S; Egetenmeyer, N; Gavilano, JL; Strassle, T; Bianchi, AD; Ressouche, E; Movshovich, R; Bauer, ED; Sarrao, JL; Thompson, JD Author Full Names: Kenzelmann, M.; Gerber, S.; Egetenmeyer, N.; Gavilano, J. L.; Straessle, Th; Bianchi, A. D.; Ressouche, E.; Movshovich, R.; Bauer, E. D.; Sarrao, J. L.; Thompson, J. D.
Source:
PHYSICAL REVIEW LETTERS 104 (12): Art. No. 127001 MAR 26 2010
Abstract:
We have studied the magnetic order inside the superconducting phase of CeCoIn5 for fields along the [1 0 0] crystallographic direction using neutron diffraction. We find a spin-density wave order with an incommensurate modulation Q = (q, q, 1/2) and q = 0.45(1), which within our experimental uncertainty is indistinguishable from the spin-density wave found for fields applied along [1 - 10]. The magnetic order is thus modulated along the lines of nodes of the d(x2-y2) superconducting order parameter, suggesting that it is driven by the electron nesting along the superconducting line nodes. We postulate that the onset of magnetic order leads to reconstruction of the superconducting gap function and a magnetically induced pair density wave.
Title:
Incommensurate spin-density-wave order in quasi-one-dimensional metallic antiferromagnet NaV2O4
Authors:
Nozaki, H; Sugiyama, J; Mansson, M; Harada, M; Pomjakushin, V; Sikolenko, V; Cervellino, A; Roessli, B; Sakurai, H Author Full Names: Nozaki, Hiroshi; Sugiyama, Jun; Mansson, Martin; Harada, Masashi; Pomjakushin, Vladimir; Sikolenko, Vadim; Cervellino, Antonio; Roessli, Bertrand; Sakurai, Hiroya
Source:
PHYSICAL REVIEW B 81 (10): Art. No. 100410 MAR 2010
Abstract:
To clarify the reason for the coexistence of long-range antiferromagnetic order and metallic conductivity for NaV2O4, in which the V ions form quasi-one-dimensional zigzag chains along the b axis, we have performed a neutron-scattering experiment using a powder sample down to 20 K. The analysis of the magnetic powder diffractogram below T-N=140 K demonstrates the formation of an incommensurate spin-density-wave order with k=(0,0.191,0); the ordered moment was estimated as (0,0,0.77 mu(B)) at 20 K.
Title:
Valence band structure of the icosahedral Ag-In-Yb quasicrystal
Authors:
Sharma, HR; Simutis, G; Dhanak, VR; Nugent, PJ; Cui, C; Shimoda, M; McGrath, R; Tsai, AP; Ishii, Y Author Full Names: Sharma, H. R.; Simutis, G.; Dhanak, V. R.; Nugent, P. J.; Cui, C.; Shimoda, M.; McGrath, R.; Tsai, A. P.; Ishii, Y.
Source:
PHYSICAL REVIEW B 81 (10): Art. No. 104205 MAR 2010
Abstract:
The valence band structure of the icosahedral (i) Ag-In-Yb quasicrystal, which is isostructural to the binary i-Cd-Yb system, is investigated by ultraviolet photoemission spectroscopy (UPS). Experimental results are compared with electronic-structure calculations of a cubic approximant of the same phase. UPS spectra from the fivefold, threefold, and twofold i-Ag-In-Yb surfaces reveal that the valence band near to the Fermi level is dominated by Yb 4f-derived states, in agreement with calculations. The spectra also exhibit peaks which are surface core level shifted, caused by changes in the electronic structure in surface layers. Calculations yield a pseudogap in the density of states due to a hybridization of the Yb 5d band with the Ag 5p and In 5p bands. Both experimental and calculated band features are very similar to those of Cd-Yb. The modification of the band structure after surface treatment by sputtering and by oxidation is also studied. Additionally, the work ! function of i-Ag-In-Yb measured from the width of UPS spectrum is found to be almost unaffected by surface orientation, but increases after sputtering or oxidation.
Title:
Static and dynamical susceptibility of LaO1-xFxFeAs
Authors:
Monni, M; Bernardini, F; Profeta, G; Sanna, A; Sharma, S; Dewhurst, JK; Bersier, C; Continenza, A; Gross, EKU; Massidda, S Author Full Names: Monni, M.; Bernardini, F.; Profeta, G.; Sanna, A.; Sharma, S.; Dewhurst, J. K.; Bersier, C.; Continenza, A.; Gross, E. K. U.; Massidda, S.
Source:
PHYSICAL REVIEW B 81 (10): Art. No. 104503 MAR 2010
Abstract:
The mechanism of superconductivity and magnetism and their possible interplay have recently been under debate in pnictides. A likely pairing mechanism includes an important role of spin fluctuations and can be expressed in terms of the magnetic susceptibility chi. The latter is therefore a key quantity in the determination of both the magnetic properties of the system in the normal state and of the contribution of spin fluctuations to the pairing potential. A basic ingredient to obtain chi is the independent-electron susceptibility chi(0). Using LaO1-xFxFeAs as a prototype material, in this report we present a detailed ab initio study of chi(0)(q, omega) as a function of doping and of the internal atomic positions. The resulting static chi(0)(q, 0) is consistent with both the observed M-point-related magnetic stripe phase in the parent compound and with the existence of incommensurate magnetic structures predicted by ab initio calculations upon doping.
Title:
Structure of the (010) surface of the orthorhombic complex metallic alloy T-Al-3(Mn,Pd)
Authors:
Deniozou, T; Addou, R; Shukla, AK; Heggen, M; Feuerbacher, M; Krajci, M; Hafner, J; Widmer, R; Groning, O; Fournee, V; Dubois, JM; Ledieu, J Author Full Names: Deniozou, Th.; Addou, R.; Shukla, A. K.; Heggen, M.; Feuerbacher, M.; Krajci, M.; Hafner, J.; Widmer, R.; Groening, O.; Fournee, V.; Dubois, J. -M.; Ledieu, J.
Source:
PHYSICAL REVIEW B 81 (12): Art. No. 125418 MAR 2010
Abstract:
The atomic and electronic structures of the (010) surface of the T-Al-3(Mn,Pd) complex metallic alloy is investigated by means of low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), x-ray photoelectron diffraction (XPD), and ab initio calculations. While structural imperfections are observed at the surface and out of the various possible terminations, the puckered P2 layer is identified as the only surface termination, thus pointing out the existence of a well-defined minimum in the surface energy landscape. The measured step heights correspond to distances between identical planes along the [010] direction in the bulk model, i.e., b/2. A bias dependency of the STM topography is found. The XPD and LEED patterns confirm the pseudotenfold symmetry of the sample. XPS and UPS show a more metallic signature of the T phase compared to Al-based quasicrystalline phases.
Title:
Incommensurate magnetic order and phase separation in the two-dimensional Hubbard model with nearest- and next-nearest-neighbor hopping
Authors:
Igoshev, PA; Timirgazin, MA; Katanin, AA; Arzhnikov, AK; Irkhin, VY Author Full Names: Igoshev, P. A.; Timirgazin, M. A.; Katanin, A. A.; Arzhnikov, A. K.; Irkhin, V. Yu.
Source:
PHYSICAL REVIEW B 81 (9): Art. No. 094407 MAR 1 2010
Abstract:
We consider the ground-state magnetic phase diagram of the two-dimensional Hubbard model with nearest- and next-nearest-neighbor hopping in terms of electronic density and interaction strength. We treat commensurate ferromagnetic and antiferromagnetic as well as incommensurate (spiral) magnetic phases. The first-order magnetic transitions with changing chemical potential, resulting in a phase separation (PS) in terms of density, are found between ferromagnetic, antiferromagnetic, and spiral magnetic phases. We argue that PS has a dramatic influence on the phase diagram in the vicinity of half-filling. The results imply possible interpretation of the unusual behavior of magnetic properties of single-layer cuprates in terms of PS between collinear and spiral magnetic phases. The relevance of our results to the magnetic properties of the ruthenates is also discussed.
Title:
Single magnetic chirality in the magnetoelectric NdFe3((BO3)-B-11)(4)
Authors:
Janoschek, M; Fischer, P; Schefer, J; Roessli, B; Pomjakushin, V; Meven, M; Petricek, V; Petrakovskii, G; Bezmaternikh, L Author Full Names: Janoschek, M.; Fischer, P.; Schefer, J.; Roessli, B.; Pomjakushin, V.; Meven, M.; Petricek, V.; Petrakovskii, G.; Bezmaternikh, L.
Source:
PHYSICAL REVIEW B 81 (9): Art. No. 094429 MAR 1 2010
Abstract:
We have performed an extensive study of single crystals of the magnetoelectric NdFe3 ((BO3)-B-11)(4) by means of a combination of single-crystal neutron diffraction and spherical neutron polarimetry. Our investigation did not detect significant deviations at low temperatures from space group R32 concerning the chemical structure. With respect to magnetic ordering our combined results demonstrate that in the commensurate magnetic phase below T-N approximate to 30 K all three magnetic Fe moments and the magnetic Nd moment are aligned ferromagnetically in the basal hexagonal plane but align antiferromagnetically between adjacent planes. The phase transition to the low-temperature incommensurate (IC) magnetic structure observed at T-IC approximate to 13.5 K appears to be continuous. By means of polarized neutron studies it could be shown that in the incommensurate magnetic phase the magnetic structure of NdFe3((BO3)-B-11)(4) is transformed into a long-period antiferromagnetic helix with single chirality. Close to the commensurate-incommensurate phase transition third-order harmonics were observed, which in addition indicate the formation of magnetic solitons.
Title:
Theoretical studies of the incommensurate magnetic structure of a heavy fermion system: CeRhIn5
Authors:
Bjorkman, T; Lizarraga, R; Bultmark, F; Eriksson, O; Wills, JM; Bergman, A; Andersson, PH; Nordstrom, L Author Full Names: Bjorkman, Torbjorn; Lizarraga, Raquel; Bultmark, Fredrik; Eriksson, Olle; Wills, John M.; Bergman, Anders; Andersson, Per H.; Nordstrom, Lars
Source:
PHYSICAL REVIEW B 81 (9): Art. No. 094433 MAR 1 2010
Abstract:
We have investigated the electronic structure and the incommensurate magnetic configuration of the pressure-induced superconductor CeRhIn5. Noncollinear first-principles calculations were performed in the local-density approximation plus U scheme. The observed magnetic configuration is described accurately in our calculations, especially considering the minute energy scale which is relevant (microelectron volt). The band structure and Fermi surfaces were investigated and nesting was found to be responsible for the complex noncollinear magnetic state of CeRhIn5.
Title:
Surface plasmon enhanced transmission through gold planar crystals with various aperture arrangements
Authors:
Xue, J; Dong, BQ; Wang, X; Yang, R; Xu, ZC; Chen, YF; Huq, E; Zeng, W; Qu, XP; Liu, R Author Full Names: Xue, Jing; Dong, Bi-Qin; Wang, Xu; Yang, Rong; Xu, Zhen-Cheng; Chen, Yifang; Huq, Ejaz; Zeng, Wei; Qu, Xin-Ping; Liu, Ran
Source:
MICROELECTRONIC ENGINEERING 87 (5-8): 1340-1343 MAY-AUG 2010
Abstract:
Various planar crystals in gold films are fabricated by focused ion beam (FIB) technique. We theoretically and experimentally show that the enhanced transmission through the planar crystals is dependent on the nanoaperture's arrangement and this extraordinary transmission can be attributed to the excitation of surface plasmon polaritons (SPPs) on the metal-air interface. In contrast to other crystals, the quasicrystal exhibits broadband plasmonic resonances. Near-field optical images provide direct evidence for surface plasmon-mediated enhanced transmission in a wide wavelength range through the gold quasicrystal. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Study of Biological Effect of MC3T3-E1 in vitro by A Novel 2.4GHz Radiofrequency Electromagnetic Field Exposure System
Authors:
Cherng, S; Teng, HC Author Full Names: Cherng, Shen; Teng, Hsien-Chiao
Source:
LIFE SCIENCE JOURNAL-ACTA ZHENGZHOU UNIVERSITY OVERSEAS EDITION 6 (4): 41-49 2009
Abstract:
A 2.4GHz mobile-phone/blue-tooth radiofrequency electromagnetic field (RF-EMF) exposure system for cellular experiment MC3T3-E1 in vitro was designed to study the biological effects and demonstrated in this report. Experimental results have illustrated the observation of signal at 14Hz through algorithm analysis of the measured near field magnetic fluctuation and the modulation of gap junction intercellular communication (GJIC) within mouse osteoblast cells (MC3T3-E1) under RF-EMF power density at 0.3mWatt/cm(2). [Life Science Journal. 2009; 6(4): 41 49] (ISSN: 1097-8135).
Title:
Influence of cooling rate and cerium addition on rapidly solidified Al-TM alloys
Authors:
Michalcova, A; Vojtech, D; Schumacher, G; Novak, P; Klementova, M; Serak, J; Mudrova, M; Valdaufova, J Author Full Names: Michalcova, A.; Vojtech, D.; Schumacher, G.; Novak, P.; Klementova, M.; Serak, J.; Mudrova, M.; Valdaufova, J.
Source:
KOVOVE MATERIALY-METALLIC MATERIALS 48 (1): 1-7 2010
Abstract:
Rapidly solidified alloys, based on an aluminium-transition metal (TM) system, are promising structural materials. They show good mechanical properties and excellent thermal stability, which is caused by the very fine nanostructure of these materials and by the presence of nonequilibrium intermetallic phases. Influence of the cooling rate and Ce addition on properties of Al-5.5Ce-3Fe-1.5Ti alloy that was prepared by the melt spinning method was studied in this work. It was shown that formation of the quasicrystalline phase depends on the cooling rate during melt spinning. The addition of a few weight percents of Ce modifies phase composition of the alloy and stabilizes quasicrystals at elevated temperatures. However, the influence of Ce addition on hardness was not observed.
Title:
Anisotropic Thermal Diffusivity and Conductivity of La-Doped Strontium Niobate Sr2Nb2O7
Authors:
Sparks, TD; Fuierer, PA; Clarke, DR Author Full Names: Sparks, Taylor D.; Fuierer, Paul A.; Clarke, David R.
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY 93 (4): 1136-1141 APR 2010
Abstract:
The thermal diffusivity of the La-doped layered perovskite Sr2Nb2O7 parallel and perpendicular to the perovskite layers is reported from room temperature up to 1000 degrees C. The anisotropy persists through an incommensurate-normal ferroelectric phase transformation at 215 degrees C and up to 1000 degrees C, the maximum temperature of our measurements. The thermal conductivity perpendicular to the perovskite layers, derived from the diffusivity in the same direction, calculated using the density and measured heat capacity, has a constant value of 1.05 +/- 0.05 W/mK up to 1000 degrees C. Possible explanations for the low thermal conductivity and anisotropy are described.
Title:
Structurally complex metallic coatings in the Al-Cu system and their orientation relationships with an icosahedral quasicrystal
Authors:
Duguet, T; Kenzari, S; Demange, V; Belmonte, T; Dubois, JM; Fournee, V Author Full Names: Duguet, Thomas; Kenzari, Samuel; Demange, Valerie; Belmonte, Thierry; Dubois, Jean-Marie; Fournee, Vincent
Source:
JOURNAL OF MATERIALS RESEARCH 25 (4): 764-772 APR 2010
Abstract:
Quasicrystals have been identified as alloys possessing unusually low surface energy. This results in poor adhesion properties of quasicrystalline coatings when deposited on metallic substrates, hindering the development of these new materials for technological applications. Here we investigate the possible use of complex Al-Cu metallic phases as interface layers to accommodate the structural and electronic mismatch between a quasicrystalline coating and a metallic substrate and improve adhesion. First, we show that all stable low-temperature phases of the Al-Cu system can be grown as thin films using DC magnetron sputtering. Among the various possible phases, we select the gamma-brass gamma-Al4Cu9 as a promising candidate for the interface layer. Then the gamma-Al4Cu9 phase is grown on the fivefold surface of an icosahedral (i-) Al-Pd-Mn quasicrystal. The interface is investigated by transmission electron microscopy and shows a clear texturing of the film. The gra! ins exhibit rotational epitaxy with the substrate. We find that the interface is mainly composed of a beta-phase of unknown chemical composition and sometimes exhibits gamma grains in direct contact with the quasicrystalline substrate. Occasionally, we observe a fourth phase at the beta/gamma interface, identified as beta(1), possessing a lattice parameter a(beta 1) equal to 2a(beta) and 2/3a(gamma).
Title:
The effect of thermal treatment on the magnetic state and cluster-related disorder of icosahedral Al-Pd-Mn quasicrystals
Authors:
Jaglicic, Z; Jagodic, M; Grushko, B; Zijlstra, ES; Weber, T; Steurer, W; Dolinsek, J Author Full Names: Jaglicic, Z.; Jagodic, M.; Grushko, B.; Zijlstra, E. S.; Weber, Th.; Steurer, W.; Dolinsek, J.
Source:
INTERMETALLICS 18 (4): 623-632 APR 2010
Abstract:
The evolution of the magnetic state and the cluster-related disorder upon thermal treatment of the icosahedral i-Al-Pd-Mn quasicrystals were studied on single-crystalline samples subjected to different thermal annealing sequences involving short and long annealing times and slow or fast cooling modes. In this way, thermal equilibration of the samples was systematically changed by varying the amount of vacancies and thermal strains. The results show that different thermal treatments can reduce or increase reversibly the paramagnetic magnetization of the i-Al-Pd-Mn samples of nominally the same composition by a factor up to 26. Magnetic susceptibility and magnetization measurements have demonstrated comparable importance of the vacancies and thermal strains on the size of the mean effective magnetic moment per Mn atom. While the reduced vacancy concentration reduces the mean effective moment, thermal strains induced by rapid cooling increase it. Theoretical ab-initio calculations of the effect of vacancies and thermal strains on the magnetic properties of a periodic approximant model to the i-Al-Pd-Mn phase predict that vacancies at specific Al sites introduce magnetic moments at the Mn sites, which are otherwise nonmagnetic in the perfect structure. Removal of thermal strains by relaxation of the structure containing vacancies acts in the opposite way by decreasing the moments. X-ray diffraction experiments with full reciprocal space sampling revealed that the cluster-related disorder cannot be improved noticeably by annealing at either 800 degrees C or 600 degrees C even for annealing times as long as three months, suggesting that this disorder may be intrinsic to the i-Al-Pd-Mn phase, needed for the electronic or entropic stabilization of the structure. (C) 2009 Elsevier Ltd. All rights reserved.
Title:
NEPHELINE: STRUCTURE OF THREE SAMPLES FROM THE BANCROFT AREA, ONTARIO, OBTAINED USING SYNCHROTRON HIGH-RESOLUTION POWDER X-RAY DIFFRACTION
Authors:
Antao, SM; Hassan, I Author Full Names: Antao, Sytle M.; Hassan, Ishmael
Source:
CANADIAN MINERALOGIST 48 (1): 69-80 FEB 2010
Abstract:
The crystal structure of three samples of nepheline (ideally, K2Na6[Al8Si8O32]) from the Bancroft area of Ontario (1a, b: Egan Chute, 2: Nephton, and 3: Davis Hill), each with different types of superstructure reflections, has been studied using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinement. The samples have different origins. The structure was refined in space group P6(3). The R-F(2) index, number of unique observed reflections, pseudohexagonal subcell parameters, and site-occupancy factor (sof) for the K site are as follows: Sample 1b: R-F(2) = 0.0433, N-obs = 1399, a = 9.99567(1), c = 8.37777(1) angstrom, V = 724.907(2) angstrom(3), and K (sof) = 0.716(1). Sample 2: R-F(2) = 0.0669, N-obs = 1589, a = 10.00215(1), c = 8.38742(1) angstrom, V = 726.684(1) angstrom(3), and K (sof) = 0.920(1). Sample 3: R-F(2) = 0.0804, N-obs = 1615, a = 9.99567(1), c = 8.37873(1) angstrom, V = 724.991(1) angstrom(3), and K (sof) = 0.778(2). Sample 2 has the largest sof for K and the largest volume. The satellite reflections in the three nepheline samples were observed in the HRPXRD traces and give rise to different incommensurate superstructures. The Al and Si atoms in the T-3 and T-4 sites are ordered differently in the three samples, which may indicate the presence of a domain structure based on Al-Si order. The positions for the Al and Si atoms were interchanged in two samples because of the resulting < T-O > distances. The slight excess of Si over Al atoms, characteristically encountered in well-analyzed samples of nepheline, is reflected in the < T-O > distances.
Title:
The incommensurately modulated structures of natural natrite at 120 and 293 K from synchrotron X-ray data
Authors:
Arakcheeva, A; Bindi, L; Pattison, P; Meisser, N; Chapuis, G; Pekov, I Author Full Names: Arakcheeva, Alla; Bindi, Luca; Pattison, Philip; Meisser, Nicolas; Chapuis, Gervais; Pekov, Igor
Source:
AMERICAN MINERALOGIST 95 (4): 574-581 APR 2010
Abstract:
The incommensurately modulated structure of the mineral natrite has been refined for the first time. Two single-crystal grains, Lv and Kh, from two different occurrences [Mt. Karnasurt, Lovozero massif (Lv), Kola peninsula, Russia, and the pegmatite of Mt. Koashva, Khibiny massif (Kh)], have been investigated at 293 and 120 K using synchrotron X-ray data. The average structures of both minerals are identical and the basic features of the structural modulations are similar to the synthetic gamma-Na2CO3 phase previously published. The gamma (incommensurate) -> delta (lock-in) phase transition reported at low temperature for the synthetic compound was not observed down to 120 K in natural natrite. Crystal-chemical aspects, especially about the second coordination sphere for the carbon atoms, are examined to explain the different structural behaviors observed at low temperature. The possible role played by the minor isomorphous substitutions in natural na! trite specimens is also discussed.

