Special Interest Group on Aperiodic Crystals

Update: 31-Dec-2009
Title:: Effect of the "negative chemical" pressure on the temperatures of phase transitions in the TlInS2 layered crystal
Authors:: Seyidov, MHY; Suleymanov, RA; Salehli, F Author Full Names: Seyidov, M. - H. Yu.; Suleymanov, R. A.; Salehli, F.
Source:: PHYSICS OF THE SOLID STATE 51 (12): 2513-2519 DEC 2009
Abstract:: The temperature dependences of the permittivity of TlInS2(1 -x)Se2x solid solutions have been experimentally investigated in the temperature range including the points of structural phase transitions in the solid solutions. It has been established that the isovalent substitution of selenium for sulfur in the anion sublattice of the TlInS2(1 - x)Se2x solid solutions shifts the phase transition temperatures T (i) and T (c) toward the low-temperature range with a simultaneous decrease in the temperature interval of the existence of the incommensurate phase. The T-x phase diagram is constructed for the solid solutions under study and the coordinates are determined for a critical point (of the Lifshitz type) at which the lines T (i) (x) and T (c) (x) converge in the phase diagram. The pattern of the T-x phase diagram for the TlInS2(1 - x)Se2x solid solutions has been analyzed within the phenomenological model of a virtual crystal.
Update: 24-Dec-2009
Title:: Hydriding of Ti45Zr38Ni17-xFex nanocompounds
Authors:: Zywczak, A; Shinya, D; Gondek, L; Takasaki, A; Figiel, H Author Full Names: Zywczak, A.; Shinya, Daigo; Gondek, L.; Takasaki, Akito; Figiel, H.
Source:: SOLID STATE COMMUNICATIONS 150 (1-2): 1-4 JAN 2010
Abstract:: Ti-based quasicrystals belong to the second largest group of the stable quasicrystals, showing attractive properties as hydrogen storage materials. The Ti45Zr38Ni17 intermetallic compound forms an icosahedral (i-phase) structure, in which Ti and Zr atoms possess very good chemical affinity for hydrogen absorption. We modified the Ti45Zr38Ni17 compounds by substituting 3d metals (iron) for Ni to obtain amorphous phase. The samples were produced by mechanical alloying. The 3d metal atoms are located in the same positions as nickel. The structural characterization was made by means of XRD measurements. Thermodynamic properties were studied by differential scanning calorimetry (DSC) and thermal desorption spectroscopy (TDS). The obtained amorphous phases Ti45Zr38Ni(9,13)Fe(8,4) transform to the i-phase at the similar temperature range as Ti45Zr38Ni17. The final concentration of absorbed hydrogen depends on the amount of Fe. When increasing the amount of iron, the hydrogen release temperature becomes lower. After hydriding, the samples decompose into simple metal hydrides. (C) 2009 Elsevier Ltd. All rights reserved.
Title:: MODULATED MAGNETIC STATE OF A NONUNIFORMLY STRAINED IRON BORATE SINGLE CRYSTAL INDUCED BY A MAGNETIC FIELD
Authors:: Boidedaev, SR; Sokolov, BY Author Full Names: Boidedaev, S. R.; Sokolov, B. Yu.
Source:: RUSSIAN PHYSICS JOURNAL 52 (7): 759-762 JUL 2009
Abstract:: A remarkable feature of technical magnetization of a nonuniformly strained iron borate (FeBO3) crystal is long-period spatial modulation of the magnetic order parameter for this weak ferromagnet observed in external magnetic field H-1 <= H <= H-2 [1]. Investigations performed in [1] have demonstrated that the modulated magnetic structure (MMS) of nonuniformly strained FeBO3 arises when the vector. is oriented near a certain reference crystal direction of the easy magnetization (basal) crystal plane. During magnetization in this direction, rotation of the ferromagnetism vector m (or of the antiferromagnetism vector l perpendicular to m by definition) in the basal plane occurs somewhat specifically: after the termination of displacements of the domain boundaries, the single domain structure is first formed in the crystal, and the local vectors m appear oriented along the easy magnetization direction (the uniform low-field phase); then at H = H-1! , the magnetic structure of the crystal changes from the uniform to spatially modulated structure stable for H-1 <= H <= H-2 (the sinusoidal phase); then at H = H-2, the crystal passes once again to the uniform magnetic state with m parallel to H (the uniform high-field phase). The sinusoidal phase has the form of a static transverse spin wave linearly polarized in the basal plane in which the azimuth of the local vector m oscillates about the average magnetization direction. Since the MMS is not observed in FeBO3 without mechanical stresses, the specific feature of magnetization of the examined crystal established in [1] was attributed to the occurrence in its basal plane of additional spatially nonuniform (random) magnetic anisotropy caused by local deformations of the crystal lattice at mechanical stresses. According to models of crystal transition from the uniform to modulated magnetic state suggested in [1], the spatial orientation of the vector m (l) in the sinusoidal magnetic phase is determined by competition between the orienting action of the exchange forces on the local sublattice magnetic moments and the disorienting action of the nonuniform magnetic anisotropy forces. Experimental investigations performed in [1] demonstrated that the MMS was observed at temperatures. T < T-s approximate to 140 K; in the examined temperature interval (90 <= T <= 140 K), the spatial MMS period D remained virtually independent of., but significantly decreased with increasing.. In this case, the direction along which modulation of the azimuth of the vector m (l) is observed is independent of. and.; the amplitude of deviation of the local vector m from the average crystal magnetization direction decreases with increasing. and/or.; the field strengths at which the MMS is observed Delta H = (H-2 - H-1) -> 0 when T -> T-s; transitions low-field uniform phase <-> sinusoidal phase <-> high-field uniform phase are the first-order magnetic phase transitions. The present work analyzes the above-listed main properties and conditions of existence of the MMS in a nonuniformly strained FeBO3 crystal using the model suggested in [1].
Update: 17-Dec-2009
Title:: Origin of the long-wavelength magnetic modulation in Ca3Co2O6
Authors:: Chapon, LC Author Full Names: Chapon, L. C.
Source:: PHYSICAL REVIEW B 80 (17): Art. No. 172405 NOV 2009
Abstract:: The origin of the long-wavelength incommensurate magnetic structure of Ca3Co2O6 is discussed considering possible interchains super-superexchange paths. The experimental value of the propagation vector k=(0,0,Delta) with Delta>1 can be reproduced only if one considers the next-nearest super-superexchange interaction. A spin-dimer analysis using the extended Huckel tight-binding method confirms that, despite longer interatomic Co-Co distances, the latter interaction is indeed much stronger. The stability of the observed structure with respect to certain commensurate states is discussed.
Title:: Magnetic and electronic properties of Eu1-xSrxMnO3 (0.3 < x < 0.7) single crystals
Authors:: Tomioka, Y; Kumai, R; Ito, T; Tokura, Y Author Full Names: Tomioka, Y.; Kumai, R.; Ito, T.; Tokura, Y.