Update: 8-Apr-2010

Title:
Structural investigation of composite phases Ba1+x[(NaxMn1-x)O-3] with x similar or equal to 2/7, 5/17 and 1/3; exotic Mn4.5+ valence
Authors:
Roussel, P; Perez, O; Quarez, E; Leligny, H; Mentre, O Author Full Names: Roussel, Pascal; Perez, Olivier; Quarez, Eric; Leligny, Henri; Mentre, Olivier
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 225 (1): 1-11 2010
Abstract:
Structural models are proposed for three composite compounds of chemical formula Ba1+x[(NaxMn1-x)O-3] (x similar or equal to 2/7, 5/17 and 1/3) by single crystal X-ray diffraction; superspace formalism is used to obtain an unified description of the three phases. The modulation affecting Ba atoms can be easily designed but the competition "occupational/displacive" modulations relating to the Mn/Na metallic columns were particularly difficult to modelize. However, the large amplitude of the displacive modulation affecting the oxygen atoms (similar or equal to +/- 0.7 angstrom) in comparison with that observed for related compounds (similar or equal to +/- 0.3 angstrom) makes it a direct consequence of the Na+ alkali insertion inside the trigonal prisms. Owing to this insertion, the Mn atoms exhibit, in the three phases, an "exotic" oxidation state of about +4.5. In addition, even if the sequence between face sharing MnO6 octahedra and NaO6 trigonal prisms can be analytically deduced from the x value, it is clear that the Na/Mn contrasts play in favour of its accurate determination through the XRD single crystal refinement.
Title:
Spin and Charge Order in the Doped Hubbard Model: Long-Wavelength Collective Modes
Authors:
Chang, CC; Zhang, SW Author Full Names: Chang, Chia-Chen; Zhang, Shiwei
Source:
PHYSICAL REVIEW LETTERS 104 (11): Art. No. 116402 MAR 19 2010
Abstract:
Determining the properties of the two-dimensional Hubbard model is an outstanding problem in physics. Applying recent advances in constrained path auxiliary-field quantum Monte Carlo techniques and simulating large rectangular supercells, we characterize the magnetic and charge properties in the ground state as a function of doping. At intermediate interaction strengths, an incommensurate spin density wave (SDW) state is found, with antiferromagnetic order and essentially homogeneous charge correlation. The wavelength of the collective mode decreases with doping, as does its magnitude. The SDW order vanishes beyond a critical doping. As the interaction is increased, the holes go from a wavelike (delocalized) to a particlelike (localized) state, and charge ordering develops which eventually evolves into stripelike states.
Title:
Quantum dislocations: the fate of multiple vacancies in two-dimensional solid He-4
Authors:
Rossi, M; Vitali, E; Galli, DE; Reatto, L Author Full Names: Rossi, M.; Vitali, E.; Galli, D. E.; Reatto, L.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (14): Art. No. 145401 APR 14 2010
Abstract:
Defects are believed to play a fundamental role in the supersolid state of He-4. We have studied solid He-4 in two dimensions (2D) as a function of the number of vacancies n(v), up to 30, inserted in the initial configuration at rho = 0.0765 angstrom(-2), close to the melting density, with the exact zero-temperature shadow path integral ground state method. The crystalline order is found to be stable also in the presence of many vacancies and we observe two completely different regimes. For small n(v), up to about 6, vacancies form a bound state and cause a decrease of the crystalline order. At larger n(v), the formation energy of an extra vacancy at fixed density decreases by one order of magnitude to about 0.6 K. It is no longer possible to recognize vacancies in the equilibrated state because they mainly transform into quantum dislocations and crystalline order is found almost independently of how many vacancies have been inserted in the initial configuration. The one-body density matrix in this latter regime shows a non-decaying large distance tail: dislocations, that in 2D are point defects, turn out to be mobile, their number is fluctuating, and they are able to induce exchanges of particles across the system mainly triggered by the dislocation cores. These results indicate that the notion of the incommensurate versus the commensurate state loses meaning for solid He-4 in 2D, because the number of lattice sites becomes ill defined when the system is not commensurate. Crystalline order is found to be stable also in 3D in the presence of up to 100 vacancies.
Title:
Characterization of microstructures obtained in wedge shaped Al-Zn-Mg ingots
Authors:
Suarez, MA; Alvarez, O; Alvarez, MA; Rodriguez, RA; Valdez, S; Juarez, JA Author Full Names: Suarez, M. A.; Alvarez, O.; Alvarez, M. A.; Rodriguez, R. A.; Valdez, S.; Juarez, J. A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 492 (1-2): 373-377 MAR 4 2010
Abstract:
The structure present in chill casting taper section of A1-5.3at.%Zn + Mg additions between 3 and 40at.%Mg have been studied by scanning electron microscopy, microanalysis and X-ray diffractometry in order to relate the impact of intermetallic phases such as the tau-Mg-32(Al,Zn)(49) obtained at low Mg-contents with an approximant phase related to quasicrystals at high Mg-contents on its electrochemical efficiency. After microstructural and electrochemical efficiency characterization, it was found that an alloy composition of A1-5.3at.%Zn-10at.%Mg showed a microstructure which consisted of alpha-Al dendrites with tau-phase precipitates showing an electrochemical efficiency of 90% fulfilling the needs for cathodic protection application of structural steels in sea water. (C) 2009 Elsevier B.V. All rights reserved.

Update: 1-Apr-2010

Title:
Transverse modulation and uniform period in Bi1-xSrxMnO3
Authors:
Nagao, M; Kimoto, K; Matsui, Y Author Full Names: Nagao, M.; Kimoto, K.; Matsui, Y.
Source:
PHYSICA B-CONDENSED MATTER 405 (7): 1686-1689 APR 1 2010
Abstract:
The crystal structures of the superstructure phases of the Bi-based manganite Bi1-xSrxMnO3 have been studied by transmission electron microscopy. On the basis of the selected area electron diffraction patterns, our crystallographic analysis revealed that the modulations of Bi1-xSrxMnO3 consist of only transverse modulation associated with the Pcnn-type symmetry, in contrast to the previously believed Ibmm-type symmetry. Moreover, our high-resolution transmission electron microscopy image indicated that a modulation with a noninteger-multiple period has a uniform period but not the mixed state of adjacent integer-multiple periods according to the lever rule. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Superspace description of the homologous series Ga2O3(ZnO)(m)
Authors:
Michiue, Y; Kimizuka, N Author Full Names: Michiue, Yuichi; Kimizuka, Noboru
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 117-129 Part 2 APR 2010
Abstract:
A unified description for the structures of the homologous series Ga2O3(ZnO)(m), gallium zinc oxide, is presented using the superspace formalism. The structures were treated as a compositely modulated structure consisting of two subsystems. One is constructed with metal ions and the other with O ions. The ideal model is given, in which the displacive modulations of ions are well described by the zigzag function with large amplitudes. Alternative settings are also proposed which are analogous to the so-called modular structures. The validity of the model has been confirmed by refinements for phases with m = 6 and m = 9 in the homologous series. A few complex phenomena in real structures are taken into account by modifying the ideal model.
Title:
Modulation functions of incommensurately modulated Cr2P2O7 studied by the maximum entropy method (MEM)
Authors:
Li, L; Schonleber, A; van Smaalen, S Author Full Names: Li, Liang; Schoenleber, Andreas; van Smaalen, Sander
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 130-140 Part 2 APR 2010
Abstract:
The maximum entropy method (MEM) has been used to determine electron density in superspace of incommensurately modulated chromium pyrophosphate from X-ray diffraction data measured by Palatinus et al. [(2006), Acta Cryst. B62, 556-566]. Chromium pyrophosphate, Cr2P2O7, contains ordered regions (83% of the volume) and regions with disorder. Analysis of the MEM density has allowed the determination of the displacive modulation functions within ordered regions. The disordered regions can be described as the alternate occupation of two conformations of the pyrophosphate group and two positions of the chromium atom, with occupational probabilities that depend continuously on the phase of modulation t. A structure model based on the interpretation of the MEM density provides a fit to the diffraction data of the same quality as the model given by Palatinus et al. (2006). The failure to find a model that better fits the data is attributed to the intrinsic inaccuracy of similar to 0.01 angstrom for positions derived from the MEM and to the difficulties in constructing an appropriate model for the anharmonic ADPs and their modulation functions from electron densities.

Update: 25-Mar-2010

Title:
Roles of Bond Alternation in Magnetic Phase Diagram of RMnO3
Authors:
Furukawa, N; Mochizuki, M Author Full Names: Furukawa, Nobuo; Mochizuki, Masahito
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (3): Art. No. 033708 MAR 2010
Abstract:
In order to investigate the nature of the antiferromagnetic structures in perovskite RMnO3, we study a Heisenberg J(1)-J(2) model with bond alternation using analytical and numerical approaches. The magnetic phase diagram which includes incommensurate spiral states and commensurate collinear states is reproduced. We discuss that the magnetic structure with spin up arrow up arrow down arrow down arrow configuration (E-type structure) and the ferroelectricity emerge cooperatively to stabilize this phase. Magnetoelastic couplings are crucial to understand the magnetic and electric phase diagram of RMnO3.
Title:
Theory of Unusual Superconducting Phase Transitions in Heavy Fermion Metals at High Magnetic Fields
Authors:
Zhuravlev, V; Maniv, T; Wosnitza, J Author Full Names: Zhuravlev, V.; Maniv, T.; Wosnitza, J.
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS 159 (1-2): 138-142 APR 2010
Abstract:
We present a non-perturbative theory of paramagnetically-driven superconducting (SC) phase transitions in heavy-fermion metals, which reliably determines their stable SC phases, treats properly the corresponding finite jumps of the order parameter, and can account for unusual features reported recently for this type of materials. It is found that for quasi-2D heavy-fermion metals, such as CeCoIn5, at high magnetic fields oriented perpendicular to the highly conducting planes, the effect of the Fulde-Ferrel (FF) modulation is too weak to prevent a direct first-order phase transition from the normal to the uniform SC state. For 3D heavy-fermion metals, such as URu2Si2, the FF modulation stabilizes, under a decreasing magnetic field, a non-uniform SC state via a second-order phase transition from the normal state. However, at a slightly lower field the modulated phase becomes unstable, transforming to a uniform SC state via a first-order transition.
Title:
Simulation of modulated reflections
Authors:
Lovelace, JJ; Winn, MD; Borgstahl, GEO Author Full Names: Lovelace, Jeffrey J.; Winn, Martyn D.; Borgstahl, Gloria E. O.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 285-292 Part 2 APR 2010
Abstract:
In a modulated crystal, the repeating unit is not periodic but contains a disorder of the molecules that can sometimes be described with a mathematical function. In the diffraction pattern from such a modulated crystal the standard periodic main reflections are flanked by satellite reflections. Generally, incommensurately modulated crystal diffraction cannot be simply described using integers along the reciprocal-lattice directions. However, in the special commensurate case where the satellite spacing is rational relative to the main reflections, a supercell can be used to describe the modulation. Using a supercell allows structural processing to proceed in a 'normal' fashion but with the downside of dealing with many more atoms. Not much is known about the relationship between a highly modulated macromolecular crystal and the resulting satellite intensities so in this study a modulated protein crystal was simulated using a supercell approach. The protein superstructure was modulated to varying degrees and the resultant diffraction patterns and electron-density maps were studied to understand better how a modulation may manifest itself in real protein data. In the case that was evaluated, relatively small structural modulation resulted in significant satellite intensities. Interesting cases were observed where extinguished main reflections had strong satellites.
Title:
The 5:7 Member of the Spin-Ladder Series in the Bi-Sr-Ca-Cu-O System
Authors:
Zaremba, O; Shcherban, O; Akselrud, L; Gladyshevskii, R; Banfi, F; Giannini, E Author Full Names: Zaremba, O.; Shcherban, O.; Akselrud, L.; Gladyshevskii, R.; Banfi, F.; Giannini, E.
Source:
ACTA PHYSICA POLONICA A 117 (1): 42-47 JAN 2010
Abstract:
The crystal structure of the (Bi0.02Sr0.39Ca0.59)(10)Cu17O29 spin-ladder compound was determined from single-crystal X-ray diffraction data. The precursor powder was prepared from stoichiometric amounts of SrCO3, CaCO3, CuO, and Bi2O3 by calcination at 820 degrees C for 20 h and pressed to form a rod used for the crystal growth. The travelling-solvent-floating-zone method was applied in an image furnace to grow large single crystals. The composite commensurate structure was solved and refined in space group F222, Pearson symbol oF224, a = 11.340(2), b = 12.829(2), c = 19.441(3) angstrom, Z = 4. The composite incommensurate structure of the (Bi0.02Sr0.39Ca0.59)(10)Cu17O29 compound was solved and refined in the (3 + 1)-space group F222(00 gamma), a = 11.340(2), b = 12.829(2), c(1) = 2.7773(4), c(2) = 3.8882(6) angstrom, q = 0.7143.