Source:: PHYSICAL REVIEW B 80 (17): Art. No. 174414 NOV 2009
Abstract:: Among versatile perovskite manganites showing colossal magnetoresistance (CMR), Eu1-xSrxMnO3 around x similar to 0.4 shows the ferromagnetic metal with the lowest transition temperature (similar to 40 K) due to the narrowest one-electron bandwidth and hence is readily subject to the drastic phase changes with variations in temperature, magnetic field, and hole doping (x). We have investigated the variation in the electronic state with x with use of single crystals. As x increases, the ferromagnetic metal at 0.38 < x < 0.47 changes to a spin-glasslike insulator at 0.48 < x < 0.5, the layered antiferromagnetic (A-type) state at 0.51 < x < 0.6, and the chained antiferromagnetic (C-type) state at 0.6 < x, respectively. Due to the increased disorder upon alloying of Eu/Sr, the charge/orbital ordering with the modulation vector (0, q, 0) with q=1/2 in the orthorhombic Pbnm setting (a(0)similar to b(0)similar to c(0)/root 2 similar to root 2a(p), a(p) being the lattice parameter of the pseudocubic lattice) cannot be formed in a long range but remains short ranged. In the vicinity of x=0.5, an application of an external magnetic field removes such short-range charge/orbital ordering (q=1/2) to cause an insulator to metal transition or CMR. In a broad range of x (0.55 < x < 0.59), the critical temperature for the layered antiferromagnetic state is relatively lowered and alternatively the charge/orbital ordering with q similar to 1/3 becomes to be visible. It has also been found that the modulation is temperature dependent; commensurate with q similar to 1/3 upon the transition while incommensurate with q>1/3 at low temperatures.
Title:: Transition from spin-density-wave to layered antiferromagnetic state induced by hydrogen as a test for the origin of spin-density waves in chromium
Authors:: Uzdin, VM; Zabel, H; Remhof, A; Hjorvarsson, B Author Full Names: Uzdin, V. M.; Zabel, H.; Remhof, A.; Hjorvarsson, B.
Source:: PHYSICAL REVIEW B 80 (17): Art. No. 174418 NOV 2009
Abstract:: Neutron scattering experiments of Cr/V(001) superlattices are discussed, which show that the incommensurate spin-density-wave (SDW) in thick Cr layers becomes suppressed when the V spacer layers are loaded with hydrogen. The hydrogen loading triggers a transition from the incommensurate SDW state to a commensurate antiferromagnetic state. Model Hamiltonian calculations are presented, which show that this transition is not connected with the nesting property of the Cr Fermi surface. Instead, the transition is a manifestation of the antiferromagnetic ground state of Cr, which is separated from the incommensurate SDW state by an energy barrier. Hydrogen is identified as an effective trigger for reducing the activation barrier, enabling the system to relax to the ground state.
Title:: Mutual enhancement of magnetism and Fulde-Ferrell-Larkin-Ovchinnikov superconductivity in CeCoIn5
Authors:: Mierzejewski, M; Ptok, A; Maska, MM Author Full Names: Mierzejewski, Marcin; Ptok, Andrzej; Maska, Maciej M.
Source:: PHYSICAL REVIEW B 80 (17): Art. No. 174525 NOV 2009
Abstract:: Recent experiments on CeCoIn5 suggest an unusual interplay between superconducting and magnetic orders that gives rise to a multicomponent (magnetosuperconducting) phase. We demonstrate that characteristics of CeCoIn5 make this system particularly well suited for the onset of such a phase. Based on general considerations, we show that superconductivity with nonzero Cooper-pair momentum may lead to an enhancement of the spin-spin response function and, simultaneously, incommensurate spin-density wave may enhance the Cooper-pair susceptibility.
Title:: Incommensurate spin correlation driven by frustration in BiCu2PO6
Authors:: Mentre, O; Janod, E; Rabu, P; Hennion, M; Leclercq-Hugeux, F; Kang, J; Lee, C; Whangbo, MH; Petit, S Author Full Names: Mentre, O.; Janod, E.; Rabu, P.; Hennion, M.; Leclercq-Hugeux, F.; Kang, J.; Lee, C.; Whangbo, M. -H.; Petit, S.
Source:: PHYSICAL REVIEW B 80 (18): Art. No. 180413 NOV 2009
Abstract:: The magnetic properties of BiCu2PO6 have been analyzed by means of magnetic-susceptibility and inelastic neutron-scattering measurements on powder samples by evaluating the spin-exchange interactions on the basis of density-functional calculations and by simulating the inelastic neutron scattering in terms of spin-exchange parameters. BiCu2PO6 exhibits magnetic properties described by the two-leg spin ladder with strong spin frustration along each leg chain and has a gapped quantum singlet ground state with excited magnetic states, showing an incommensurate dispersion arising from frustration.
Title:: Basic Co-rich decagonal Al-Co-Ni: Average structure
Authors:: Strutz, A; Yamamoto, A; Steurer, W Author Full Names: Strutz, Angelica; Yamamoto, Akiji; Steurer, Walter
Source:: PHYSICAL REVIEW B 80 (18): Art. No. 184102 NOV 2009
Abstract:: The two-layer average structure of the high-temperature phase basic Co-rich decagonal Al72.5Co18.5Ni9 was determined based on single-crystal x-ray diffraction data. The five-dimensional (5D) structure model was refined in the noncentrosymmetric 5D space group P10m2 (112 parameters, wR=0.123 and R=0.156 for 957 reflections). The close relationship of the model structure with that of W-Al-Co-Ni, a << 3/2,2/1 >> approximant, is shown.
Title:: Magnetism in CeFeAsO1-xFx and LaFeAsO1-xFx from first principles
Authors:: Sharma, S; Shallcross, S; Dewhurst, JK; Sanna, A; Bersier, C; Massidda, S; Gross, EKU Author Full Names: Sharma, S.; Shallcross, S.; Dewhurst, J. K.; Sanna, A.; Bersier, C.; Massidda, S.; Gross, E. K. U.
Source:: PHYSICAL REVIEW B 80 (18): Art. No. 184502 NOV 2009
Abstract:: Using state-of-the-art first-principles calculations we study the magnetic behavior of CeOFeAs. We find the Ce layer moments oriented perpendicular to those of the Fe layers. An analysis of incommensurate magnetic structures reveals that the Ce-Ce magnetic coupling is rather weak with, however, a strong Fe-Fe and Fe-Ce coupling. Comparison of the origin of the tetragonal to orthorhombic structural distortion in CeOFeAs and LaOFeAs shows marked differences; in CeOFeAs the distortion is stabilized by a lowering of spectral weight at the Fermi level, while in LaOFeAs by increase in Fe spin moment. Finally, we investigate the impact of electron doping upon CeOFeAs and LaOFeAs and show that (a) while in CeOFeAs the ground-state Fe moment remains largely unchanged by doping, the stability of magnetic order goes to zero at a doping that corresponds well to the vanishing of the Neacuteel temperature and, (b) in contrast the LaOFeAs system remains magnetic wit! h a slowly vanishing moment as a function of doping.
Title:: Optimizing the thermoelectric efficiency of icosahedral quasicrystals and related complex alloys
Authors:: Macia, E Author Full Names: Macia, Enrique
Source:: PHYSICAL REVIEW B 80 (20): Art. No. 205103 NOV 2009
Abstract:: In this work we analyze the potential role of quasicrystals and related alloys in thermoelectric material research. Relatively large figure of merit values are expected for those samples exhibiting two properly located narrow features in the density of states close to the Fermi level. It is expected that optimized quasicrystals will perform better at relatively low temperatures, whereas the ZT curve of complex metallic alloys reaches its maximum at high temperatures. Among state-of-the-art quasicrystals most promising samples for thermoelectric applications are found in the AlPd (Mn,Re) system. Quasicrystalline and related approximants in the ScMgCuGa and CaAuIn systems, synthesized on the basis of pseudogap tuning concepts, appear as promising candidates as well.
Title:: Disordered, quasicrystalline and crystalline phases of densely packed tetrahedra
Authors:: Haji-Akbari, A; Engel, M; Keys, AS; Zheng, XY; Petschek, RG; Palffy-Muhoray, P; Glotzer, SC Author Full Names: Haji-Akbari, Amir; Engel, Michael; Keys, Aaron S.; Zheng, Xiaoyu; Petschek, Rolfe G.; Palffy-Muhoray, Peter; Glotzer, Sharon C.