Update: 18-Mar-2010

Title:
Incommensurate 6M-modulated structure of Ni-Fe-Ga martensite
Authors:
Righi, L; Lazpita, P; Gutierrez, J; Barandiaran, JM; Chernenko, VA; Calestani, G Author Full Names: Righi, L.; Lazpita, P.; Gutierrez, J.; Barandiaran, J. M.; Chernenko, V. A.; Calestani, G.
Source:
SCRIPTA MATERIALIA 62 (6): 383-386 MAR 2010
Abstract:
The crystal structure of the modulated, low-temperature matensitic phase in Ni-2 41Fe0 59Ga ferromagnetic shape memory alloy (FSMA) has been determined by Rietveld refinement of neutron powder diffraction data The structure Shows an incommensurate modulated crystal lattice with some analogies with the 7 M modulated martensitic structure Found in Ni2Mn1 2Ga0 8 Heusler alloy The observed type of lattice modulation with q = 0 3521c* gives rise to a new type of martensitic crystal structure in the FSMAs (C) 2009 Acta Materialia Inc Published by Elsevier Ltd All rights reserved
Title:
NMR study of the high-field magnetic phase of LiCuVO4
Authors:
Buttgen, N; Kraetschmer, W; Svistov, LE; Prozorova, LA; Prokofiev, A Author Full Names: Buettgen, N.; Kraetschmer, W.; Svistov, L. E.; Prozorova, L. A.; Prokofiev, A.
Source:
PHYSICAL REVIEW B 81 (5): Art. No. 052403 FEB 2010
Abstract:
We report on NMR studies of the quasi-one-dimensional antiferromagnetic S= 1/2 chain cuprate LiCuVO4, focusing on the high-field spin-modulated phase observed recently in applied magnetic fields H > H-c2(mu H-0(c2) approximate to 7.5 T). The NMR spectra of Li-7 and V-51 around the transition from the ordered to the paramagnetic state were measured. It is shown that the spin-modulated magnetic structure forms with ferromagnetic interactions between spins of neighboring chains within the ab plane at low temperatures 0.6 K < T < T-N. The best fit provides evidence that the mutual orientation between spins of neighboring ab planes is random. For higher temperatures T-N < T less than or similar to 15 K, short-range magnetic order occurs at least on the characteristic time scale of the NMR experiment.
Title:
Revealing the atomic surface structure of the (100) Y-Al-Ni-Co approximant by low-energy electron diffraction and scanning tunneling microscopy
Authors:
Mader, R; Widmer, R; Bauer, B; Gille, P; Groning, P; Steurer, W; Groning, O Author Full Names: Maeder, R.; Widmer, R.; Bauer, B.; Gille, P.; Groening, P.; Steurer, W.; Groening, O.
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064201 FEB 2010
Abstract:
In this paper we present an investigation of the (100) Y-Al75.8Ni2.1Co22.1 surface, which is structurally and chemically related to the (10000) twofold symmetric surface of the decagonal Al-Ni-Co quasicrystal. The atomic surface structure was probed by low-energy electron diffraction (LEED) and by scanning tunneling microscopy (STM), revealing three different surface terminations and three different types of surface reconstructions. All three terminations were successfully assigned to the densest bulk layers and the origin of the surface reconstructions revealed by LEED could be identified locally by STM. The (100) Y-Al-Ni-Co surface shares with the related (10000) d-AlNiCo quasicrystal surface the strong tendency of reconstruction, which in the former case is occurring along the b axis and in the later along the periodic [00001] direction. Gaining a theoretical understanding of the reconstructions of the (100)Y-Al-Ni-Co surface might therefore help to understand the stability of bulk and surface atomic structures in decagonal quasicrystals. Furthermore, due to the strong relation to the quasicrystalline (10000) d-AlNiCo surface, the crystalline (100) Y-Al75.8Ni2.1Co22.1 surface is now a very promising candidate to study directional anisotropies in epitaxial thin film growth, friction, or the electronic structure, with the advantage of representing a much simpler structure (32 atoms/unit cell) which can be theoretically addressed with less effort compared to its quasicrystalline counter part.
Title:
Hydrodynamic structure factor of quasicrystals
Authors:
Chatzopoulos, A; Trebin, HR Author Full Names: Chatzopoulos, Andreas; Trebin, Hans-Rainer
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064205 FEB 2010
Abstract:
A theory of the hydrodynamic structure factor for quasicrystals is developed and exploited. Based on the hydrodynamic equations for icosahedral quasicrystals we introduce the terms of dynamic correlation and response. The phononic and phasonic diffuse part of the dynamic structure factor are examined in detail in frequency and time domain. We present a complete set of solutions for the hydrodynamic equations. Out of the diffusive modes we separately study the phasonic diffusion, the anisotropy of the phasonic diffusion constants, and the general solution for phason wall diffusion. All results include phonon-phason coupling.
Title:
Phason dynamics in one-dimensional lattices
Authors:
Lipp, H; Engel, M; Sonntag, S; Trebin, HR Author Full Names: Lipp, Hansjoerg; Engel, Michael; Sonntag, Steffen; Trebin, Hans-Rainer
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064302 FEB 2010
Abstract:
In quasicrystals, the phason degree of freedom and the inherent anharmonic potentials lead to complex dynamics, which cannot be described by the usual phonon modes of motion. We have constructed simple one-dimensional model systems, the dynamic Fibonacci chain, and approximants thereof. They allow us to study the dynamics of periodic and quasiperiodic structures with anharmonic double-well interactions both by analytical calculations and by molecular-dynamics simulations. We found soliton modes such as breathers and kink solitons and we were able to obtain closed analytical solutions for special cases, which are in good agreement with our simulations. Calculation of the specific heat shows an increase above the Dulong-Petit value, which is due to the anharmonicity of the potential and not caused by the phason degree of freedom.
Title:
Magnetic phase stability of monolayers: Fe on a TaxW1-x(001) random alloy as a case study
Authors:
Ondracek, M; Bengone, O; Kudrnovsky, J; Drchal, V; Maca, F; Turek, I Author Full Names: Ondracek, M.; Bengone, O.; Kudrnovsky, J.; Drchal, V.; Maca, F.; Turek, I.
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064410 FEB 2010
Abstract:
We present an approach to study the magnetic phase stability of magnetic overlayers on nonmagnetic substrates. The exchange integrals among magnetic atoms in the overlayer are estimated in the framework of the adiabatic approximation and used to construct the effective classical two-dimensional Heisenberg Hamiltonian. Its stability is then studied with respect to a large number of collinear and noncollinear magnetic arrangements which include, as special cases, not only ferromagnetic and various antiferromagnetic configurations but also possible incommensurate spin-spiral structures. This allows us to investigate a broader class of systems than a conventional total energy search based on few, subjectively chosen configurations. As a case study we consider the Fe monolayer on the random nonmagnetic bcc-TaxW1-x(001) surface which was studied recently by a conventional approach. We have found a crossover of the ground state of the Fe monolayer from the ferromagnet on the Ta surface to the c(2 x 2) antiferromagnet on the W surface and that at the composition with about 20% of Ta an incommensurate magnetic configuration might exist.
Title:
Stable and variable features of the magnetic structure of fcc Fe/Cu(001) films
Authors:
Sandratskii, LM Author Full Names: Sandratskii, L. M.
Source:
PHYSICAL REVIEW B 81 (6): Art. No. 064417 FEB 2010
Abstract:
After more than a decade of experimental and theoretical studies of the magnetic structure of the fcc Fe/Cu(001) films, most of the researchers agree that the atomic spins of two surface layers are ferromagnetically ordered whereas the magnetic structure of further layers is not ferromagnetic. The conclusions on the magnetic configuration of the nonferromagnetic part vary broadly from a simple collinear layer-by-layer antiferromagnet to complex incommensurate spin-density wave. We report detailed theoretical study of the fcc Fe/Cu(001) films with 6, 7, and 8 ML coverages. The study is based on the density-functional-theory calculations with the code allowing for the consideration of arbitrary noncollinear magnetic configurations. We suggest a view on the magnetism of the Fe/Cu(001) films that includes the grouping of the layers into blocks with robust collinear magnetic structure whereas the variation in the relative directions of the moments of different blocks is energetically relatively inexpensive. The robust magnetic structure of the three surface layers was found to be double down arrow double up arrow double up arrow. Further layers form the pairs with robust antiferromagnetic structure. We demonstrate that the formation of the robust magnetic blocks corresponds to a certain hierarchy of the interlayer exchange interactions. We suggest that the individual defect pattern of each fabricated film influences before all the relative orientation of the block magnetizations keeping the intrablock structure intact. The calculated inter-atomic exchange parameters are used to study magnetic thermodynamics of the films within mean-field approximation. In particular we focus on possible physical reasons of the appearance of the steplike features in the temperature dependence of the magnetization detected experimentally. We emphasize the important consequences of the inequivalence of the Fe atoms belonging to different layers of the film. This inequivalence makes the properties of the films to be essentially different from the properties of the corresponding bulk system. Using a rigid-band model we investigate the dependence of the exchange parameters on the electron number. We critically discuss the possibility of the formation of the incommensurate SDW in the thin Fe/Cu(001) films. The brief formulation of the idea of robust blocking and its experimental confirmation was recently published as a letter [H. L. Meyerheim, J.-M. Tonnerre, L. M. Sandratskii et al., Phys. Rev. Lett. 103, 267202 (2009)].
Title:
Electronic structure, magnetic, and dielectric properties of the edge-sharing copper oxide chain compound NaCu2O2
Authors:
Leininger, P; Rahlenbeck, M; Raichle, M; Bohnenbuck, B; Maljuk, A; Lin, CT; Keimer, B; Weschke, E; Schierle, E; Seki, S; Tokura, Y; Freeland, JW Author Full Names: Leininger, Ph.; Rahlenbeck, M.; Raichle, M.; Bohnenbuck, B.; Maljuk, A.; Lin, C. T.; Keimer, B.; Weschke, E.; Schierle, E.; Seki, S.; Tokura, Y.; Freeland, J. W.
Source:
PHYSICAL REVIEW B 81 (8): Art. No. 085111 FEB 2010
Abstract:
We report an experimental study of NaCu2O2, a Mott insulator containing chains of edge-sharing CuO4 plaquettes, by polarized x-ray absorption spectroscopy (XAS), resonant magnetic x-ray scattering (RMXS), magnetic susceptibility, and pyroelectric current measurements. The XAS data show that the valence holes reside exclusively on the Cu2+ sites within the copper-oxide spin chains and populate a d orbital polarized within the CuO4 plaquettes. The RMXS measurements confirm the presence of incommensurate magnetic order below a NEel temperature of T-N = 11.5 K, which was previously inferred from neutron powder-diffraction and nuclear-magnetic-resonance data. In conjunction with the magnetic-susceptibility and XAS data, they also demonstrate an "orbital" selection rule for RMXS that is of general relevance for magnetic-structure determinations by this technique. Dielectric property measurements reveal the absence of significant ferroelectric polarization below TN, which is in striking contrast to corresponding observations on the isostructural compound LiCu2O2. The results are discussed in the context of current theories of multiferroicity.
Title:
Ordered oxide layers on the pentagonal surface of AlPdMn quasicrystal
Authors:
Burkardt, S; Erbudak, M Author Full Names: Burkardt, S.; Erbudak, M.
Source:
PHYSICAL REVIEW B 81 (8): Art. No. 085417 FEB 2010
Abstract:
Recently, we reported the structural investigation of the oxide layers grown on the pentagonal surface of icosahedral Al70Pd20Mn10 quasicrystal based on low-energy electron diffraction. The oxide layer was described to consist of five twin domains rotated by 2 pi/5 with respect to each other in accordance with the symmetry of the quasicrystalline substrate each of which having one twofold-symmetry direction of the substrate as a mirror plane. Here, we discuss the oxidation process in more detail and report the growth of different oxide structures depending on the sample temperature and its pretreatment. At room temperature, amorphous oxide layers form. In contrast five distinct and few-nanometer-large domains possessing an internal hexagonal structure with substantial amount of contribution from antiphase domain boundaries grow at 700-800 K for small and large coverage. In an intermediate range, a mixture of antiphase domain-boundary contributions and fractional-order spots characteristic to a 2 root 3(1x1)R +/- 30 degrees S reconstruction of the surface oxide layer is found which additionally stabilized the interface. The previously reported twin-domain model, which was derived after an ion bombardment of the preoxidized surface with subsequent reoxidation, is identified as an oxide layer grown on the (110) surface of a crystalline Al-50(PdMn)(50) alloy as a result of the sputtering.
Title:
THE THERMAL CONDUCTIVITY OF Al73Mn27-xFex TAYLOR PHASES
Authors:
Stanic, D; Popcevic, P; Smiljanic, I; Bihar, Z; Lukatela, J; Leontic, B; Bilusic, A; Batistic, I; Smontara, A Author Full Names: Stanic, Denis; Popcevic, Petar; Smiljanic, Igor; Bihar, Zeljko; Lukatela, Jagoda; Leontic, Boran; Bilusic, Ante; Batistic, Ivo; Smontara, Ana
Source:
MATERIALI IN TEHNOLOGIJE 44 (1): 3-7 JAN-FEB 2010
Abstract:
The thermal conductivity (kappa) of Al73Mn27-xFex (x = 0, 2, 4, 6) complex metallic alloys has been measured in the temperature interval from 2 K to 300 K. All the alloys are Taylor (T) phases, except Al73Mn21Fe6, which is a decagonal (d) quasicrystal. The behaviours of kappa are typical for complex metallic alloys, i.e.. a relatively small magnitude, a Change of slope about 50 K and an increase of the conductivity above 100 K. At room temperature the magnitude of kappa for all the samples is between 2.7 W/mK and 3.3 W/mK. which is comparable to that of thermally insulating amorphous SiO2 and Zr/YO2 ceramics. The reason for such a low thermal conductivity is because both, the electronic and lattice conductivity are low. The electronic contribution to the thermal conductivity is low because of the large electrical resistivity of the samples. The lattice (hernial conductivity is greatly reduced because of the enhanced umklapp process of the phonon scattering (caused by (lie large lattice constant) and by the disorder in the structure.
Title:
HALL EFFECT IN THE CRYSTALLINE ORTHOROMBIC o-Al13Co4 APPROXIMANT TO THE DECAGONAL QUASICRYSTALS
Authors:
Ivkov, J; Stanic, D; Popcevic, P; Smontara, A; Dolinsek, J; Gille, P Author Full Names: Ivkov, Jovica; Stanic, Denis; Popcevic, Petar; Smontara, Ana; Dolinsek, Janez; Gille, Peter
Source:
MATERIALI IN TEHNOLOGIJE 44 (1): 9-12 JAN-FEB 2010
Abstract:
We have investigated the anisotropic Hall effect of the o-Al13Co4 orthorhombic approximant to the decagonal phase. The crystalline-direction-dependent measurements were Performed along the a, b and c direction of the orthorhombic Unit cell. The Hall all effect has been measured for all the combinations of the electrical current and magnetic field directions. The Hall coefficients RI, change with the crystallographic direction from negative electron-like or zero to positive hole-like for different combinations of the current and field directions. The results for the anisotropy of R-n is well correlated with the anisotropy of Rn in the d-Al-Ni-Co and d-Al-Cu-Co quasicrystals. The Hall coefficients of the o-Al13Co4 phase were compared to the literature data on single crystals of the Al76Co22Ni2 and the Al80Cr15Fe5 approximants to the decagonal quasicrystals. allowing I study of the evolution of the Hall coefficient with an increasing structural complexity and unit-cell size.

Update: 4-Mar-2010

Title:
STRUCTURE AND PROPERTIES FEATURES OF Ti-Zr-Ni-QUASICRYSTALS
Authors:
Azhazha, VM; Malykhin, SV; Merisov, BA; Pugachov, AT; Khadzhay, GY Author Full Names: Azhazha, V. M.; Malykhin, S. V.; Merisov, B. A.; Pugachov, A. T.; Khadzhay, G. Ya.
Source:
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY (6): 115-126 2009
Abstract:
For Ti-Zr-Ni ingots prepared by equilibrium crystallization, and 20 to 100 gm ribbons obtained by rapid quenching on the same disc, the dependence of phase composition on the super-pure components charge mixture composition and on the disc velocity has been studied. The technology parameters for synthesis of QC single-phase structures or ones with prevailing portion of icosahedral quasicrystalline structure were determined. The peculiarities of structure,. substructure and stress state of the ribbons were studied. Through the ribbon section, the gradient variations of phase composition, grain size, micro- and nano-hardness, Young modulus, structure and substructure parameters, and residual stress level were established. The gradient distributions depend on the quenching speed. The temperature behaviour of electrical resistivity without external magnetic field and under magnetic field was investigated. The transition to superconductivity state was found. The properties of! hydrogen accumulation and the parameters of its diffusion, as well as mechanical properties and deformation features, and thermo-physical properties of Ti-Zr-Ni quasicrystals were studied. The evolution of structure and stress state in quasicrystals as a result of thermal influence, hydrogen saturation, and irradiation was analyzed.
Title:
Origin of Friction Anisotropy on a Quasicrystal Surface
Authors:
Filippov, AE; Vanossi, A; Urbakh, M Author Full Names: Filippov, Aleksander E.; Vanossi, Andrea; Urbakh, Michael
Source:
PHYSICAL REVIEW LETTERS 104 (7): Art. No. 074302 FEB 19 2010
Abstract:
Wearless friction force experiments [Science 309, 1354 (2005)] have recently demonstrated that tribological response in quasicrystals could be related to the exotic atomic structure of the bulk material. Here, by numerical simulations, we address the origin of the experimentally observed friction anisotropy on a twofold decagonal quasicrystal surface. We predict the distinct stick-slip patterns in the lateral force along the periodic and quasiperiodic directions, specifically exploring the temperature dependence that rules the transitions between single and multiple-slip regimes of motion.
Title:
Geometrical property of the cluster model of the Yb-Cd icosahedral quasicrystal (vol 88, pg 1905, 2008)
Authors:
Takakura, H Author Full Names: Takakura, H.
Source:
PHILOSOPHICAL MAGAZINE 90 (5): 525-525 2010
Title:
The magnetic structure of clinopyroxene-type LiFeGe2O6 and revised data on multiferroic LiFeSi2O6
Authors:
Redhammer, GJ; Roth, G; Treutmann, W; Hoelzel, M; Paulus, W; Andre, G; Pietzonka, C; Amthauer, G Author Full Names: Redhammer, Guether J.; Roth, Georg; Treutmann, Werner; Hoelzel, Markus; Paulus, Werner; Andre, Gilles; Pietzonka, Clemens; Amthauer, Georg
Source:
JOURNAL OF SOLID STATE CHEMISTRY 182 (9): 2374-2384 SEP 2009
Abstract:
The clinopyroxene compounds LiFeSi2O6 and LiFeGe2O6 have been investigated by constant wavelength neutron diffraction at low temperatures and by bulk magnetic measurements. Both compounds are monoclinic, space group P2(1)/c and do not exhibit a change in nuclear symmetry down to 1.4 and 5 K respective. However, they transform to a magnetically ordered state below 20 K. LiFeSi2O6 shows a simple magnetic structure with no indication of an incommensurate modulation. The magnetic space group is P2(1)/c' and the structure is described by a ferromagnetic coupling of spins within the infinite M1 chains of edge-sharing octahedra, while the coupling between these M1 chains is antiferromagnetic. The magnetic phase transition is accompanied by magnetostriction of the lattice when passing through the magnetic phase transition. The magnetic structure of LiFeGe2O6 is different to the silicate: the space group is P2(1)'/c and the magnetic unit cell doubled along the a-direction. Within the M1 chains spins are coupled antiferromagnetically, while the chain to chain coupling is antiferromagnetic when coupling goes via the GeB tetrahedron and ferromagnetic when it goes via the GeA tetrahedron. (C) 2009 Elsevier Inc. All rights reserved.
Title:
Magnetic and structural properties of the magnetic shape memory compound Ni2Mn1.48Sb0.52
Authors:
Brown, PJ; Gandy, AP; Ishida, K; Ito, W; Kainuma, R; Kanomata, T; Neumann, KU; Oikawa, K; Ouladdiaf, B; Sheikh, A; Ziebeck, KRA Author Full Names: Brown, P. J.; Gandy, A. P.; Ishida, K.; Ito, W.; Kainuma, R.; Kanomata, T.; Neumann, K. U.; Oikawa, K.; Ouladdiaf, B.; Sheikh, A.; Ziebeck, K. R. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (9): Art. No. 096002 MAR 10 2010
Abstract:
Magnetization and high resolution neutron powder diffraction measurements on the magnetic shape memory compound Ni2Mn1.48Sb0.52 have confirmed that it is ferromagnetic below 350 K and undergoes a structural phase transition at T-M approximate to 310 K. The high temperature phase has the cubic L2(1) structure with a = 5.958 angstrom, with the excess manganese atoms occupying the 4(b) Sb sites. In the cubic phase above approximate to 310 K the manganese moments are ferromagnetically aligned. The magnetic moment at the 4(a) site is 1.57(12) mu(B) and it is almost zero (0.15(9) mu(B)) at the 4(b) site. The low temperature orthorhombic phase which is only fully established below 50 K has the space group Pmma with a cell related to the cubic one by a Bain transformation a(orth) = (a(cub) + b(cub))/2; b(orth) = c(cub) and c(orth) = (a(cub) - b(cub)). The change in cell volume is approximate to 2.5%. The spontaneous magnetization of samples cooled in fields less than 0.5 T decreases at temperatures below T-M and at 2 K the magnetic moment per formula unit in fields up to 5.5 T is 2.01(5) mu(B). Neutron diffraction patterns obtained below approximate to 132 K gave evidence for a weak incommensurate magnetic modulation with propagation vector (2/3, 1/3, 0).
Title:
Structures and Phase Transitions in (MoO2)(2)P2O7
Authors:
Lister, SE; Soleilhavoup, A; Withers, RL; Hodgkinson, P; Evans, JSO Author Full Names: Lister, Sarah E.; Soleilhavoup, Anne; Withers, Ray L.; Hodgkinson, Paul; Evans, John S. O.
Source:
INORGANIC CHEMISTRY 49 (5): 2290-2301 MAR 1 2010
Abstract:
We report structural investigations into (MoO2)(2)P2O7 using a combination of X-ray, neutron and electron diffraction, and solid-state NMR supported by first principles quantum chemical calculations. These reveal a series of phase transitions on cooling at temperatures of 377 and 325 K. The high temperature gamma-phase has connectivity consistent with that proposed by Kierkegaard at room temperature (but with improved bond length distribution), and contains 13 unique atoms in space group Pnma with lattice parameters a = 12.6577(1) angstrom, b = 6.3095(1) angstrom, c = 10.4161 (1) angstrom, and volume 831.87(1) angstrom(3) from synchrotron data at 423 K. The low temperature alpha-structure was indexed from electron diffraction data and contains 60 unique atoms in space group P2(1)/c with cell parameters a = 17.8161(3) angstrom, b = 10.3672(1) angstrom, c = 17.8089(3) angstrom, beta = 90.2009(2)degrees, and volume 3289.34(7) angstrom(3) at 250 K. First principles calculations of P-31 chemical shift and J couplings were used to establish correlation between local structure and observed NMR parameters, and 1D and 2D P-31 solid-state NMR used to validate the proposed crystal structures. The intermediate beta-phase is believed to adopt an incommensurately modulated structure; P-31 NMR suggests a smooth structural evolution in this region.

Update: 25-Feb-2010

Title:
Modulated Lanthanum Chains in the Crystal Structure of La-3.65[Ru(C-2)(3)]
Authors:
Davaasuren, B; Dashjav, E; Doert, T; Kreiner, G; Schnelle, W; Wagner, FR; Mihalkovic, M; Kniep, R Author Full Names: Davaasuren, Bambar; Dashjav, Enkhtsetseg; Doert, Thomas; Kreiner, Guido; Schnelle, Walter; Wagner, Frank R.; Mihalkovic, Marek; Kniep, Ruediger
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE 636 (1): 41-49 2010
Abstract:
Lanthanum ruthenium carbide La-3.65[Ru(C-2)(3)] crystallizes hexagonal (P6(3)/m with a 887.9(2) pm and c = 1606.8(6) pm, V = 1096.8(4).10(6) nm(3), and Z = 6. The crystal structure contains trigonal-planar Ru(C-2)(3) groups and lanthanum atoms, which form a partial structure of the chemical composition La3Ru(C-2)(3). Additional lanthanum atoms Occupy hexagonal channels built by those carbon atoms of the C-2 ligands, which are non-bonded to the central ruthenium atoms. The distribution of these lanthanum atoms along the c axis results ill a threefold superstructure, which was refined as a commensurate modulated structure (P6(3)/m (00g)s0, q = (0, 0, 1/3)). Harmonic occupational and displacive modulation functions Were used for the structure refinement. The structure converged to R-1 = 4.9 % for all data (R-1 = 2.6 % for the main reflections, R-1 = 11.1 % for the 1(st) order satellite reflections). A small homogeneity range for this phase is predicted by total energy calculations using the PAW-GGA method (VASP). Chemical bonding analysis reveals that file C-2 pairs are best described as acetylide C-2(2-) units.
Title:
SimulaTEM: Multislice simulations for general objects
Authors:
Gomez-Rodriguez, A; Beltran-del-Rio, LM; Herrera-Becerra, R Author Full Names: Gomez-Rodriguez, A.; Beltran-del-Rio, L. M.; Herrera-Becerra, R.
Source:
ULTRAMICROSCOPY 110 (2): 95-104 JAN 2010
Abstract:
In this work we present the program SimulaTEM for the simulation of high resolution micrographs and diffraction patterns. This is a program based on the multislice approach that does not assume a periodic object. It can calculate images from finite objects, from amorphous samples, from crystals, quasicrystals, grain boundaries, nanoparticles or arbitrary objects provided the coordinates of all the atoms can be supplied. (C) 2009 Elsevier B.V. All rights reserved.
Title:
A Tm-169-Mossbauer spectroscopy investigation of orthorhombic phase o-TmMnO3
Authors:
Salama, HA; Stewart, GA; Hutchison, WD; Nishimura, K; Scott, DR; O'Neill, HS Author Full Names: Salama, H. A.; Stewart, G. A.; Hutchison, W. D.; Nishimura, K.; Scott, D. R.; O'Neill, H. StC.
Source:
SOLID STATE COMMUNICATIONS 150 (5-6): 289-291 JAN 2010
Abstract:
AC susceptibility and specific heat measurements confirm that the Mn sub-lattice of o-TmMnO3 orders at T-N(Mn) approximate to 41 K with a weaker feature at T-C approximate to 32 K. Tm-169-Mossbauer spectra are interpreted in terms of a single, asymmetric, quadrupole-split doublet whose line width increases sharply at T-C. This suggests the presence of a weak induced Tm-site moment, consistent with claims that the Mn sub-lattice magnetism undergoes a transition from incommensurate to collinear antiferromagnetic order at this temperature. (C) 2009 Elsevier Ltd. All rights reserved.
Title:
Direction of modulation during twin boundary motion
Authors:
Chulist, R; Oertel, CG; Skrotzki, W; Lippmann, T Author Full Names: Chulist, R.; Oertel, C. -G.; Skrotzki, W.; Lippmann, T.
Source:
SCRIPTA MATERIALIA 62 (5): 235-237 MAR 2010
Abstract:
To study the change of modulation direction during deformation, two NiMnGa single crystals, one with a five-layered modulated tetragonal structure (5 M) and the other with a seven-layered modulated orthorhombic structure (7 M), were chosen. Synchrotron diffraction experiments show that the modulation takes place on the {1 1 0) plane along the < 1 1 0] directions. During deformation the c-axis orientation changes by twinning, and with this the direction of modulation obeying the twin relation also changes. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Geometrical property of the cluster model of the Yb-Cd icosahedral quasicrystal (vol 88, pg 1905, 2008)
Authors:
Takakura, H Author Full Names: Takakura, H.
Source:
PHILOSOPHICAL MAGAZINE 90 (1-4): 525-525 2010
Title:
LiZnNb4O11.5: A novel oxygen deficient compound in the Nb-rich part of the Li2O-ZnO-Nb2O5 system
Authors:
Morozov, VA; Arakcheeva, AV; Konovalova, VV; Pattison, P; Chapuis, G; Lebedev, OI; Fomichev, VV; Van Tendeloo, G Author Full Names: Morozov, Vladimir A.; Arakcheeva, Alla V.; Konovalova, Vera V.; Pattison, Philip; Chapuis, Gervais; Lebedev, Oleg I.; Fomichev, Valery V.; Van Tendeloo, Gustaaf
Source:
JOURNAL OF SOLID STATE CHEMISTRY 183 (2): 408-418 FEB 2010
Abstract:
A novel lithium zinc niobium oxide LiZnNb4O11.5 (LZNO) has been found in the Nb-rich part of Li2O-ZnO-Nb2O5 system. LZNO, with an original alpha-PbO2 related structure, has been synthesized by the routine ceramic technique and characterized by X-ray diffraction and transmission electron microscopy (TEM). Reflections belonging to the LZNO phase, observed in X-ray powder diffraction (XRPD) and electron diffraction, have been indexed as monoclinic with unit cell parameters a=17.8358(9)angstrom, b=15.2924(7)angstrom, c=5.0363(3)angstrom and gamma=96.607(5)degrees or as alpha-PbO2-like with lattice constants a=4.72420(3)angstrom, b=5.72780(3)angstrom, c=5.03320(3)angstrom, gamma=90.048(16)degrees and modulation vector q=0.3a*+1.1b* indicating a commensurately modulated alpha-PbO2 related structure. The monoclinic cell is a supercell related to the latter. Using synchrotron powder diffraction data, the structure has been solved and refined as a commensurate modulation (superspace group P112(1)/n(alpha beta 0)00) as well as a supercell (space group P2(1)/b). The superspace description allows us to consider the LZNO structure as a member of the proposed alpha-PbO2-Z (3 + 1)D structure type, which unifies both incommensurately and commensurately modulated structures. HRTEM reveals several types of defects in LZNO and structural models for these defects are proposed. Two new phases in Li2O-ZnO-Nb2O5 system are predicted on the basis of this detailed HRTEM analysis. (C) 2009 Elsevier Inc. All rights reserved.
Title:
Cooperative effect of monoclinic distortion and sinusoidal modulation in the martensitic structure of Ni2FeGa
Authors:
Lu, JB; Yang, HX; Tian, HF; Zeng, LJ; Ma, C; Feng, L; Wu, GH; Li, JQ; Jansen, J Author Full Names: Lu, J. B.; Yang, H. X.; Tian, H. F.; Zeng, L. J.; Ma, C.; Feng, L.; Wu, G. H.; Li, J. Q.; Jansen, J.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 183 (2): 425-430 FEB 2010
Abstract:
The structural features of the "5M" martensitic phase in Ni2FeGa alloys have been determined by electron diffraction using the multi-slice least-squares (MSLS) method. The results demonstrate that the "5M" phase contains an evident cooperative effect of monoclinic distortion and sinusoidal modulation along the [110](c) direction. Theoretical simulations based on Our refined data suggest that the "5M" martensitic phase observed in Ni-Fe-Ga and Ni-Mn-Ga has visible common behaviors in both stacking sequence and local structural distortion. Considering the cooperative effect of monoclinic distortion and sinusoidal modulation, we demonstrate that the "7M" martensitic phase could adopt two equivalent structural phases corresponding with the stacking sequences of (43). and (52)2, respectively. Crown Copyright (C) 2009 Published by Elsevier Inc. All rights reserved.
Title:
Advantages of aberration correction for HRTEM investigation of complex layer compounds
Authors:
Spiecker, E; Garbrecht, M; Jager, W; Tillmann, K Author Full Names: Spiecker, E.; Garbrecht, M.; Jaeger, W.; Tillmann, K.
Source:
JOURNAL OF MICROSCOPY-OXFORD 237 (3): 341-346 MAR 2010
Abstract:
Aberration-corrected high-resolution transmission electron microscopy (HRTEM) has been applied to resolve the atomic structure of a complex layered crystal, (PbS)(1.14)NbS2, which comprises a high density of incommensurate interfaces. The strong suppression of image delocalization and the favourable contrast transfer under negative C-s imaging (NCSI) conditions have been exploited for obtaining HRTEM images which directly reveal the projected crystal structure and allow to study lattice imperfections, like stacking disorder and layer undulations, with atomic scale resolution. The advantages of aberration-corrected HRTEM over conventional HRTEM are demonstrated by direct comparison of experimental images and computer simulations.
Title:
Microstructure of electrodeposited NiFe/Cu multilayers
Authors:
Tokarz, A; Wieczorek, P; Lis, AK; Morgiel, J Author Full Names: Tokarz, A.; Wieczorek, P.; Lis, A. K.; Morgiel, J.
Source:
JOURNAL OF MICROSCOPY-OXFORD 237 (3): 456-460 MAR 2010
Abstract:
NiFe/Cu multilayer films have been electrodeposited potentiostatically on (001)-oriented Si and polycrystalline Cu substrates by a single bath technique. Standard error of mean and energy dispersive X-ray studies of single NiFe(Cu) layers allow us to establish the right deposition parameters for NiFe and Cu sublayer. Standard error of mean results reveal the layered structure of deposits for relatively thick bilayer thickness (ca. similar to 200 nm). The modulated structure of NiFe/Cu multilayers with extremely thin bilayer thickness (nominal period Lambda = 8 nm) was investigated by transmission electron microscope techniques. A columnar structure of the deposit with column diameter in the range from 10 to 30 nm was observed. These results are comparable with X-ray diffraction measurements of crystallites size obtained by Scherer equation. The line scans acquired using EDS confirmed the layered structure of the deposit, but pointed towards possibility of intermixing! of species from alternating sublayers especially in case of those with finer period.
Title:
Effect of Titanium, Antimony, Cerium and Carbon Nanotubes on the Morphology and Microhardness of Mg-based Icosahedral Quasicrystal Phase
Authors:
Wang, ZF; Zhao, WM; Li, HP; Ding, J; Li, YY; Liang, CY Author Full Names: Wang, Zhifeng; Zhao, Weimin; Li, Haipeng; Ding, Jian; Li, Yongyan; Liang, Chunyong
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY 26 (1): 27-32 JAN 2010
Abstract:
For the first time, petal-like and spherical Mg-based icosahedral quasicrystal phase (I-phase) were obtained by introducing Ti, Sb, Ce and C nanotubes into Mg-Zn-Y alloy under normal casting conditions. The formation mechanism and stability criterion of spherical I-phase were discussed. The morphology and microhardness of I-phase and their determinants were studied in this paper. The results show that the different value of microhardness of I-phase could be attributed to the different kinds of the fourth component and its content, and its different innate characters. The final morphology of icosahedral quasicrystalline (IQC) is decided by the size of critical stable radius R-r, the content of the fourth component and degree of undercooling.
Title:
SUPERCONDUCTIVITY, SPIN AND CHARGE DENSITY STRUCTURES IN ONE AND TWO-DIMENSIONAL SELF-CONSISTENT MODELS
Authors:
Matveenko, SI Author Full Names: Matveenko, S. I.
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B 23 (20-21): 4297-4310 Sp. Iss. SI AUG 20 2009
Abstract:
We review some analytical results of our studies of the charge- and spin density modulations (CDW and SDW) in a one- and two-dimensional electron systems. Self-consistent solutions of Bogoliubov-de Gennes equations for spin-charge solitonic superstructure and superconducting state are obtained in the framework of one and two-dimensional extended Hubbard models. Possible correspondence of the theory with experimental data on stripe phase in high T-c cuprates is discussed. We found various solutions for the two-dimensional self-consistent model of superconductors with d(x2-y2) symmetry of the order parameter, taking into account spin and charge distributions. Analytical solutions for spin-charge density wave phases in the absence of the superconductivity("stripe" and "checkerboard" structures) are presented. Analytical solutions for coexisting superconductivity and stripe-phase modulations in the cores of the Abrikosov's vortices are also found.