Source:: NATURE 462 (7274): 773-U91 DEC 10 2009
Abstract:: All hard, convex shapes are conjectured by Ulam to pack more densely than spheres(1), which have a maximum packing fraction of phi = pi/root 18 approximate to 0.7405. Simple lattice packings of many shapes easily surpass this packing fraction(2,3). For regular tetrahedra, this conjecture was shown to be true only very recently; an ordered arrangement was obtained via geometric construction with phi = 0.7786 (ref. 4), which was subsequently compressed numerically to phi = 0.7820 (ref. 5), while compressing with different initial conditions led to phi = 0.8230 ( ref. 6). Here we show that tetrahedra pack even more densely, and in a completely unexpected way. Following a conceptually different approach, using thermodynamic computer simulations that allow the system to evolve naturally towards high-density states, we observe that a fluid of hard tetrahedra undergoes a first-order phase transition to a dodecagonal quasicrystal (7-10), which can be compressed to a packing fraction of phi = 0.8324. By compressing a crystalline approximant of the quasicrystal, the highest packing fraction we obtain is phi = 0.8503. If quasicrystal formation is suppressed, the system remains disordered, jams and compresses to phi = 0.7858. Jamming and crystallization are both preceded by an entropy-driven transition from a simple fluid of independent tetrahedra to a complex fluid characterized by tetrahedra arranged in densely packed local motifs of pentagonal dipyramids that form a percolating network at the transition. The quasicrystal that we report represents the first example of a quasicrystal formed from hard or non-spherical particles. Our results demonstrate that particle shape and entropy can produce highly complex, ordered structures.
Title:: Effects of the fourth component and undercooling on morphology of primary Mg-Zn-Y icosahedral quasicrystal phase under normal casting conditions
Authors:: Wang, ZF; Zhao, WM; Hur, BY; Huang, CY; Yu, CQ Author Full Names: Wang Zhifeng; Zhao Weimin; Hur, Bo-Young; Huang Chunying; Yu Chengquan
Source:: CHINA FOUNDRY 6 (4): 293-299 NOV 2009
Abstract:: The paper presents some results of the investigation on effects of the fourth component (Ti, C, Sb or Cu) and undercooling on the morphology, size and forming process of primary Mg-Zn-Y icosahedral quasicrystal phase (I-phase) under normal casting conditions. The result shows that the addition of certain amount of fourth component can transform I-phase morphology from petal-like to spherical. However, I-phase will grow up to petal-like if superfluous addition of the fourth component applied. It is also found that the solidified morphology of I-phase depends on the stability of spherical I-phase during the subsequent growth, and critical radius of maintaining the spherical I-phase interface relatively stable. Further, mini-sized spherical I-phase can be produced with high content of the fourth component by undercooling. Such findings are benefical for industrializing Mg-based quasicrystals.
Update: 11-Dec-2009
Title:: Influence of Boron Additions on Dissipative Properties of Quasicrystalline Al-Cu-Fe Coatings
Authors:: Ustinov, AI; Polishchuk, SS; Telychko, VA; Melnychenko, TV Author Full Names: Ustinov, A. I.; Polishchuk, S. S.; Telychko, V. A.; Melnychenko, T. V.
Source:: METALLOFIZIKA I NOVEISHIE TEKHNOLOGII 31 (6): 847-854 JUN 2009
Abstract:: Influence of boron on mechanical and dissipative properties of quasicrystalline Al-Cu-Fe coatings is studied. As shown, the hardness of coatings based on quasicrystalline Al-Cu-Fe phase under alloying with boron remains practically unchanged, while their fracture toughness slightly increases. At the same time, damping capacity of nanoquasicrystalline coating Al-Cu-Fe-B is found to be essentially lower as compared with that of similar coating without boron. Possible mechanisms of the change in dissipative properties are discussed.
Title:: The commensurate modulated structure of the metastable state in spin crossover complex [Fe(abpt)(2)(NCS)(2)]
Authors:: Sheu, CF; Chen, SM; Wang, SC; Lee, GH; Liu, YH; Wang, Y Author Full Names: Sheu, Chou-Fu; Chen, Szu-Miao; Wang, Shih-Chi; Lee, Gene-Hsiang; Liu, Yi-Hung; Wang, Yu
Source:: CHEMICAL COMMUNICATIONS (48): 7512-7514 2009
Abstract:: Two new polymorphs (C and D) of [t-Fe(abpt)(2)(NCS)(2)] are characterized, a commensurate modulated structure with the c axis tripled in the thermally quenched metastable high spin state at 25 K is found in polymorph C.
Title:: Superplastic Behavior in Mg-Zn-Y Alloy with Dispersed Quasicrystal Phase Particles
Authors:: Somekawa, H; Singh, A; Mukai, T Author Full Names: Somekawa, Hidetoshi; Singh, Alok; Mukai, Toshiji
Source:: ADVANCED ENGINEERING MATERIALS 11 (10): 782-787 OCT 2009
Update: 4-Dec-2009
Title:: Influence of polytypism on structural phase transformations in TlGaSe2 crystals
Authors:: Borovoi, NA; Gololobov, YP; Isaenko, GL; Stepanishchev, NB Author Full Names: Borovoi, N. A.; Gololobov, Yu. P.; Isaenko, G. L.; Stepanishchev, N. B.
Source:: PHYSICS OF THE SOLID STATE 51 (11): 2367-2370 NOV 2009
Abstract:: The polytypism is found to have a significant influence on the structural transformation of the crystal lattice of the TlGaSe2 ferroelectric with variations in temperature. In the 2C-polytype, unlike the C-polytype, a first-order structural phase transition, which leads to a change in the translational symmetry along the C axis, is not observed in the temperature range T = 90-300 K and a second-order phase transition due to the formation of an incommensurate phase occurs at a higher temperature.
Title:: Crossover Induced by Spin-Density-Wave Interference in the Coherence of Singlet Electron Pairs in Cr
Authors:: Robinson, JWA; Halasz, GB; Blamire, MG Author Full Names: Robinson, J. W. A.; Halasz, Gabor B.; Blamire, M. G.
Source:: PHYSICAL REVIEW LETTERS 103 (20): Art. No. 207002 NOV 13 2009
Abstract:: To study the interaction of s-wave superconductivity with spin-density waves (SDWs), we have measured a series of Nb/Cr/Nb Josephson junctions and determined the coherence length xi describing the decay of the critical current with Cr thickness, L. We observe a crossover in xi from approximately 14 nm to 4 nm as L increases to 10 nm, which is consistent with a transition from commensurate to incommensurate SDWs expected for this thickness range.
Title:: Ferroelastic crystals and their nonlinear elastic properties observed in frequency range from gigahertz to milihertz
Authors:: Wiesner, M Author Full Names: Wiesner, Maciej
Source:: PHASE TRANSITIONS 82 (10): 699-754 2009
Abstract:: The experiments reported in this article have been performed to unify the results of earlier and recent determinations of parameters describing the elastic properties of Rb4LiH3(SO4)4, LiCsSO4 (LCS) and KH2PO4 crystals measured by different experimental methods. The above crystals undergo a second-order phase transition, incommensurate phase transition (PT) and a first-order but close to second-order phase transition, respectively. To investigate the elastic properties of the crystals in the frequency range from 10-1 to 1010 Hz, five experimental methods were applied: dynamic mechanical analysis, piezoelectric resonance, composite oscillator bar, ultrasonic wave propagation and Brillouin light scattering. The results of the experiments allowed identification of the processes contributing to the elastic response of the crystals investigated. Moreover, for the LCS crystal a model of the incommensurate PT was presented.