Update: 18-Feb-2010

Title:
STUDY OF Al-Cu-Fe-Ti-Cr-Si POWDERS FOR THERMAL SPRAYING PRODUCED BY MECHANOCHEMICAL SYNTHESIS AND SUBSEQUENT ANNEALING
Authors:
Borisova, AL; Adeeva, LI; Tunik, AY; Karpets, MV; Rupchev, VL; Burlachenko, AN Author Full Names: Borisova, A. L.; Adeeva, L. I.; Tunik, A. Yu.; Karpets, M. V.; Rupchev, V. L.; Burlachenko, A. N.
Source:
POWDER METALLURGY AND METAL CERAMICS 48 (9-10): 514-521 SEP 2009
Abstract:
The paper examines the phase transformations of composite powders based on Al63Cu25Fe12 that contain alloying elements (Ti, Cr, Si in the ratio AlCuFe : TiCrSi = 75 : 25). The powders are produced by mechanochemical synthesis and subsequent thermal treatment. Amorphous and crystalline powder mixtures form during synthesis; their annealing results in multiphase structures consisting of alpha, beta(1), and beta(2) phases. High-temperature x-ray diffraction has revealed an alpha-phase between 700 and 900 degrees C. The new a-phase should be regarded as a 1/1 approximant of the nonequilibrium quasicrystalline phase. The maximum content of the approximant phase (68 wt.%) is observed after five-hour synthesis and subsequent annealing (T = 700 degrees C, tau = 2 h) of pressed powders, microhardness of the particles reaching 8900 MPa.
Title:
The surface science of quasicrystals
Authors:
McGrath, R; Smerdon, JA; Sharma, HR; Theis, W; Ledieu, J Author Full Names: McGrath, R.; Smerdon, J. A.; Sharma, H. R.; Theis, W.; Ledieu, J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (8): Art. No. 084022 MAR 3 2010
Abstract:
The surfaces of quasicrystals have been extensively studied since about 1990. In this paper we review work on the structure and morphology of clean surfaces, and their electronic and phonon structure. We also describe progress in adsorption and epitaxy studies. The paper is illustrated throughout with examples from the literature. We offer some reflections on the wider impact of this body of work and anticipate areas for future development.
Title:
Phase field simulation of microstructure evolution in Fe-Cr-Co alloy during thermal magnetic treatment and step aging
Authors:
Lv, LX; Zhen, L; Xu, CY; Sun, XY Author Full Names: Lv, L. X.; Zhen, L.; Xu, C. Y.; Sun, X. Y.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (8): 987-995 APR 2010
Abstract:
The evolution of modulated structures in Fe-Cr-Co alloys during isothermal aging under an external magnetic field and multiple step aging was simulated based on a phase field method. In this simulation, the magnetic configuration during the decomposition was calculated by a micromagnetic method, and the chemical Gibbs energy function was calculated by the CALPHAD approach based on the experimental equilibrium phase diagram. The calculation results provide a quantitative microstructure change directly linked to the phase diagram and demonstrate obvious microstructure difference between isothermal aging and multiple aging. The ferromagnetic precipitates elongate along the direction of the external magnetic field. The simulated evolution and microstructure are in good agreement with the experimental results. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Desorption of hydrogen from Ti-Zr-Ni hydrides using a mass spectrometer
Authors:
Kocjan, A; McGuiness, PJ; Kobe, S Author Full Names: Kocjan, A.; McGuiness, P. J.; Kobe, S.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 35 (1): 259-265 JAN 2010
Abstract:
We have performed thermogravimetry (TG) and mass-spectrometry measurements of hydrogen desorbed from fully and partially hydrided ternary Ti-Zr-Ni amorphous, quasi-crystalline and crystalline alloys, with four different initial compositions, where the Ti/Zr ratio ranged from 1 to 2.4. The icosahedral, quasicrystalline Ti-Zr-Ni samples were obtained using the melt-spinning technique, and with subsequent annealing of these ribbons at 700 degrees C for 2 h in vacuum we were able to obtain a mixture of crystalline C14 Laves and alpha/beta solid-solution phases. in addition, using subsequent mechanical alloying we produced amorphous powders of Ti-Zr-Ni from the as-spun ribbons. These various samples were then hydrided and analyzed by TG and mass spectrometry. The TG measurements provided us with the mass% of desorbed hydrogen, whereas the mass-spectrometry revealed information about the hydrogen desorption temperatures in the material. Despite the fact that the amorphous and icosahedral. samples undergo some crystallization during the desorption measurements, the resulting mass spectra were different and were closely related to the alloy's structure. In contrast, the shapes of mass spectra were less affected by the composition, the total amount of desorbed hydrogen and the loading pressure. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Title:
Crystal Structure and Optical and Magnetic Properties of Pr-2(MoO4)(3)
Authors:
Logvinovich, D; Arakcheeva, A; Pattison, P; Eliseeva, S; Tomes, P; Marozau, I; Chapuis, G Author Full Names: Logvinovich, D.; Arakcheeva, A.; Pattison, P.; Eliseeva, S.; Tomes, P.; Marozau, I.; Chapuis, G.
Source:
INORGANIC CHEMISTRY 49 (4): 1587-1594 FEB 15 2010
Abstract:
Praseodymium molybdate Pr-2(MoO4)(3) was synthesized using the standard ceramic route. The crystal structure of the material has been successfully solved in superspace group /2/b(alpha beta 0)00 with lattice constants a = 5.30284(4), b = 5.32699(3), c= 11.7935(1) angstrom, gamma = 90.163(1)degrees, and the modulation vector q = 2/3a* + 0.88810(2)b*. The deviation of the q vector from a rational value allows a description of the structure in terms of nanosize domains with the La-2(MoO4)(3)-like structure separated by stacking faults. Under 450 nm excitation, (P-3(0) level) Pr-2(MoO4)(3) exhibits the characteristic red emission, with the most intense band at 649 nm corresponding to a P-3(0) -> F-3(2) transition. Magnetic susceptibility measurements reveal Curie-Weiss paramagnetism with predominating antiferromagnetic interactions between PI-magnetic moments and no evidence of magnetic transitions down to T = 5 K.
Title:
Rational Synthesis and Characterization of a New Family of Low Thermal Conductivity Misfit Layer Compounds [(PbSe)(0.99)](m)(WSe2)(n)
Authors:
Lin, QY; Smeller, M; Heideman, CL; Zschack, P; Koyano, M; Anderson, MD; Kykyneshi, R; Keszler, DA; Anderson, IM; Johnson, DC Author Full Names: Lin, Qiyin; Smeller, Mary; Heideman, Colby L.; Zschack, Paul; Koyano, Mikio; Anderson, Michael D.; Kykyneshi, Robert; Keszler, Douglas A.; Anderson, Ian M.; Johnson, David C.
Source:
CHEMISTRY OF MATERIALS 22 (3): 1002-1009 FEB 9 2010
Abstract:
We describe here a general synthesis approach for the preparation of new families of misfit layer compounds and demonstrate its effectiveness through the preparation of the first 64 members of the [(PbSe)(0.99)](m) (WSe2)(n) family of compounds, where in and it are integers that were systematically varied from 1 to 8. The new Compounds [(PbSc)(1+y)](m) (WSe2)(n) were synthesized by annealing reactant precursors containing 177 layers of alternating elemental Pb and Se followed by it layers ofalternating elemental W and Se, in which the thickness of each pair of elemental layers was calibrated to yield a structural bilayer of rock salt structured PbSe and a trilayer of hexagonal WSe2. The compounds are kinetically trapped by the similarity of the composition profiles and modulation lengths in the precursor and the targeted compounds. The structural evolution from initial reactant of layer elements to crystalline misfit layer compounds was tracked using X-ray diffraction. The crystal structures of new compounds were probed using both analytical electron microscopy and X-ray diffraction. The c-axis of the misfit layer compound is perpendicular to the Substrate, with a c-axis lattice parameter that changes linearly with a slope of 0.612-0.615 nm as in is changed and n is held constant and with a slope of 0.654-0.656 nm as it is varied and m is held constant. The in-plane lattice parameters did not change as the individual layer thicknesses were increased and a misfit parameter of y = -0.01 was calculated, the first negative misfit parameter among known misfit layer compounds. Analytical electron microscopy images and X-ray diffraction data collected on mixed hkl reflections revealed rotational (turbostratic) disorder of the a-b planes.

Update: 11-Feb-2010

Title:
Phase separation in the CoO2 layer observed in thermoelectric layered cobalt dioxides
Authors:
Takami, T; Nanba, H; Umeshima, Y; Itoh, M; Nozaki, H; Itahara, H; Sugiyama, J Author Full Names: Takami, Tsuyoshi; Nanba, Hiroshi; Umeshima, Yasuhide; Itoh, Masayuki; Nozaki, Hiroshi; Itahara, Hiroshi; Sugiyama, Jun
Source:
PHYSICAL REVIEW B 81 (1): Art. No. 014401 JAN 2010
Abstract:
Co-59 nuclear magnetic resonance (NMR) measurements have been performed to study the local magnetic properties of the misfit layered cobalt dioxides (MLCO's) with the CoO2 and rock-salt layers, (Ca2CoO3)(0.62)CoO2 ( Ca3Co3.92O9.34) and Ca3Co3.92O9.34-delta with oxygen nonstoichiometry. The Co-59 NMR spectrum consists of mainly five lines at 4.2 K at which the samples are in a magnetically ordered state. Among the five NMR lines for Ca3Co3.92O9.34, three lines at higher frequencies (f's) satisfy the resonance condition with two branches indicating the presence of antiferromagnetic internal fields (H-int's). The other two lines exhibit one branch, and one of the two has a nonzero H-int under zero external field (ZF), which signifies the existence of ferromagnetic (FM) H-int's. The other has a zero H-int under ZF. By taking account of both the valence state of the Co ions in each layer and the lattice modulation due to the misfit between the CoO2 layer and the rock-salt layer, the NMR spectra at higher f's are attributed to the Co in the rock-salt layer, whereas those at lower f's to the Co in the CoO2 layer. Furthermore, a spin-density wave order appears to coexist with a FM order in the CoO2 layer for MLCO's. The magnetic and transport properties of these materials are discussed in terms of a separation between two phases.
Title:
Thermodynamics of multiferroic spin chains
Authors:
Sirker, J Author Full Names: Sirker, J.
Source:
PHYSICAL REVIEW B 81 (1): Art. No. 014419 JAN 2010
Abstract:
The minimal model to describe many spin-chain materials with ferroelectric properties is the Heisenberg model with ferromagnetic nearest-neighbor coupling J(1) and antiferromagnetic next-nearest-neighbor coupling J(2). Here we study the thermodynamics of this model using a density-matrix algorithm applied to transfer matrices. We find that the incommensurate spin-spin correlations-crucial for the ferroelectric properties and the analog of the classical spiral pitch angle-depend not only on the ratio J(2)vertical bar J(1)vertical bar but also strongly on temperature. We study small easy-plane anisotropies which can stabilize a vector chiral order as well as the finite-temperature signatures of multipolar phases, stable at finite magnetic field. Furthermore, we fit the susceptibilities of LiCuVO4, LiCu2O2, and Li2ZrCuO4. Contrary to the literature, we find that for LiCuVO4 the best fit is obtained with J(2) similar to 90 K and J(2)vertical bar J(1)vertical bar ! 0.5 and show that these values are consistent with the observed spin incommensurability. Finally, we discuss our findings concerning the incommensurate spin-spin correlations and multipolar orders in relation to future experiments on these compounds.
Title:
Anisotropic magnetic field responses of ferroelectric polarization in the trigonal multiferroic CuFe1-xAlxO2 (x=0.015)
Authors:
Nakajima, T; Mitsuda, S; Kanetsuki, S; Yamano, M; Iwamoto, S; Yoshida, Y; Mitamura, H; Sawai, Y; Tokunaga, M; Kindo, K; Prokes, K; Podlesnyak, A Author Full Names: Nakajima, Taro; Mitsuda, Setsuo; Kanetsuki, Shunsuke; Yamano, Motoyoshi; Iwamoto, Shunsuke; Yoshida, Yukihiko; Mitamura, Hiroyuki; Sawai, Yoshiki; Tokunaga, Masashi; Kindo, Koichi; Prokes, Karel; Podlesnyak, Andrey
Source:
PHYSICAL REVIEW B 81 (1): Art. No. 014422 JAN 2010
Abstract:
We have investigated magnetic field dependences of a ferroelectric incommensurate-helimagnetic order in a trigonal magnetoelectric multiferroic CuFe1-xAlxO2 with x=0.015, which exhibits the ferroelectric phase as a ground state, by means of neutron diffraction, magnetization, and dielectric polarization measurements under magnetic fields applied along various directions. From the present results, we have established the H-T magnetic phase diagrams for the three principal directions of magnetic fields; (i) parallel to the c axis, (ii) parallel to the helical axis, and (iii) perpendicular to the c and the helical axes. While the previous dielectric polarization (P) measurements on CuFe1-xGaxO2 with x=0.035 have demonstrated that the magnetic field dependence of the "magnetic domain structure" results in distinct magnetic field responses of P [S. Seki et al., Phys. Rev. Lett. 103, 237601 (2009)], the present study have revealed that the anisotropic! magnetic field dependence of the ferroelectric helimagnetic order "in each magnetic domain" can be also a source of a variety of magnetic field responses of P in CuFe(1-x)A(x)O(2) systems (A=Al, Ga).
Title:
Gutzwiller magnetic phase diagram of the undoped t-t '-U Hubbard model
Authors:
Markiewicz, RS; Lorenzana, J; Seibold, G Author Full Names: Markiewicz, R. S.; Lorenzana, J.; Seibold, G.
Source:
PHYSICAL REVIEW B 81 (1): Art. No. 014510 JAN 2010
Abstract:
We calculate the magnetic phase diagram of the half-filled t-t'-U Hubbard model as a function of t' and U, within the Gutzwiller approximation plus random-phase approximation. As U increases, the system first crosses over to one of a wide variety of incommensurate phases, whose origin is clarified in terms of double nesting. We evaluate the stability regime of the incommensurate phases by allowing for symmetry breaking with regard to the formation of spin spirals, and find a crossover to commensurate phases as U increases and a full gap opens. The results are compared with a variety of other recent calculations, and in general good agreement is found. For parameters appropriate to the cuprates, double occupancy should be only mildly suppressed in the absence of magnetic order, inconsistent with a strong-coupling scenario.
Title:
Charge-ordering transition and incommensurate antiphase structure of Fe2BO4 as seen via transmission electron microscopy
Authors:
Song, YJ; Yang, HX; Tian, HF; Ma, C; Qin, YB; Zeng, LJ; Shi, HL; Lu, JB; Li, JQ Author Full Names: Song, Y. J.; Yang, H. X.; Tian, H. F.; Ma, C.; Qin, Y. B.; Zeng, L. J.; Shi, H. L.; Lu, J. B.; Li, J. Q.
Source:
PHYSICAL REVIEW B 81 (2): Art. No. 020101 JAN 2010
Abstract:
The nature of the charge ordering (CO) in Fe2BO4 was carefully examined by in situ TEM observations from 360 K down to 20 K. An incommensurate structural modulation with the wave vector q = (1/2, 0, epsilon) becomes plainly visible in association with the CO transition at T-CO approximate to 340 K. Careful structural analysis suggests that this incommensurate structure originates from a well-defined Fe2+/Fe3+ ionic order along the FeO6 octahedral ribbons (in the a-axis direction) and from a discommensurate antiphase stripe order along the c-axis direction. The average periodicity of antiphase stripes changes notably with lowering temperature and, via certain intermediate states, toward a superstructure phase with modulation wave vector of q = (1/2, 0, 0) at similar to 150 K in association with a magnetic phase transition.
Title:
Solution growth of a binary icosahedral quasicrystal of Sc12Zn88
Authors:
Canfield, PC; Caudle, ML; Ho, CS; Kreyssig, A; Nandi, S; Kim, MG; Lin, X; Kracher, A; Dennis, KW; McCallum, RW; Goldman, AI Author Full Names: Canfield, P. C.; Caudle, M. L.; Ho, C-S.; Kreyssig, A.; Nandi, S.; Kim, M. G.; Lin, X.; Kracher, A.; Dennis, K. W.; McCallum, R. W.; Goldman, A. I.
Source:
PHYSICAL REVIEW B 81 (2): Art. No. 020201 JAN 2010
Abstract:
We report the discovery of a binary icosahedral phase in a Sc-Zn alloy obtained through solution-growth, producing millimeter-sized, facetted, single grain quasicrystals that exhibit different growth morphologies, pentagonal dodecahedra, and rhombic triacontahedra, under only marginally different growth conditions. These two morphologies manifest different degrees of quasicrystalline order. The discovery of i-Sc12Zn88 suggests that a re-examination of binary phase diagrams at compositions close to crystalline approximant structures may reveal other binary quasicrystalline phases.
Title:
Composition-dependent spin-phonon coupling in mixed crystals of the multiferroic manganite Eu1-xYxMnO3 (0 <= x <= 0.5) studied by Raman spectroscopy
Authors:
Issing, S; Pimenov, A; Ivanov, VY; Mukhin, AA; Geurts, J Author Full Names: Issing, S.; Pimenov, A.; Ivanov, V. Yu.; Mukhin, A. A.; Geurts, J.
Source:
PHYSICAL REVIEW B 81 (2): Art. No. 024304 JAN 2010
Abstract:
Yttrium substitution in Eu1-xYxMnO3 allows a quasicontinuous tuning of the lattice and magnetic properties of this multiferroic manganite without magnetic interference of rare-earth ions. In order to investigate the composition dependence of the spin-phonon coupling we employ polarized Raman scattering of orthorhombic mixed crystals of Eu1-xYxMnO3 (0 <= x <= 0.5) in the 10-300 K temperature range. Phonon frequency shifts and mode-mixing effects occur, depending on the average rare-earth ion radius determined by the concentration of Eu3+ and Y3+. Moreover, we observe a strong spin-phonon coupling with systematic composition dependence. It manifests itself as a mode-specific softening of the phonon modes in the temperature range of the magnetic ordered phases. The spin-phonon coupling is weakened for increasing Y contents but remains nonzero also in the incommensurate spiral magnetic phase, which occurs for 0.3 <= x <= 0.5. Thus for this class of manganites we report the observation of spin-phonon coupling in an ordered magnetic phase without ferromagnetic ordering within the MnO2 plane. Additionally for known sublattice magnetization quantitative values of the spin-phonon coupling constant are derived. Our results prove the suitability of phonons as a sensitive probe for the spin-spin correlation.
Title:
Critical properties of the unconventional spin-Peierls system TiOBr
Authors:
Clancy, JP; Gaulin, BD; Chou, FC Author Full Names: Clancy, J. P.; Gaulin, B. D.; Chou, F. C.
Source:
PHYSICAL REVIEW B 81 (2): Art. No. 024411 JAN 2010
Abstract:
We have performed detailed x-ray scattering measurements on single crystals of the spin-Peierls compound TiOBr in order to study the critical properties of the transition between the incommensurate spin-Peierls state and the paramagnetic state at T-C2 similar to 48 K. We have determined a value of the critical exponent beta which is consistent with the conventional three-dimensional universality classes, in contrast with earlier results reported for TiOBr and TiOCl. Using a simple power-law-fit function we demonstrate that the asymptotic critical regime in TiOBr is quite narrow, and obtain a value of beta(asy) = 0.32 +/- 0.03 in the asymptotic limit. A power-law-fit function which includes the first-order correction-to-scaling confluent singularity term can be used to account for data outside the asymptotic regime, yielding a more robust value of beta(avg) = 0.39 +/- 0.05. We observe no evidence of commensurate fluctuations above T-C1 in TiOBr, unlike its isostructural sister compound TiOCl. In addition, we find that the incommensurate structure between T-C1 and T-C2 is shifted in Q space relative to the commensurate structure below T-C1.
Title:
Tensile and creep behaviors of Mg-5Zn-2.5Er alloy improved by icosahedral quasicrystal
Authors:
Li, JH; Du, WB; Li, SB; Wang, ZH Author Full Names: Li, Jianhui; Du, Wenbo; Li, Shubo; Wang, Zhaohui
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 527 (4-5): 1255-1259 FEB 15 2010
Abstract:
The tensile and tensile creep properties of the as-cast Mg-5Zn-2.5Er (in wt.%) alloy strengthened by icosahedral quasicrystalline phase (1-phase) were studied. The Mg-5Zn-2.5Er alloy had better tensile properties both at room temperature and 175 degrees C than AE42 and Mg-5Zn alloys. Compared to AE42 alloy, the as-cast Mg-5Zn-2.5Er alloy had smaller steady-state creep rate and total creep strain under the creep conditions of 175 degrees C and 70 MPa for 100 h. The better creep resistance of the Mg-5Zn-2.5Er was mainly due to the formation of I-phase with high-thermal stability distributed along grain boundary. Moreover, microstructure analysis indicated that some fine precipitates in the alpha-Mg matrix can pin the dislocation effectively, improving the creep resistance of the alloy. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Directional magnetoelectric effects in MnWO4: magnetic sources of the electric polarization
Authors:
Toledano, P; Mettout, B; Schranz, W; Krexner, G Author Full Names: Toledano, P.; Mettout, B.; Schranz, W.; Krexner, G.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (6): Art. No. 065901 FEB 17 2010
Abstract:
The ferroelectric order and magnetic field induced effects observed in the spiral phase of MnWO4 are described theoretically. It is demonstrated explicitly that the Dzyaloshinskii-Moriya antisymmetric interactions contribute to the correlation between spins and electric dipoles in the incommensurate and commensurate ferroelectric phases of magnetic multiferroics. However, other single-site symmetric interactions are shown to be involved in the magnetoelectric process, suggesting the possible existence of an electric polarization originating from purely symmetric effects.
Title:
TEM study of a fluorite-type (1-x)Bi2O3 center dot xFe(2)O(3) superstructure in BiFeO3 ceramics synthesized by the rapid liquid-phase sintering method
Authors:
Guo, C; Pu, SZ; Chen, ZL; Li, MY; Cao, JF; Zou, HM Author Full Names: Guo, Chao; Pu, Shizhou; Chen, Zhenlian; Li, Meiya; Cao, Jiefeng; Zou, Huamin
Source:
CERAMICS INTERNATIONAL 36 (2): 507-512 MAR 2010
Abstract:
A commensurate modulated structure of (1 - x)Bi2O3 center dot xFe(2)O(3) is found in the BiFeO3 ceramics synthesized by the rapid liquid-phase sintering method. Transmission electron microscopy studies show that the superstructure is based on fluorite-type delta-Bi2O3 and modulated probably by oxygen vacancy ordering. The existence of such a superstructure may increase the leakage current of BiFeO3 ceramics. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Title:
Thermal hysteresis of ferroelectric transition in Sr4R2Ti4Nb6O30 (R=Sm and Eu) tetragonal tungsten bronzes
Authors:
Zhu, XL; Chen, XM Author Full Names: Zhu, X. L.; Chen, X. M.
Source:
APPLIED PHYSICS LETTERS 96 (3): Art. No. 032901 JAN 18 2010
Abstract:
Sr4R2Ti4Nb6O30 (R=Sm and Eu) tungsten bronze ceramics were prepared, and the dielectric properties and ferroelectric transition were investigated together with the crystal structure. A ferroelectric transition peak and a low temperature dielectric relaxation were observed from the curve of permittivity versus temperature during heating process for both ceramics. The ferroelectric transition indicated large thermal hysteresis during the heating and cooling cycles for both ceramics, where the ferroelectric transition peak disappeared during the cooling process, and the low temperature dielectric relaxation was obviously enhanced. Moreover, extremely large depression of the Curie-Weiss temperature (T-0) was observed in the present ceramics. These abnormal features were associated with the complex tetragonal tungsten bronze structure with two ferroelectrically active cations over two sets of sites and weak superstructure change from incommensurate to commensurate on cooling. The low temperature dielectric relaxation was due to the oxygen octahedron rotation in the ab plane and the possible compositional variations in the microscale.
Title:
A complicated quasicrystal approximant epsilon(16) predicted by the strong-reflections approach
Authors:
Li, MR; Sun, JL; Oleynikov, P; Hovmoller, S; Zou, XD; Grushko, B Author Full Names: Li, Mingrun; Sun, Junliang; Oleynikov, Peter; Hovmoller, Sven; Zou, Xiaodong; Grushko, Benjamin
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 17-26 Part 1 FEB 2010
Abstract:
The structure of a complicated quasicrystal approximant epsilon(16) was predicted from a known and related quasicrystal approximant epsilon(6) by the strong-reflections approach. Electron-diffraction studies show that in reciprocal space, the positions of the strongest reflections and their intensity distributions are similar for both approximants. By applying the strong-reflections approach, the structure factors of epsilon(16) were deduced from those of the known epsilon(6) structure. Owing to the different space groups of the two structures, a shift of the phase origin had to be applied in order to obtain the phases of epsilon(16). An electron-density map of epsilon(16) was calculated by inverse Fourier transformation of the structure factors of the 256 strongest reflections. Similar to that of epsilon(6), the predicted structure of epsilon(16) contains eight layers in each unit cell, stacked along the b axis. Along the b axis, epsilon(16) is built by banana-shaped tiles and pentagonal tiles; this structure is confirmed by high-resolution transmission electron microscopy (HRTEM). The simulated precession electron-diffraction (PED) patterns from the structure model are in good agreement with the experimental ones. epsilon(16) with 153 unique atoms in the unit cell is the most complicated approximant structure ever solved or predicted.
Title:
Structures of incommensurate and commensurate composite crystals Rb-x MnO2 (x=1.3711, 1.3636)
Authors:
Nuss, J; Pfeiffer, S; van Smaalen, S; Jansen, M Author Full Names: Nuss, Juergen; Pfeiffer, Steffen; van Smaalen, Sander; Jansen, Martin
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 27-33 Part 1 FEB 2010
Abstract:
Rb1.3711MnO2 (Rb11Mn8O16) has been synthesized via the azide/nitrate route from a stoichiometric mixture of the precursors Mn2O3, RbNO3 and RbN3. The structure of this extremely air- and moisture-sensitive compound can best be described in terms of an incommensurate composite structure, built up by a honeycomb-like framework of Rb ions, as one subsystem and by a second subsystem of chains, consisting of edge-sharing MnO4/2 tetrahedra. These two composite substructures interpenetrate in such a way that the manganate chain polyanions centre the channels of the Rb-honeycomb framework. Crystals transform by an aging process into Rb1.3636MnO2 (Rb15Mn11O22), which has a similar structure but a different commensurate modulation. Two reasons can be established for the origin of the modulations: the charge ordering of Mn2+/Mn3+ on one hand, and the incompatibility of the Mn-Mn and Rb-Rb separations on the other.