Title:: Quasicrystalline phase formation in the conventionally solidified Al-Cu-Fe system
Authors:: Gogebakan, M; Avar, B; Uzun, O Author Full Names: Gogebakan, M.; Avar, B.; Uzun, O.
Source:: MATERIALS SCIENCE-POLAND 27 (3): 919-926 2009
Abstract:: Structural characteristics and thermal behaviour of the conventionally solidified Al-Cu-Fe alloys with nominal compositions of Al70Cu20Fe10, Al65Cu20Fe15 and Al63Cu25Fe12 were investigated by X-ray diffraction, scanning electron microscopy, and differential thermal analysis techniques. Results show that a single quasicrystalline phase forms in a conventionally solidified Al65Cu20Fe15 alloy, being thermodynamically stable without phase transition up to the melting point. A cubic AlFe(Cu) solid solution, identified as beta phase, and a cubic AlCu(Fe) solid solution, identified as tau phase, were observed with quasicrystalline phase for Al63Cu25Fe12 alloy. Conventional solidification of Al70Cu20Fe10 alloy does not result in quasicrystalline phase formation. However, the formation of quasicrystalline phase in conventionally solidified Al70Cu20Fe10 alloy was observed after additional annealing at elevated temperature. SEM micrographs for Al70Cu20Fe10 and Al63Cu25Fe12 alloys after annealing at 700 degrees C for 4 h revealed the formation of pentagonal dodecahedrons in the quasicrystalline phase, with an edge size of about 30 mu m.
Title:: Monte-Carlo investigation of an anisotropic Ising model
Authors:: Murtazaev, AK; Ibaev, ZG Author Full Names: Murtazaev, A. K.; Ibaev, Zh. G.
Source:: LOW TEMPERATURE PHYSICS 35 (10): 792-796 OCT 2009
Abstract:: The Monte Carlo method is used to study long-period modulated structures in an anisotropic Ising model with competing interactions (ANNNI model). The character, particularities, and dependence of the modulated structures on the temperature and ratio of the exchange interaction constants between the nearest and next-to-nearest neighbors are determined. The phase diagram is constructed. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3253402]
Title:: Lattice Distortion Coupled with Magnetic Ordering in a Triangular Lattice Antiferromagnet CuCrO2
Authors:: Kimura, K; Otani, T; Nakamura, H; Wakabayashi, Y; Kimura, T Author Full Names: Kimura, Kenta; Otani, Tsuyoshi; Nakamura, Hiroyuki; Wakabayashi, Yusuke; Kimura, Tsuyoshi
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (11): Art. No. 113710 NOV 2009
Abstract:: We investigated magnetostrictive properties of a triangular lattice antiferromagnet CuCrO2 showing an incommensurate proper-screw spin order by means of x-ray diffraction and strain gauge measurements. A deformation of the triangular lattice plane leading to a lowered crystallographic symmetry was found upon the magnetic ordering, which demonstrates a strong spin-lattice coupling in this system. The resultant multiple structural domains can be successfully arranged by magnetic field cooling procedures. We discuss the relationship between the lattice distortion and incommensurability in CuCrO2.
Title:: Renormalization of Commensurate Magnetic Peak in Ni-Doped La1.85Sr0.15CuO4
Authors:: Matsuura, M; Kofu, M; Kimura, H; Hirota, K Author Full Names: Matsuura, Masato; Kofu, Maiko; Kimura, Hiroyuki; Hirota, Kazuma
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (11): Art. No. 114703 NOV 2009
Abstract:: We have studied magnetic excitations in impurity-doped La(1.85)Sr(0.15)Cu(1-y)A(y)O(4) (A = Ni or Zn) by neutron scattering. The dispersion for Zn:y = 0.017 is similar to that for the impurity-free sample: incommensurate peaks with incommensurability delta = 0.12 +/- 0.01 (rlu) do not change their positions up to 21 meV. On the other hand, for Ni:y = 0.029, two incommensurate peaks observed at low energies suddenly change into a single broad commensurate peak at E-cross = 15 meV. Compared with that for the impurity-free sample with a similar Sr concentration of x = 0.16, E-cross for Ni:y = 0.029 is decreased by nearly the same factor as the reduction in T-c. This is very similar to the shift of resonance energy (E-res) in Ni-doped YBa2Cu3O7. These common impurity effects on the shifts of E-cross and E-res suggest the same magnetic origin of the resonance peak in YBa2Cu3O6+x and that of the crossing point of upward and downward dispersions in La2-xSrxCuO4. We propose that the sudden change in the dispersions is better described by a crossover from incommensurate spin fluctuations to a gapped spin wave rather than an hourglass-like dispersion.
Title:: Antiferromagnetic Order and pi-Triplet Pairing in the Fulde-Ferrell-Larkin-Ovchinnikov State
Authors:: Yanase, Y; Sigrist, M Author Full Names: Yanase, Youichi; Sigrist, Manfred
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (11): Art. No. 114715 NOV 2009
Abstract:: The anti ferromagnetic Fulde-Ferrell-Larkin-Ovchinnikov (AFM-FFLO) state of coexisting d-wave FFLO superconductivity and incommensurate AFM order is studied on the basis of Bogoliubov-de Gennes (BdG) equations. We show that the incommensurate AFM order is stabilized in the FFLO state by the appearance of the Andreev bound state localized around the zeros of the FFLO order parameter. The AFM-FFLO state is further enhanced by the induced pi-triplet superconductivity (pair density wave). The AFM order occurs in the FFLO state even when it is neither stable in the normal state nor in the BCS state. The order parameters of the AFM order, d-wave superconductivity, and pi-triplet pairing are investigated by focusing on their spatial structures. Roles of the spin fluctuations beyond the BdG equations are discussed. Their relevance to the high-field superconducting phase of CeCoIn5 is discussed.
Title:: Atomic dynamics of a d-AlNiFe decagonal quasicrystal
Authors:: Parshin, PP; Zemlyanov, MG; Panova, GK; Shikov, AA; Brand, RA; Grushko, B Author Full Names: Parshin, P. P.; Zemlyanov, M. G.; Panova, G. Kh.; Shikov, A. A.; Brand, R. A.; Grushko, B.
Source:: JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 109 (4): 645-651 OCT 2009
Abstract:: The atomic dynamics of an Al71.3Ni24Fe4.7 decagonal quasicrystal has been investigated using the isotopic contrast method for inelastic neutron scattering. The partial vibrational spectra of the Ni, Fe, and Al atoms and the spectrum of the thermal vibrations of the alloy have been reconstructed directly from the experimental data without any model assumptions. The cutoff energies and the positions of the main features of the spectra have been determined. It has been revealed that the average binding energy of the nickel atoms in the quasicrystal under investigation is lower than that of the iron atoms and the vibrational spectrum of the aluminum atoms is noticeably harder than the spectrum of the pure metal. The results obtained for the d-AlNiFe decagonal quasicrystal have been compared with the previously published data for an i-AlCuFe icosahedral quasicrystal.
Update: 26-Nov-2009
Title:: Long-period states of a crystal finite-size-particle system
Authors:: Dmitriev, SV; Potekaev, AI; Samsonov, AV Author Full Names: Dmitriev, S. V.; Potekaev, A. I.; Samsonov, A. V.
Source:: RUSSIAN PHYSICS JOURNAL 52 (6): 622-639 JUN 2009
Abstract:: A one-dimensional model is proposed, which ensures description of origination and main properties of longperiod and incommensurate phases of crystal having complex structure and consists of comparatively rigid "atomic clusters". In the case where reciprocal rotations of theses clusters are considerably large, not only translational but also rotational degrees of freedom have to be taken into account for the clusters. It is consideration of the rotational degrees of freedom which might provide for formation of long-period states and development of a number of physical effects, such as a variety of soliton solutions (of domain walls) and their non-trivial dynamics.
Title:: High-resolution electron microscopy for incommensurate structure of KxRhO2 crystal
Authors:: Yubuta, K; Shibasaki, S; Terasaki, I; Kajitani, T Author Full Names: Yubuta, Kunio; Shibasaki, Soichiro; Terasaki, Ichiro; Kajitani, Tsuyoshi
Source:: PHILOSOPHICAL MAGAZINE 89 (31): 2813-2822 2009
Abstract:: An incommensurate, (3 + 2)- dimensional structure is locally observed in a K0.49RhO2 crystal synthesized by the flux growth method. The averaged potassium to rhodium ratio of the grown crystals was determined as 0.49 using an electron probe microanalyzer operated in the wave dispersive spectroscopy mode. The potassium content of the incommensurate phase was determined as 0.25 by the transmission electron microscopy-energy dispersive spectroscopy method. Satellite reflections of an incommensurate phase having two modulation vectors, q(1)* = 0.15a(o)* + 0.21b(o)* and q(2)* = -0.21a(o)* + 0.36b(o)* (a(o) is the unit cell for a gamma-NaxCoO2-type structure), are indexed successfully. High-resolution electron microscopy (HREM) images show dark streaks running parallel in the a-b plane. The separations and directions of the dark streaks have a close relationship between the q-vector of satellite spots. A HREM image taken with the electron beam parallel to [100] direction shows planer clusters between CdI2-type RhO2 layers. These clusters correspond to the intercalated potassium ions.
Title:: Plastic analysis of crack problems in three-dimensional icosahedral quasicrystalline material
Authors:: Li, W; Fan, TY; Wu, YL Author Full Names: Li, Wu; Fan, Tian You; Wu, Yun Long
Source:: PHILOSOPHICAL MAGAZINE 89 (31): 2823-2831 2009
Abstract:: Due to their complexity, the basic plastic properties of all quasicrystalline materials are essentially unknown [M. Feuerbacher, C. Thomas, K. Urban, Plastic behaviour of quasicrystalline materials, in Quasicrystals: Structure and Physical Properties, H.R. Trebin, ed., Wiley/VCH, Berlin, 2003]. Plastic deformation of cracks in icosahedral quasicrystals have been analyzed in a strict and systematic form and the crack tip opening displacement (CTOD) and size of the plastic zone around the crack tip was determined exactly. CTOD is suggested as a parameter of plastic fracture for quasicrystalline materials. The present work may also provide a novel methodology for plastic analysis of quasicrystals.
Title:: Octahedral tilt twinning and compositional modulation in NaLaMgWO6
Authors:: King, G; Garcia-Martin, S; Woodward, PM Author Full Names: King, Graham; Garcia-Martin, Susana; Woodward, Patrick M.
Source:: ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 676-683 Part 6 DEC 2009
Abstract:: A combination of selected-area electron diffraction (SAED), neutron powder diffraction (NPD) and high-resolution transmission electron microscopy (HRTEM) reveals a complex superstructure in the ordered perovskite NaLaMgWO6. Through indexing of SAED patterns the unit-cell dimensions are found to be 46.8 x 7.8 x 7.9 angstrom, which corresponds to a 12a(p) x 2a(p) x 2a(p) superstructure of the simple Pm (3) over barm perovskite unit cell. HRTEM images reveal the formation of an unmistakable stripe contrast that repeats with the same periodicity. Doubling of the b and c axes is brought about by a combination of layered ordering of Na and La, rock-salt ordering of Mg and W, and octahedral tilting. The a axis repeat distance results from a one-dimensional twinning of the octahedral tilts in combination with a compositional modulation. Modeling of the NPD pattern shows that the underlying tilt system is a(-)a(-)c(0) with tilt angles of similar to 8 degrees about the a and b axes. The octahedral tilt-twin boundaries run perpendicular to the a axis and are separated by 6a(p). Simulated HRTEM images show that octahedral tilt twinning alone cannot explain the stripes seen in the HRTEM images, rather a compositional modulation involving the A-site cations is necessary to explain the experimental images.
Update: 19-Nov-2009
Title:: A One-Dimensional Metal Embedded in Salt Matrices: Synthesis, Modulated Crystal Structures, Electrical Conductivity, and Chemical Bonding of (1)(infinity)[PdBi6][(Bi,Sn)(1-delta)Br5-delta,]
Authors:: Wahl, B; Kloo, L; Ruck, M Author Full Names: Wahl, Bernhard; Kloo, Lars; Ruck, Michael
Source:: ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE 635 (12): 1979-1985 2009
Abstract:: The metal-rich compounds (1)(infinity)[PdBi6][(Bi,Sn)(1-delta)Br5-delta,] with delta(1) = 2/13, delta(1)' = 5/26, or delta(2) = delta(2)' = 2/12 were synthesized from Bi2Pd, BiBr3, and Sn at 300 degrees C. The crystal structures contain intermetallic rods (1)(infinity)[Pd@Bi2/1Bi8/2](2.5+) embedded in salt-like matrices, which consist of groups of bromido-bismuthate(III)-stannate(II) octahedra [(Bi,Sn)(n)Br4n+2](m-) (n = 2, 3) and isolated Br- ions. Metrical incompatibilities of the two subsystems in the crystalline metal-salt hybrid result in non-stoichiometry of the salt pan associated with complex superstructures. The average structure is described in the orthorhombic space group Pmmm with a approximate to 408 pm, b approximate to 2263 pm, c approximate to 849 pm. It feigns statistical distribution of vacancies and orientational disorder of the concatenated octahedra. By choosing the modulation vectors q(i) = 2/ta* + 1/2b* + 1/2c* with t(1) = 13 or t(2) = 12, the additional weak reflections of the diffraction patterns are indexed. Ordered structure models are achieved in the [3+1]-dimensional superspace group Pmmm(alpha 1/21/2)000. Metallic conductivity along [100], i.e. the direction of the (1)(infinity)[Pd@Bi2/1Bi8/2](2.5+) rods, was determined for a single-crystal. One-dimensional band structure calculations reveal Bi p-bands crossing the Fermi level for formula charges higher than 2+. The electron localization indicator (ELI) indicates two-center Bi-Bi bonds as well as multi-center bonds inside the metallic part, whereas the bismuth l one-pairs point towards the non-conducting part of the structure.
Title:: Quasiparticles of Spatially Anisotropic Triangular Antiferromagnets in a Magnetic Field
Authors:: Kohno, M Author Full Names: Kohno, Masanori
Source:: PHYSICAL REVIEW LETTERS 103 (19): Art. No. 197203 NOV 6 2009
Abstract:: The spectral properties of the spin-1/2 Heisenberg antiferromagnet on an anisotropic triangular lattice in a magnetic field are investigated using a weak-interchain-coupling approach combined with exact solutions of a chain. Dominant modes induced by interchain interactions in a magnetic field behave as quasiparticles which show distinctive features such as anomalous incommensurate ordering and high-energy modes. In terms of them, various unusual features observed in the anisotropic triangular antiferromagnet Cs2CuCl4 in a magnetic field are quantitatively explained in a unified manner.