Update: 4-Feb-2010

Title:
Novel Geometrical Frustration Effects in the Two-Dimensional Triangular-Lattice Antiferromagnet NiGa2S4 and Related Compounds
Authors:
Nakatsuji, S; Nambu, Y; Onoda, S Author Full Names: Nakatsuji, Satoru; Nambu, Yusuke; Onoda, Shigeki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (1): Art. No. 011003 JAN 2010
Abstract:
Geometrical frustration may Suppress conventional magnetic long-range order and possibly promote a novel type of ordering associated with a higher order degree of freedom than spin dipolar-moment such as vector spin chirality and spin quadrupole moment. After a brief overview of such phenomena due to vector spin chirality, we focus on the two-dimensional (2D) frustrated magnetism in the layered chalcogenide Mott insulator NiGa2S4 and related compounds. NiGa2S4 provides the unique example of a S = 1 2D antiferromagnet on a regular exact triangular lattice. Extensive studies using high-purity samples of NiGa2S4 have revealed that Ni2+ S = 1 Heisenberg spins exhibit resonant critical slowing down at T* = 8.5 K without forming a magnetic long-range order, Signaling a viscous spin-liquid state. The critical spin-fluctuation regime extends over almost all order of magnitude in temperature both above and below T. Even well below T, the spin-spin correlation remains short-ranged at an incommensurate wave vector close to (1/6, 1/6,0), corresponding to a 120 degrees correlation with 2a period. Interestingly, however, a 2D linearly dispersive magnetic mode and a quasi-static spin component exist in the low temperature limit. Possibly relevant scenarios including topological phase transition associated with Z(2) vortex due to vector spin chirality, Spill quadrupolar nematic correlation, and C-3 bond-ordering are reviewed.
Title:
Sliding Friction of Kr Films Adsorbed on Graphite
Authors:
Kobayashi, H; Taniguchi, J; Suzuki, M; Miura, K; Arakawa, I Author Full Names: Kobayashi, Hajime; Taniguchi, Junko; Suzuki, Masaru; Miura, Kouji; Arakawa, Ichiro
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 (1): Art. No. 014602 JAN 2010
Abstract:
We have carried Out quartz crystal microbalance (QCM) experiments for Kr films adsorbed on exfoliated graphite from a single crystal, and have examined the coverage dependence of the sliding friction and the depinning transition up to the bilayer film. For the monolayer film, the coupled mass density appears at the commensurate and fluid (C+F) phase. An increase of this density starts at the commensurate (C) phase and continues at the incommensurate (IC) phase after the C-IC transition. It was found that the monolayer film slides not uniformly but partly on the substrate, and that the slip time is 60 ns at the C phase. On the other hand, the film around the layer completion slides almost uniformly, and its slip time is about 10 ns. For the bilayer film, the experimental data are reasonably explained by a model in which the slip occurs at the boundary between the first and second atomic layers, in addition to the boundary between the film and the substrate. For the oscillation amplitude sweep at a constant coverage, a rapid change in frequency was observed for the monolayer and bilayer films, which is attributed to the depinning transition. This magnitude takes the minimum value around the layer completion.
Title:
Low temperature incommensurately modulated and noncollinear spin structure in FeCr2S4
Authors:
Kalvius, GM; Krimmel, A; Hartmann, O; Wappling, R; Wagner, FE; Litterst, FJ; Tsurkan, V; Loidl, A Author Full Names: Kalvius, G. M.; Krimmel, A.; Hartmann, O.; Wappling, R.; Wagner, F. E.; Litterst, F. J.; Tsurkan, V.; Loidl, A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (5): Art. No. 052205 FEB 10 2010
Abstract:
FeCr2S4 orders magnetically at T-N approximate to 170 K. According to neutron diffraction, the ordered state down to 4.2 K is a simple collinear ferrimagnet maintaining the cubic spinel structure. Later studies, however, claimed trigonal distortions below similar to 60 K coupled to the formation of a spin glass type ground state. To obtain further insight, muon spin rotation/relaxation (mu SR) spectroscopy was carried out between 5 and 200 K together with new Fe-57 Mossbauer measurements. Below similar to 50 K, our data point to the formation of an incommensurately modulated noncollinear spin arrangement like a helical spin structure. Above 50 K, the spectra are compatible with collinear ferrimagnetism, albeit with a substantial spin disorder on the scale of a few lattice constants. These spin lattice distortions become very large at 150 K and the magnetic state is now better characterized as consisting of rapidly fluctuating short-range ordered spins. The Neel transition is of second order, but ill defined, extending over a range of similar to 10 K. The Mossbauer data around 10 K confirm the onset of orbital freezing and are also compatible with the noncollinear order of iron. The absence of a major change in the quadrupole interaction around 50 K renders the distortion of crystal symmetry to be small.
Title:
EVAL15: a diffraction data integration method based on ab initio predicted profiles
Authors:
Schreurs, AMM; Xian, XY; Kroon-Batenburg, LMJ Author Full Names: Schreurs, Antoine M. M.; Xian, Xinyi; Kroon-Batenburg, Loes M. J.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 70-82 Part 1 FEB 2010
Abstract:
A novel diffraction data integration method is presented, EVAL15, based upon ab initio calculation of three-dimensional (x, y, omega) reflection profiles from a few physical crystal and instrument parameters. Net intensities are obtained by least-squares fitting the observed profile with the calculated standard using singular value decomposition. This paper shows that profiles can be predicted satisfactorily and that accurate intensities are obtained. The detailed profile analysis has the additional advantage that specific physical properties of the crystal are revealed. The EVAL15 method is particularly useful in circumstances where other programs fail, such as regions of reciprocal space with weak scattering, crystals with anisotropic shape or anisotropic mosaicity, K alpha(1)/K alpha(2) peak splitting, interference from close neighbours, twin lattices, or satellite reflections of modulated structures, all of which may frustrate the customary profile learning and fitting procedures. EVAL15 allows the deconvolution of overlapping reflections.
Title:
Ab initio structure solution by iterative phase-retrieval methods: performance tests on charge flipping and low-density elimination
Authors:
Fleischer, F; Weber, T; Deloudi, S; Palatinus, L; Steurer, W Author Full Names: Fleischer, Frank; Weber, Thomas; Deloudi, Sofia; Palatinus, Lukas; Steurer, Walter
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 89-100 Part 1 FEB 2010
Abstract:
Comprehensive tests on the density-modification methods charge flipping [Oszlanyi & Suto (2004). Acta Cryst. A60, 134-141] and low-density elimination [Shiono & Woolfson (1992). Acta Cryst. A48, 451-456] for solving crystal structures are performed on simulated diffraction data of periodic structures and quasicrystals. A novel model-independent figure of merit, which characterizes the reliability of the retrieved phase of each reflection, is introduced and tested. The results of the performance tests show that the quality of the phase retrieval highly depends on the presence or absence of an inversion center and on the algorithm used for solving the structure. Charge flipping has a higher success rate for solving structures, while low-density elimination leads to a higher accuracy in phase retrieval. The best results can be obtained by combining the two methods, i.e. by solving a structure with charge flipping followed by a few cycles of low-density elimination. It is shown that these additional cycles dramatically improve the phases not only of the weak reflections but also of the strong ones. The results can be improved further by averaging the results of several runs and by applying a correction term that compensates for a reduction of the structure-factor amplitudes by averaging of inconsistently observed reflections. It is further shown that in most cases the retrieved phases converge to the best solution obtainable with a given method.
Title:
An electron diffraction and Monte Carlo simulation study of an incommensurate antiferroelectric state in the relaxor ferroelectric Pb2ScTaO6
Authors:
Baba-Kishi, KZ; Pasciak, M Author Full Names: Baba-Kishi, K. Z.; Pasciak, M.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 140-150 Part 1 FEB 2010
Abstract:
Incommensurate satellite reflections modulating along the < 110 >* directions have been observed in the electron diffraction patterns of single crystals of the relaxor ferroelectric Pb2ScTaO6 (PST) recorded via transmission electron microscopy. The satellites occur characteristically within a specific temperature range and display differing or variable modulation vectors relative to their primary reflections. The satellites represent a weak frustrated antiferroelectric state in PST, termed the incommensurate antiferroelectric (IAFE) state. The observed IAFE state coexists with the ferroelectric and paraelectric states within a specific temperature regime and is dynamic in nature, meaning that the dispositions of the satellites can be altered by varying the temperature applied to the crystal, in-situ in the transmission electron microscope. The observed satellites are associated with thin, needle-shaped, closely packed striated domains of about 5-15 nm in width. The satellites appear exclusively in crystals of PST with an advanced degree of 1:1 chemical long-range order, exceeding 90%. The satellites and their domains are interpreted as originating from a displacive, antiferroelectric coupling of the ions, driven in particular by the Pb ions. The Monte Carlo (MC) method was used exhaustively to evaluate the structural regimes that lead to the occurrence of the IAFE state. In the MC simulations, the displacements were correlated with the ferroelectric and antiferroelectric couplings, resulting in the IAFE domains and their associated satellites of differing dispositions or modulation vectors. The results of the MC simulations agree well with the electron diffraction observations, supporting the model of an antiferroelectric displacement with an incommensurate modulation of the Pb ions in the < 110 >* directions.
Title:
EXTRAX: an ImageJ plug-in for electron diffraction intensity extraction
Authors:
Dorcet, V; Larose, X; Fermin, C; Bissey, M; Poullay, P Author Full Names: Dorcet, V.; Larose, X.; Fermin, C.; Bissey, M.; Poullay, P.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 43: 191-195 Part 1 FEB 2010
Abstract:
A plug-in (EXTRAX) has been developed for ImageJ - a public domain Java-based program widely used for image processing and analysis in microscopy. This plug-in allows the extraction and measurement of intensities from electron diffraction spot patterns with a semi-automatic peak location based on a two-dimensional lattice given by the user. It is also possible to take into account supplementary spots originating from high-order Laue zones and/or the existence of a modulation vector.

Update: 29-Jan-2010

Title:
LaSe1.85, CeSe1.83, NdSe1.83 and SmSe1.84 - four new rare earth metal polyselenides with incommensurate site occupancy and displacive modulation
Authors:
Graf, C; Doert, T Author Full Names: Graf, Christian; Doert, Thomas
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 224 (12): 568-579 2009
Abstract:
Crystals of the four new binary rare earth metal polyselenides LaSe1.85, CeSe1.83, NdSe1.83 and SMSe1.84 were obtained by flux reactions. Their two-dimensionally incommensurately modulated structures were solved from X-ray diffraction data. Structure models were established in super space group X4/n(-alpha beta 0)(beta alpha 0)00 with modulation wave vectors q(1) = -alpha a* + beta b* and q(2) = beta a* + alpha b* and the centering vector (0, 0, 1/2, 1/2, 1/2). The unit cell parameters at T = 293 K are a = 4.216(1) angstrom and c = 17.048(2) angstrom for LaSe1.85, a = 4.178(1) angstrom and c = 16.942(3) angstrom for CeSe1.83, a = 4.123(1) angstrom and c = 16.792(2) angstrom for NdSe1.83 and a = 4.080(1) angstrom and c = 16.672(2) angstrom for SmSe1.84; the components of the modulation wave vectors are alpha = beta = 0.292(1) for LaSe1.85 and CeSe1.83, and alpha = beta = 0.293(1) for NdSe1.83 and SmSe1.84, respectively. The modulation originates from a site occupancy wave caused by defects in planar selenium layers coupled to a displacive modulation.
Title:
Interfacial reaction between Al72Ni12Co16 decagonal quasicrystalline particles and liquid aluminium
Authors:
Cheng, SL; Yang, GC; Wang, JC; Liu, F; Zhu, M; Zhou, YH Author Full Names: Cheng, Suling; Yang, Gencang; Wang, Jincheng; Liu, Feng; Zhu, Man; Zhou, Yaohe
Source:
JOURNAL OF MATERIALS SCIENCE 45 (6): 1438-1442 MAR 2010
Abstract:
The interfacial reaction between Al72Ni12Co16 quasicrystalline particles and pure Al melt at 670 A degrees C was investigated. For all the studied samples, only one interfacial reaction product was detected at the interface by scanning electron microscopy. The product was identified to be the Al-9(Co, Ni)(2) crystalline phase, which show an rod-like morphology. The growth rate of the Al-9(Co, Ni)(2) phase layer is very fast. Based on the microstructure analysis results, it is proposed that the layer growth is initially towards the liquid phase, but changes direction towards the quasicrystalline phase by the solid state reaction of diffusional Al with the quasicrystalline phase at the Al72Ni12Co16/Al-9(Co, Ni)(2) interface. A grain boundary grooving effect is deduced to have been involved during the reaction process.

Update: 22-Jan-2010

Title:
STRUCTURE AND PROPERTIES FEATURES OF Ti-Zr-Ni-QUASICRYSTALS
Authors:
Azhazha, VM; Malykhin, SV; Merisov, BA; Pugachov, AT; Khadzhay, GY Author Full Names: Azhazha, V. M.; Malykhin, S. V.; Merisov, B. A.; Pugachov, A. T.; Khadzhay, G. Ya
Source:
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY (6): 115-126 Part 3 2009
Abstract:
For Ti-Zr-Ni ingots prepared by equilibrium crystallization, and 20 to 100 mu m ribbons obtained by rapid quenching on the same disc, the dependence of phase composition on the super-pure components charge mixture composition and on the disc velocity has been studied. The technology parameters for synthesis of QC single-phase structures or ones with prevailing portion of icosahedral quasicrystalline structure were determined. The peculiarities of structure,. substructure and stress state of the ribbons were studied. Through the ribbon section, the gradient variations of phase composition, grain size, micro-and nano-hardness, Young modulus, structure and substructure parameters, and residual stress level were established. The gradient distributions depend on the quenching speed. The temperature behaviour of electrical resistivity without external magnetic field and under magnetic field was investigated. The transition to superconductivity state was found. The properties o! f hydrogen accumulation and the parameters of its diffusion, as well as mechanical properties and deformation features, and thermo-physical properties of Ti-Zr-Ni quasicrystals were studied. The evolution of structure and stress state in quasicrystals as a result of thermal influence, hydrogen saturation, and irradiation was analyzed.
Title:
A neutron powder diffraction study of the helimagnetic structure of TlCo2Se2-xSx
Authors:
Ronneteg, S; Berger, R; Andre, G Author Full Names: Ronneteg, Sabina; Berger, Rolf; Andre, Gilles
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (6): 681-685 MAR 2010
Abstract:
The magneti clayer structure of TlCo2Se2-xSx has been thoroughly re-investigated with neutron powder diffraction. The cobalt magnetic moments are ferromagnetically arranged with in the layers, but the interlayer coupling differs profoundly with varying composition (x): the spins in TlCo2Se2 form a helix along the c-axis with a turning-angle of similar to 119 degrees at 1.4 K. This kind of helical structure prevails for 0 <= x <= 1.5 with a gradual decrease of the angle with increasing sulphur content, down to 34 degrees, showing an almost linear relationship with the interlayer distance of Co-Co. For x >= 1.75 the interlayer couplingchanges to ferromagnetic. Unexpectedly, two helices were found to coexist at x = 0.5 and x = 1.0. The interaction between adjacent cobalt layers is there characterized by an incommensurate angle (106 degrees, resp., 73 degrees) together with a commensurate angle of 90 degrees. The magnetic structures have been refined as two magnetic phases, each having a characteristic wave vector. A tentative model where the symmetry of the structure and the interlayer distance compete is considered for explaining the simultaneous occurrence of the two kinds of diffraction profile satellites. (C) 2009 Elsevier B. V. All rights reserved.