Title:: The uniaxially aperiodic structure of a thin Cu film on fivefold i-Al-Pd-Mn
Authors:: Pussi, K; Gierer, M; Diehl, RD Author Full Names: Pussi, K.; Gierer, M.; Diehl, R. D.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (47): Art. No. 474213 NOV 25 2009
Abstract:: A thin film of copper on the fivefold surface of Al-Pd-Mn forms a structure that is uniaxially commensurate with the aperiodic structure of the substrate. This structure has been analyzed using low-energy electron diffraction and is found to consist of a vicinal surface of a body-centered tetragonal (bct) (100) structure. This bct(100) structure has lattice parameters of a = 2.88 angstrom, b = 2.55 angstrom and c = 2.88 angstrom, with the vicinal surface making an angle alpha of 13.28 degrees relative to the a-b plane. This structure provides an explanation for the delayed ordering observed during the growth of the film. Simple conditions are derived for which the growth of ordered one-dimensionally quasiperiodic thin films on quasicrystals may be favorable. This finding is relevant to the use of quasicrystals as a means of matching interfaces in thin film systems.
Title:: Synthesis of the quasi-crystalline phase in Al63Cu25Fe12 powders prepared by mechanical alloying
Authors:: Avar, B; Gogebakan, M Author Full Names: Avar, B.; Gogebakan, M.
Source:: JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS 11 (10): 1460-1463 OCT 2009
Abstract:: This work investigated the quasicrystalline phase formation during heat treatment in the Al63Cu25Fe12 alloy prepared via mechanical alloying, starting from pure elemental powders. The mechanical alloying process was performed at a speed of 300 rpm for times up to 70 hours. The structural evolution of the mechanically alloyed Al63Cu25Fe12 powders at different stages of milling was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The present results showed that mechanical alloying of the Al63Cu25Fe12 alloy did not result in the quasicrystalline icosahedral phase (i-phase). The long time milling resulted in the formation of an AlFe(Cu) solid solution identified as the beta-phase. In order to examine the structural changes with annealing temperature, the mechanically alloyed powders were heat treated at 600, 700 and 800 degrees C for 4 hours under vacuum. However, the formation of a quasicrystalline phase in the Al63Cu25Fe12 alloy was observed after additional annealing at elevated temperature. In the present work, quasicrystalline phase formation in both the as-milled and heat-treated powders is discussed in detail.
Title:: Minerals as advanced materials
Authors:: Depmeier, W Author Full Names: Depmeier, W.
Source:: CRYSTAL RESEARCH AND TECHNOLOGY 44 (10): 1122-1130 Sp. Iss. SI OCT 2009
Abstract:: A resume is given on relationships between minerals and materials. It is shown that Nature has many advantages over technology which can be profitably exploited for finding new materials with useful properties. However, Nature has also inherent limitations. Therefore, it seems advisable to use the knowledge of minerals as a treasure which can be tapped for getting inspired on the way to finding new materials. Several examples are given, including those of zorite/ETS-4/ETS-10, boracites, zircon, kesterite, a natural quasicrystal, opals, ultramarine and mayenite.
Update: 13-Nov-2009
Title:: AlCoNi quasicrystal sphere growth experiment from a metallic solution
Authors:: Meisterernst, G; Bauer, B; Gille, P Author Full Names: Meisterernst, Goetz; Bauer, Birgitta; Gille, Peter
Source:: ZEITSCHRIFT FUR KRISTALLOGRAPHIE 224 (10): 471-477 2009
Abstract:: Crystal growth studies starting from spherical surfaces of single crystals can reveal morphological features that cannot be obtained in usual growth experiments. Especially, facets of a greater variety of crystallographic forms may occur that are otherwise hidden by the slowest growing faces which dominate the crystal's morphology. We did a sphere growth experiment with a decagonal Al72Co9Ni19 quasicrystal prepared from a large single-grain sample formerly grown using the Czochralski method from an off-stoichiometric melt. By heating the polished crystalline half-sphere to a temperature slightly higher than its own growth temperature a thin liquid layer of self-flux formed. A partial evaporation of Al being the solvent of this system caused re-crystallisation at the surface of the quasicrystalline sphere. After several times repeating this process at further increasing temperatures, tiny faces of four different crystallographic forms developed. By using an optical goniometer and electron scanning microscopy indexing of these facets was possible. With the only exception of the decagonal prism {10000} they had not been observed so far in contact to the melt. The results are discussed with respect to the inclined net plane concept established by Steurer and Cervellino [Acta Cryst. A57 (2001) 333-340]. The experimental approach is not specific to sphere growth studies of quasicrystals but can be applied to other high-temperature solution growth systems as well.
Title:: Atomic coexistence of superconductivity and incommensurate magnetic order in the pnictide Ba(Fe(1-x)Cox)(2)As-2
Authors:: Laplace, Y; Bobroff, J; Rullier-Albenque, F; Colson, D; Forget, A Author Full Names: Laplace, Y.; Bobroff, J.; Rullier-Albenque, F.; Colson, D.; Forget, A.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 140501 OCT 2009
Abstract:: As-75 nuclear magnetic resonance (NMR) and susceptiblity were measured in a Ba(Fe1-xCox)(2)As-2 single crystal for x=6%. NMR spectra and relaxation rates allow to show that all Fe sites experience an incommensurate magnetic ordering below T=31 K. Comparison with undoped compound allows to estimate a typical moment of 0.05 mu(B). Anisotropy of the NMR widths can be interpreted using a model of incommensurability with a wave vector (1/2-epsilon,0, l) with epsilon of the order of 0.04. Below T-C=21.8 K, a full volume superconductivity develops as shown by susceptibility and relaxation rate, and magnetic order remains unaffected, demonstrating coexistence of both states on each Fe site.
Title:: Coexistence of incommensurate magnetism and superconductivity in Fe(1+y)SexTe(1-x)
Authors:: Khasanov, R; Bendele, M; Amato, A; Babkevich, P; Boothroyd, AT; Cervellino, A; Conder, K; Gvasaliya, SN; Keller, H; Klauss, HH; Luetkens, H; Pomjakushin, V; Pomjakushina, E; Roessli, B Author Full Names: Khasanov, R.; Bendele, M.; Amato, A.; Babkevich, P.; Boothroyd, A. T.; Cervellino, A.; Conder, K.; Gvasaliya, S. N.; Keller, H.; Klauss, H. -H.; Luetkens, H.; Pomjakushin, V.; Pomjakushina, E.; Roessli, B.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 140511 OCT 2009
Abstract:: We have studied the superconducting and magnetic properties of Fe1+ySexTe1-x single crystals (0 <= x <= 0.5) by magnetic susceptibility, muon-spin rotation, and neutron diffraction. We find three regimes of behavior: (i) commensurate magnetic order for x less than or similar to 0.1, (ii) bulk superconductivity for x similar to 0.5, and (iii) a range x approximate to 0.25-0.45 in which superconductivity coexists with incommensurate magnetic order. The results are qualitatively consistent with two-band mean-field models in which itinerant magnetism and extended s-wave superconductivity are competing order parameters.
Title:: Transition from turbulent to nearly laminar vortex flow in superconductors with periodic pinning
Authors:: Gutierrez, J; Silhanek, AV; Van de Vondel, J; Gillijns, W; Moshchalkov, VV Author Full Names: Gutierrez, J.; Silhanek, A. V.; Van de Vondel, J.; Gillijns, W.; Moshchalkov, V. V.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 140514 OCT 2009
Abstract:: We revisit the vortex dynamics in Al thin films containing an artificial periodic array of antidots by means of electrical transport measurements. We clearly identify a turbulent to laminarlike vortex flow transition which manifests itself as a negative differential resistivity. This transition is accompanied by a strong irreversibility in the voltage-current characteristics. The dynamical phase diagrams obtained as a function of commensurability, temperature, and driving force are in good agreement with the early predictions by Reichhardt et al. [Phys. Rev. Lett. 78, 2648 (1997)] based on molecular dynamic simulations.
Title:: Lattice dynamics and external magnetic-field effects in Ni-Fe-Ga alloys
Authors:: Perez-Landazabal, JI; Recarte, V; Sanchez-Alarcos, V; Rodriguez-Velamazan, JA; Jimenez-Ruiz, M; Link, P; Cesari, E; Chumlyakov, YI Author Full Names: Perez-Landazabal, J. I.; Recarte, V.; Sanchez-Alarcos, V.; Rodriguez-Velamazan, J. A.; Jimenez-Ruiz, M.; Link, P.; Cesari, E.; Chumlyakov, Y. I.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 144301 OCT 2009
Abstract:: Precursor phenomena were investigated in a Ni-Fe-Ga alloy close to the stoichiometric Heusler composition Ni2FeGa. In particular, the phonon-dispersion curves, the diffuse scattering and the magnetic properties of a single crystalline Ni51.5Fe21.5Ga27 alloy were measured as a function of temperature. The TA(2) branch along the [110] direction of the L2(1) phase shows a significant phonon softening around xi = 0.35 resulting in a marked dip which becomes more pronounced as the temperature decreases. Diffuse neutron-scattering measurements performed along [(xi) over bar xi 0] direction around Bragg reflections also reveal the presence of small satellite peaks at xi = 0.33 whose intensity increases on approaching the martensitic transformation temperature. Both elastic and inelastic-scattering anomalies confirm the occurrence of premartensitic phenomena in Ni-Fe-Ga alloys. The influence of an external magnetic field (6 T) on the anomalous phonon is shown to be negli! gible and just a small shift of the transformation temperature takes place because of the magnetic field.
Title:: Thermal entanglement of spin chains with quantum critical behavior
Authors:: Zvyagin, AA Author Full Names: Zvyagin, A. A.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 144408 OCT 2009
Abstract:: Results for the characteristics of the macroscopic thermal entanglement for integrable spin-1/2 antiferro-magnetic chain models with multispin interactions in the thermodynamic limit are presented. Such interactions cause quantum-phase transitions to incommensurate phases with partial spontaneous magnetization. We have derived exact equations, which determine the thermal and magnetic field behavior of the concurrence of spin chains. The analysis of these equations shows that there exists a critical temperature, below which the thermal entanglement of considered spin chains is nonzero. We have shown that at those quantum-phase transitions, caused by multispin interactions, the thermal entanglement is reduced. Also, we have shown that the thermal entanglement is reduced due to nonzero magnetization of spin chains in the ground state, caused by multispin interactions.
Title:: Observation of strong magnetoelastic coupling in a first-order phase transition of CrOCl
Authors:: Angelkort, J; Wolfel, A; Schonleber, A; van Smaalen, S; Kremer, RK Author Full Names: Angelkort, Joachim; Woelfel, Alexander; Schoenleber, Andreas; van Smaalen, Sander; Kremer, Reinhard K.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 144416 OCT 2009
Abstract:: The phase transition of CrOCl toward a state of antiferromagnetic order below T-N=13.5 K has been identified as a first-order phase transition. The transition is accompanied by a lattice and structural distortion toward a twofold, 2b nuclear superstructure with a-axis unique monoclinic symmetry, as evidenced by temperature-dependent x-ray diffraction experiments. Magnetic-susceptibility and magnetization measurements indicate a transition with strong magnetoelastic coupling to a uniaxial antiferromagnet with ordered moments along c. A second transition is discovered at T-c approximate to 27.2 K that is presumably of purely magnetic origin and might indicate the formation of an incommensurate magnetic superstructure. The different behaviors of TiOCl, VOCl, and CrOCl are the result of the different symmetries of the filled 3d orbitals, which lead to different exchange interactions on the MO double layers of these isostructural compounds.
Title:: Formation of a well ordered ultrathin aluminum oxide film on icosahedral AlPdMn quasicrystal (vol 76, 094203, 2007)
Authors:: Longchamp, JN; Burkardt, S; Erbudak, M; Weisskopf, Y Author Full Names: Longchamp, J. -N.; Burkardt, S.; Erbudak, M.; Weisskopf, Y.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 149901 OCT 2009
Title:: Field suppression of the modulated phase of Ce2Pd2Sn
Authors:: Berisso, MG; Sereni, JG; Braghta, A; Schmerber, G; Chevalier, B; Kappler, JP Author Full Names: Gomez Berisso, M.; Sereni, J. G.; Braghta, A.; Schmerber, G.; Chevalier, B.; Kappler, J. P.
Source:: PHYSICA B-CONDENSED MATTER 404 (19): 2930-2933 OCT 15 2009
Abstract:: Low temperature magnetic (M) and thermal (C-p) properties of the intermetallic compound Ce2Pd2Sn have been investigated at zero and different magnetic fields. Two transitions were recognized at T-C = 2.1 K and T-M = 4.8 K, with latter nearly coinciding with the extrapolated Curie-Weiss temperature theta(p) = 4.5 K. The Curie factor evaluated from T >= T-M, is approximate to 2 mu(B) The positive value of theta(p), the triangular coordination of the magnetic (Ce) atoms and the weak effect of applied magnetic field, reveal that T-M cannot be considered as a canonic antiferromagnetic transition like claimed in the literature. M(T) measurements under moderate magnetic fields (0 <= B <= 2.5 kOe) show T-C(B) increasing while T-M(B) is practically not affected. Both transition merge in a critical point at T-cr = (4.3 +/- 0.3)K for B-cr = (2.1 +/- 0.3)kOe, where the intermediate phase is suppressed. At T-C = 2.2 K, the cusp of a first order transition is observed in C-p(T). According to the proposed ferromagnetic ground state, it is followed by a C-p(T)alpha T(3/2)exp(-E-g/T) dependence, with a gap of anisotropy E-g approximate to 7 K. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Antiferromagnetic structure in UNiAl at dilution temperatures
Authors:: Prokes, K; Bruck, E; Sechovsky, V Author Full Names: Prokes, K.; Bruck, E.; Sechovsky, V.
Source:: PHYSICA B-CONDENSED MATTER 404 (19): 3025-3027 OCT 15 2009
Abstract:: Neutron diffraction experiments in zero field reveals that the originally sine-wave-modulated antiferromagnetic structure in UNiAl starts to square-up at low temperatures. The squaring-up is, however, not completed even at 150 mK, most probably due to competing magnetic interactions. The fact that the magnetic moments are not equal at all the uranium atomic sites is responsible at least partially for the enhanced low-temperature-specific heat coefficient observed in UNiAl at low temperatures. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Resonant X-ray scattering study of Ca3Co2O6 ground state: Preliminary results of magnetic field effects
Authors:: Mazzoli, C; Bombardi, A; Agrestini, S; Lees, MR Author Full Names: Mazzoli, C.; Bombardi, A.; Agrestini, S.; Lees, M. R.
Source:: PHYSICA B-CONDENSED MATTER 404 (19): 3042-3044 OCT 15 2009
Abstract:: We present resonant magnetic X-ray scattering (RMXS) measurements in an applied magnetic field on a single crystal of Ca3Co2O6. We focus our attention on the transition from an incommensurate partially disordered antiferromagnetic state to a ferrimagnetic state: a lock-in and a divergence of the magnetic correlation length at the transition shed light on the nature of the ground state and on the c-axis vs. in-plane exchange couplings in this system. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Magnetic properties of the t-J model at low doping
Authors:: Falb, J; Neto, MBS; Muramatsu, A Author Full Names: Falb, J.; Silva Neto, M. B.; Muramatsu, A.