Update: 14-Jan-2010

Title:
Exploring low-energy landscape of quasi-one-dimensional conductors by heat relaxation and magnetic field
Authors:
Biljakovic, K; Lasjaunias, JC; Melin, R; Monceau, P; Remenyi, G; Sahling, S; Staresinic, D Author Full Names: Biljakovic, K.; Lasjaunias, J. C.; Melin, R.; Monceau, P.; Remenyi, G.; Sahling, S.; Staresinic, D.
Source:
SYNTHETIC METALS 159 (21-22): 2402-2405 Sp. Iss. SI NOV 2009
Abstract:
Modulated charge or spin superstructures of organic quasi-one-dimensional conductors exhibit specific low-energy excitations (LEE) at very low temperatures due to metastable states caused by strong pinning centers. These phase excitations (soliton-like topological defects) demonstrate rich and unexpected properties in a magnetic field, due to their magnetic moments. We discuss mainly on the dynamical aspects related to the non-equilibrium phenomena measured in heat relaxation below 1 K. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Magnetoelectric Response of Multiferroic BiFeO3 and Related Materials from First-Principles Calculations
Authors:
Wojdel, JC; Iniguez, J Author Full Names: Wojdel, Jacek C.; Iniguez, Jorge
Source:
PHYSICAL REVIEW LETTERS 103 (26): Art. No. 267205 DEC 31 2009
Abstract:
We present a first-principles scheme for computing the magnetoelectric response of multiferroics. We apply our method to BiFeO3 (BFO) and related compounds in which Fe is substituted by other magnetic species. We show that under certain relevant conditions-i.e., in the absence of incommensurate spin modulation, as in BFO thin films and some BFO-based solid solutions-these materials display a large linear magnetoelectric response. Our calculations reveal the atomistic origin of the coupling and allow us to identify the most promising strategies to enhance it.
Title:
Elastic behavior associated with phase transitions in incommensurate Ba2NaNb5O15
Authors:
Herrero-Albillos, J; Marchment, P; Salje, EKH; Carpenter, MA; Scott, JF Author Full Names: Herrero-Albillos, J.; Marchment, P.; Salje, E. K. H.; Carpenter, M. A.; Scott, J. F.
Source:
PHYSICAL REVIEW B 80 (21): Art. No. 214112 DEC 2009
Abstract:
The elastic behavior of barium sodium niobate (Ba2NaNb5O15) has been investigated by resonant ultrasound spectroscopy through six different structural phases, with emphasis on the five incommensurate phase transitions near 40, 110, 547, 565, and 582 K. Data near 40 K are at least consistent with the existence of a lock-in transition to P4nm at that temperature [Filipic , J. Phys.: Condens. Matter 19, 236206 (2007)], which has been controversial. A relaxation process occurs around the transition near 110 K and is assigned to a process involving movement of domain walls of the phase. Unusual behavior is observed through the high-temperature incommensurate transitions with large variations in frequency in the ultrasonic resonances, and a broad peak in the dissipation. No clear signature of the 1q-2q incommensurate-incommensurate transition at 565 K is observed. This is compatible with a model in which incommensurate-incommensurate transitions are not expected to manifest elastic anomalies.
Title:
Magnetism at surfaces and defects in icosahedral Al-Pd-Mn quasicrystals
Authors:
Krajci, M; Hafner, J Author Full Names: Krajci, M.; Hafner, J.
Source:
PHYSICAL REVIEW B 80 (21): Art. No. 214419 DEC 2009
Abstract:
In our recent work [Krajcciacute and Hafner, Phys. Rev. B 78, 224207 (2008)] we have demonstrated that the ground state of bulk i-Al-Pd-Mn quasicrystals is nonmagnetic. Mn atoms located at specific sites can acquire a large magnetic moment if they have at least two Pd neighbors in the first coordination shell. Such configurations can be created by substitutional Al/Pd defects which can be formed at low energetic cost because at these sites the overlap between the pseudo-Mackay and Bergman clusters building the quasicrystalline structure leads to conflicting assignments of the chemical decoration. Besides the large magnetic moments formed on these special Mn sites, we have found a broad diffuse background of smaller magnetic moments on many different Mn atoms induced by the large Mn moments. In the present work we extend these investigations to magnetism at the five-fold surface of the quasicrystal and at isolated point defects with particular attention to the formati! on of induced moments. For the stable five-fold surface we find that Mn atoms located in the surface layer carry indeed large magnetic moments of up to 3 mu(B) and that smaller magnetic moments (aligned both parallel and antiparallel to the surface moments) are induced at distances of up to 10 A degrees below the surface. We have considered three types of isolated point defects (and substitutional defects) around a Mn atom and investigated the formation of magnetic moments on the Mn atom and of induced moments on the surrounding sites. For both the magnetization induced below a magnetic surface and the magnetization induced around an Al/Pd substitutional defect, the induced moments show an irregular dependence on the distance from the inducing "source" moment, but a marked dependence on the location of the Mn atom in the occupation domain in six-dimensional hyperspace. Mn atoms with a large coordinate in perpendicular space show large induced moments. Based on the analysis of the local paramagnetic density of states we demonstrate that the formation of a large induced moment is caused by a large polarizability of these Mn atoms, which is related in turn to a rather loosely packed local environment. Per Mn atom, the sum of the source moment (created by a special substitutional defect in the bulk quasicrystal or by the reduced coordination of a Mn atom at the surface) and of the induced moments reaches values of 6 to 8 mu(B), i.e., much higher than the limit set by Hund's rule for the spin moment of a free Mn atom.
Title:
Multiferroicity and spiral magnetism in FeVO4 with quenched Fe orbital moments
Authors:
Daoud-Aladine, A; Kundys, B; Martin, C; Radaelli, PG; Brown, PJ; Simon, C; Chapon, LC Author Full Names: Daoud-Aladine, A.; Kundys, B.; Martin, C.; Radaelli, P. G.; Brown, P. J.; Simon, C.; Chapon, L. C.
Source:
PHYSICAL REVIEW B 80 (22): Art. No. 220402 DEC 2009
Abstract:
FeVO4 has been studied by heat capacity, magnetic susceptibility, electric polarization and single-crystal neutron-diffraction experiments. The triclinic crystal structure is made of S-shaped clusters of six Fe3+ ions, linked by VO43- groups. Two long-range magnetic ordering transitions occur at T-N1=22 K and T-N2=15 K. Both magnetic structures are incommensurate and below T-N2, FeVO4 becomes weakly ferroelectric coincidentally with the loss of the collinearity of the magnetic structure in a very similar fashion than in the classical TbMnO3 multiferroic material. However we argue that the symmetry considerations and the mechanisms invoked to explain these properties in TbMnO3 do not straightforwardly apply to FeVO4. First, the magnetic structures, even the collinear structure, are all acentric so that ferroelectricity in FeVO4 is not correlated with the fact magnetic ordering is breaking inversion symmetry. Regarding the mechanism, FeVO4 has quenched orbital moments that questions the exact role of the spin-orbit interactions.
Title:
Comparative study on internal friction in an Al-Pd-Mn icosahedral quasicrystal and its crystal approximants
Authors:
So, YG; Sato, S; Edagawa, K; Mori, T; Tamura, R Author Full Names: So, Yeong-Gi; Sato, Shun; Edagawa, Keiichi; Mori, Takahiro; Tamura, Ryuji
Source:
PHYSICAL REVIEW B 80 (22): Art. No. 224204 DEC 2009
Abstract:
The internal friction was measured for an Al-Pd-Mn icosahedral phase (i-phase) and its 1/1 and 2/1 approximant phases in an Al-Pd-Mn-Si system in a forced flexural-oscillation mode in a frequency range of 0.05-20 Hz and a temperature range of 300-873 K. For the i-phase, large and small absorption peaks were observed with Q(-1)approximate to 1.3x10(-2) and 8x10(-4), respectively. These two peaks were absent for the 1/1-phase, which showed two other peaks instead. The 2/1-phase exhibited the features of both the i and 1/1-phases; it showed two peaks of the i-phase and one of the two peaks of the 1/1-phase. All the observed peaks were of the thermally activated relaxation type, and their activation enthalpies and frequency factors were evaluated. The larger peak of the i-phase, which was absent for the 1/1-phase and present with a much reduced intensity for the 2/1-phase, was shown to result from a relaxation process involving collective atomic motion. Collective and correl! ated phason jumps were discussed as a possible mechanism for it. It was speculated that the other peaks observed only for the approximant phases are due to Zener relaxations by the reorientation of atom pairs involving Si.
Title:
Excitation spectrum and magnetic field effects in a quantum critical spin-orbital system: The case of FeSc2S4
Authors:
Chen, G; Schnyder, AP; Balents, L Author Full Names: Chen, Gang; Schnyder, Andreas P.; Balents, Leon
Source:
PHYSICAL REVIEW B 80 (22): Art. No. 224409 DEC 2009
Abstract:
The orbitally degenerate A-site spinel compound FeSc2S4 has been experimentally identified as a "spin-orbital liquid," with strong fluctuations of both spins and orbitals. Assuming that the second-neighbor spin-exchange J(2) is the dominant one, we argued in a recent theoretical study [G. Chen , Phys. Rev. Lett. 102, 096406 (2009)] that FeSc2S4 is in a local "spin-orbital singlet" state driven by spin-orbit coupling, close to a quantum critical point, which separates the spin-orbital singlet phase from a magnetically and orbitally ordered phase. In this paper, we refine further and develop this theory of FeSc2S4. First, we show that inclusion of a small first-neighbor exchange J(1) induces a narrow region of incommensurate phase near the quantum critical point. Next, we derive the phase diagram in the presence of an external magnetic field B, and show that the latter suppresses the ordered phase. Lastly, we compute the field-dependent dynamical magnetic susceptibility chi(k,omega;B), from which we extract a variety of physical quantities. Comparison with and suggestions for experiment are discussed.
Title:
Kinetic magnetism and orbital order in iron telluride
Authors:
Turner, AM; Wang, F; Vishwanath, A Author Full Names: Turner, Ari M.; Wang, Fa; Vishwanath, Ashvin
Source:
PHYSICAL REVIEW B 80 (22): Art. No. 224504 DEC 2009
Abstract:
Iron telluride (FeTe), a relative of the iron-based high-temperature superconductors, displays unusual magnetic order and structural transitions. Here, we explore the idea that strong correlations may play an important role in these materials. We argue that the unusual orders observed in FeTe can be understood from a picture of correlated local moments with orbital degeneracy, coupled to a small density of itinerant electrons. A component of the structural transition is attributed to orbital, rather than magnetic ordering, introducing a strongly anisotropic character to the system along the diagonal directions of the iron lattice. Double exchange interactions couple the diagonal chains leading to the observed ordering wave vector. The incommensurate order in samples with excess iron arises from electron doping in this scenario. The strong anisotropy of physical properties in the ordered phase should be detectable by transport in single domains. Predictions for ARPES, inelastic neutron scattering and hole/electron doping studies are also made.
Title:
Pokrovsky-Talapov model at finite temperature: A renormalization-group analysis
Authors:
Lazarides, A; Tieleman, O; Smith, CM Author Full Names: Lazarides, A.; Tieleman, O.; Smith, C. Morais
Source:
PHYSICAL REVIEW B 80 (24): Art. No. 245418 DEC 2009
Abstract:
We calculate the finite-temperature shift of the critical wave vector Q(c) of the Pokrovsky-Talapov model using a renormalization-group analysis. Separating the Hamiltonian into a part that is renormalized and one that is not, we obtain the flow equations for the stiffness and an arbitrary potential. We then specialize to the case of a cosine potential, and compare our results to well-known results for the sine-Gordon model, to which our model reduces in the limit of vanishing driving wave vector Q=0. Our results may be applied to describe the commensurate-incommensurate phase transition in several physical systems and allow for a more realistic comparison with experiments, which are always carried out at a finite temperature.
Title:
Hyperfine Fields and Magnetic Structure in the B Phase of CeCoIn5
Authors:
Curro, NJ; Young, BL; Urbano, RR; Graf, MJ Author Full Names: Curro, Nicholas J.; Young, Ben-Li; Urbano, Ricardo R.; Graf, Matthias J.
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS 158 (3-4): 635-646 FEB 2009
Abstract:
We re-analyze Nuclear Magnetic Resonance (NMR) spectra observed at low temperatures and high magnetic fields in the field-induced B phase of CeCoIn5. The NMR spectra are consistent with incommensurate antiferromagnetic order of the Ce magnetic moments. However, we find that the spectra of the In(2) sites depend critically on the direction of the ordered moments, the ordering wavevector and the symmetry of the hyperfine coupling to the Ce spins. Assuming isotropic hyperfine coupling, the NMR spectra observed for H parallel to [100] are consistent with magnetic order with wavevector Q = pi (1+delta/a, 1/a, 1/c) and Ce moments ordered antiferromagnetically along the [100] direction in real space. If the hyperfine coupling has dipolar symmetry, then the NMR spectra require Ce moments along the [ 001] direction. The dipolar scenario is also consistent with recent neutron scattering measurements that find an ordered moment of 0.15 mu(B) along [001] and Q(n) = pi(1+delta/a, 1+delta/a, 1/c) with in-commensuration delta = 0.12 for field H parallel to [1 (1) over bar0]. Using these parameters, we find that a hyperfine field with dipolar contribution is consistent with findings from both experiments. We speculate that the B phase of CeCoIn5 represents an intrinsic phase of modulated superconductivity and antiferromagnetism that can only emerge in a highly clean system.
Title:
Observation of two separate charge density wave transitions in Gd2Te5 via transmission electron microscopy and high-resolution X-ray diffraction
Authors:
Shin, KY; Ru, N; Fisher, IR; Condron, CL; Toney, MF; Wu, YQ; Kramer, MJ Author Full Names: Shin, K. Y.; Ru, N.; Fisher, I. R.; Condron, C. L.; Toney, M. F.; Wu, Y. Q.; Kramer, M. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 489 (2): 332-335 JAN 21 2010
Abstract:
Gd2Te5 is a layered material consisting of alternating single and double square planar Te sheets. At room temperature the material hosts a complex lattice modulation characterized by multiple in-plane wavevectors. Diffraction measurements performed via transmission electron microscopy and high-resolution X-ray scattering reveal two distinct transitions at T-c1 = 410(3) and T-c2 = 532(3) K, associated with an on-axis incommensurate lattice modulation and an off-axis commensurate lattice modulation respectively. Our results show that the two lattice modulations are separate in origin but that there is some coupling between them. (C) 2009 Elsevier B.V. All rights reserved.

Update: 7-Jan-2010

Title:
First-Principles Modeling of Multiferroic RMn2O5
Authors:
Cao, K; Guo, GC; Vanderbilt, D; He, LX Author Full Names: Cao, Kun; Guo, Guang-Can; Vanderbilt, David; He, Lixin
Source:
PHYSICAL REVIEW LETTERS 103 (25): Art. No. 257201 DEC 18 2009
Abstract:
We investigate the phase diagrams of RMn2O5 via a first-principles effective-Hamiltonian method. We are able to reproduce the most important features of the complicated magnetic and ferroelectric phase transitions. The calculated polarization as a function of temperature agrees very well with experiments. The dielectric-constant step at the commensurate-to-incommensurate magnetic phase transition is well reproduced. The microscopic mechanisms for the phase transitions are discussed.
Title:
Electric Control of Spin Helicity in Multiferroic Triangular Lattice Antiferromagnet CuCrO2 with Proper-Screw Order
Authors:
Soda, M; Kimura, K; Kimura, T; Matsuura, M; Hirota, K Author Full Names: Soda, Minoru; Kimura, Kenta; Kimura, Tsuyoshi; Matsuura, Masato; Hirota, Kazuma
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (12): Art. No. 124703 DEC 2009
Abstract:
We have carried out a spin-polarized-neutron study on multiferroic CuCrO2 to clarify the origin of the ferroelectricity. The neutron results demonstrate that an incommensurate proper-screw magnetic structure of CuCrO2 induces electric polarization. Not only the magnetic structure but also the oxygen location contributes to the ferroelectricity of CuCrO2. The electric polarization of CuCrO2 can be explained not by a conventional spin-current model but by a theoretical prediction proposed by Arima. The spin helicities of CuCrO2 can be reversed by the reversal of the electric field E in the multiferroic phase.
Title:
Coexistence of the antiferromagnetic and superconducting order and its effect on spin dynamics in electron-doped high-T-c cuprates
Authors:
Chen, CP; Jiang, HM; Li, JX Author Full Names: Chen, Cui-Ping; Jiang, Hong-Min; Li, Jian-Xin
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (3): Art. No. 035701 JAN 27 2010
Abstract:
In the framework of the slave-boson approach to the t-t'-t ''-J model, it is found that for electron-doped high-T-c cuprates, the staggered antiferromagnetic (AF) order coexists with the superconducting (SC) order in a wide doping level ranged from underdoped to nearly optimally doped at the mean-field level. In the coexisting phase, it is revealed that the spin response is commensurate in a substantial frequency range below a crossover frequency omega(c) for all dopings considered, and it switches to the incommensurate structure when the frequency is higher than omega(c). This result is in agreement with the experimental measurements. Comparison of the spin response between the coexisting phase and the pure SC phase with a d(x2-y2)-wave pairing plus a higher harmonics term (DP + HH) suggests that the inclusion of the two-band effect is important to consistently account for both the dispersion of the spin response and the non-monotonic gap behavior in the electron-doped cuprates.
Title:
The modulated structure and ferromagnetic insulating state in a nine-layer BaRuO3
Authors:
Du, CH; Yao, CH; Ling, DC; Tang, MT; Hsu, FC; Liu, HL; Hatton, PD; Ikeda, N Author Full Names: Du, Chao-Hung; Yao, Chang-Hung; Ling, Dah-Chin; Tang, Mau-Tsu; Hsu, Fon-Chi; Liu, Hsiang-Lin; Hatton, P. D.; Ikeda, Naoshi
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (3): Art. No. 036003 JAN 27 2010
Abstract:
We report the observation of a modulated structure and a ferromagnetic insulating state in a high quality single crystal of a nine-layer BaRuO3. Using x-ray scattering, the modulated satellites were observed to double the unit cell along the c-axis at low temperature. The ferromagnetic insulating state is confirmed by magnetic and resistivity measurements. Analyzing the peak profiles from the modulation and host structure respectively, showed a lattice distortion at T similar to 55 K. These findings elucidate the intimate relationship between ferromagnetism and lattice distortion in a nine-layer BaRuO3.
Title:
Evidence for a Self-bound Liquid State and the Commensurate-Incommensurate Coexistence in 2D He-3 on Graphite
Authors:
Sato, D; Tsuji, D; Takayoshi, S; Obata, K; Matsui, T; Fukuyama, H Author Full Names: Sato, D.; Tsuji, D.; Takayoshi, S.; Obata, K.; Matsui, T.; Fukuyama, Hiroshi
Source:
JOURNAL OF LOW TEMPERATURE PHYSICS 158 (1-2): 201-206 Sp. Iss. SI JAN 2010
Abstract:
We made heat-capacity measurements of two dimensional (2D) He-3 adsorbed on graphite preplated with monolayer He-4 in a wide temperature range (0.1 <= T <= 80 mK) at densities higher than that for the 4/7 phase (= 6.8 nm(-2)). In the density range of 6.8 <= rho <= 8.1 nm(-2), the 4/7 phase is stable against additional 3He atoms up to 20% and they are promoted into the third layer. We found evidence that such promoted atoms form a self-bound 2D Fermi liquid with an approximate density of 1 nm(-2) from the measured density dependence of the gamma-coefficient of heat capacity. We also show evidence for the first-order transition between the commensurate 4/7 phase and the ferromagnetic incommensurate phase in the second layer in the density range of 8.1 <= rho <= 9.5 nm(-2).
Title:
Growth of large single-grain quasicrystals in the Ag-In-Yb system by Bridgman method
Authors:
Cui, C; Tsai, AP Author Full Names: Cui, Can; Tsai, An Pang
Source:
JOURNAL OF CRYSTAL GROWTH 312 (1): 131-135 DEC 15 2009
Abstract:
Well-defined single-grain Ag-In-Yb icosahedral quasicrystals of order of centimeter have been grown by the Bridgman method. The scanning electron microscopy (SEM) observation showed that the compositional distribution in the single-grain quasicrystals is uniform and Laue X-ray diffraction measurements verified the formation of single-grain icosahedral quasicrystals. The natural growth direction of the single-grain quasicrystals; is close to a direction parallel to a 2-fold axis. It turns out that the Yb content in the initial melt limited within 15-16 at.% is a critical factor determining the formation of single-grain quasicrystal. Based on the experimental result, the mechanism of the growth of single-grain quasicrystal and formation of intermediate zone between quasicrystal and approximant phases are discussed. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Dense quasicrystalline tilings by squares and equilateral triangles
Authors:
O'Keeffe, M; Treacy, MMJ Author Full Names: O'Keeffe, Michael; Treacy, Michael M. J.
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 66: 5-9 Part 1 JAN 2010
Abstract:
Dense square-symmetry tilings of the plane by equilateral triangles and squares are described. Repeated substitution of a vertex of a tiling by groups of vertices leads asymptotically to a limiting density that is independent of the starting pattern and to a family of quasicrystalline patterns with 12-fold symmetry. Diffraction patterns were computed by treating the vertices as point scatterers. As the number of substitutions increases, and as the unit-cell size increases, the diffraction patterns from a single unit cell develop a near-perfect 12-fold symmetry. In addition, the low-intensity background scattering in the diffraction patterns exhibits fractal-like self-similar properties, with motifs of local intensity recursively decorating the more intense features as the number of substitutions progresses.

M.D.

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