Source:: PHYSICA B-CONDENSED MATTER 404 (19): 3075-3078 OCT 15 2009
Abstract:: A path-integral for the t-J model in two dimensions is constructed based on Dirac quantization, with an action found originally by Wiegmann [Phys. Rev. Lett. 60 (1988) 821; Nucl. Phys. B 323 (1989) 311]. Concentrating on the low doping limit, we assume short range anti ferromagnetic order of the spin degrees of freedom. Going over to a local spin quantization axis of the dopant fermions that follows the spin degree of freedom, staggered CP1 fields result and the constraint against double occupancy can be resolved. The staggered CP1 fields are split into slow and fast modes, such that after a gradient expansion, and after integrating out the fast modes and the dopant fermions, a CP1 field-theory with a massive gauge field is obtained that describes generically incommensurate coplanar magnetic structures, as discussed previously in the context of frustrated quantum anti ferromagnets. The analysis of Landau damping shows that in this case, even in the presence of doping, the dynamical critical exponent z = 1. as a consequence of coupling of the dopant holes to a spin current, as opposed to a spin density. This result agrees with experimental observations in the underdoped region of high temperature superconductors, and departs from the one obtained by Hertz and Millis (z = 2) in the case of spin density waves in the Hubbard model. (C) 2009 Elsevier B.V. All rights reserved.
Title:: X-ray resonant scattering study of the magnetic phase diagram of multiferroic TbMnO3
Authors:: Walker, HC; Ewings, RA; Fabrizi, F; Mannix, D; Mazzoli, C; Wilkins, SB; Paolasini, L; Prabhakaran, D; Boothroyd, AT; McMorrow, DF Author Full Names: Walker, H. C.; Ewings, R. A.; Fabrizi, F.; Mannix, D.; Mazzoli, C.; Wilkins, S. B.; Paolasini, L.; Prabhakaran, D.; Boothroyd, A. T.; McMorrow, D. F.
Source:: PHYSICA B-CONDENSED MATTER 404 (19): 3264-3266 OCT 15 2009
Abstract:: We present the magnetic phase diagram of multiferroic TbMnO3 for H parallel to b determined using X-ray resonant scattering at the Tb L-3-edge. Investigations of two different magnetic domains, C-type and F-type, demonstrate very similar behaviour in high applied magnetic fields, with a low temperature incommensurate to commensurate transition at H similar or equal to 4.5T, concurrent with the polarisation flop observed in bulk magnetoelectric measurements. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Effect of Nonmagnetic Substituents Mg and Zn on the Phase Competition in the Multiferroic Antiferromagnet MnWO4
Authors:: Meddar, L; Josse, M; Deniard, P; La, C; Andre, G; Damay, F; Petricek, V; Jobic, S; Whangbo, MH; Maglione, M; Payen, C Author Full Names: Meddar, Lynda; Josse, Michael; Deniard, Philippe; La, Carole; Andre, Gilles; Damay, Francoise; Petricek, Vaclav; Jobic, Stephane; Whangbo, Myung-Hwan; Maglione, Mario; Payen, Christophe
Source:: CHEMISTRY OF MATERIALS 21 (21): 5203-5214 NOV 10 2009
Abstract:: The effects of substituting nonmagnetic Ma(2+) and Zn2+ ions for the Mn2+ (S = 5/2) ions oil the structural, magnetic, and dielectric properties of the multiferroic frustrated antiferromagnet MnWO4 were investigated Polycrystalline samples of Mn1-xMgxWO4 and Mn1-xZnxWO4 (0 <= x <= 0.3) solid Solutions were prepared via a solid-state route and characterized via X-ray and neutron diffraction, magnetization, and dielectric permittivity measurements. Mg and Zn substitutions result in very similar effects The Neel temperature (T-N), the AF3-to-AF2 magnetic phase-transition temperature (T-2), and the critical ferroelectric temperature (T-c = T-2) of MnWO4 are reduced upon nonmagnetic doping. At the lowest temperature (T = 1.5 K), the incommensurate magnetic Structure for x(Mg) = 0 15 and v(Zn) = 0.15 corresponds to either a sinusoidal spin arrangement or an elliptical spin-spiral phase similar to the polar AF2 structure observed in MnWO4 These findings were discussed by considering the effects of the Mg and Zn Substitutions oil the crystal lattice and on the spin exchange network of MnWO4.
Update: 5-Nov-2009
Title:: Crossover from incommensurate to commensurate magnetic orderings in CoCr2O4
Authors:: Chang, LJ; Huang, DJ; Li, WH; Cheong, SW; Ratcliff, W; Lynn, JW Author Full Names: Chang, L. J.; Huang, D. J.; Li, W-H; Cheong, S-W; Ratcliff, W.; Lynn, J. W.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (45): Art. No. 456008 NOV 11 2009
Abstract:: The conical spin order of multiferroic CoCr2O4 has been studied by a neutron diffraction to investigate its magnetic phase transitions at temperatures below 40 K. Magnetic order of a spiral spin component with an incommensurate propagation vector of (0.63, 0.63, 0) was observed at 26 K, while at 14.5 K, the incommensurate conical spin order showed a transition into the fixed commensurate propagation vector of (2/3, 2/3, 0). In addition, two satellite peaks with propagation vectors of (0.035, 0, 0) and (0, 0.035, 0) from the commensurate vector were observed. The widths of these peaks indicate a long-range magnetic order. This new magnetic configuration below 14.5 K may lead to a new model of multiferroic behavior differing from the well-known spin-current model for magnetic ferroelectricity.
Update: 29-Oct-2009
Title:: Electronic Self-Organization in the Single-Layer Manganite Pr1-xCa1+xMnO4
Authors:: Ye, F; Chi, SX; Fernandez-Baca, JA; Moreo, A; Dagotto, E; Lynn, JW; Mathieu, R; Kaneko, Y; Tokura, Y; Dai, PC Author Full Names: Ye, F.; Chi, Songxue; Fernandez-Baca, J. A.; Moreo, A.; Dagotto, E.; Lynn, J. W.; Mathieu, R.; Kaneko, Y.; Tokura, Y.; Dai, Pengcheng
Source:: PHYSICAL REVIEW LETTERS 103 (16): Art. No. 167202 OCT 16 2009
Abstract:: We use neutron scattering to investigate the doping evolution of the magnetic correlations in the single-layer manganite Pr1-xCa1-xMnO4, away from the x = 0.5 composition where the CE-type commensurate antiferromagnetic (AF) structure is stable. We find that short-range incommensurate spin correlations develop as the system is electron doped (x < 0.5), which coexist with the CE-type AF order. This suggests that electron doping in this system induces an inhomogeneous electronic self-organization, where commensurate AF patches with x = 0.5 are separated by electron-rich domain walls with short-range magnetic correlations. This behavior is strikingly different than for the perovskite Pr1-xCaxMnO3, where the long-range CE-type commensurate AF structure is stable over a wide range of electron or hole doping around x = 0.5.
Title:: Low temperature thermodynamical properties of ErCu2Si2
Authors:: Baran, S; Gondek, L; Szytula, A; Kaczorowski, D; Pikul, A; Penc, B; Piekarz, P; Hoser, A; Gerischer, S Author Full Names: Baran, S.; Gondek, L.; Szytula, A.; Kaczorowski, D.; Pikul, A.; Penc, B.; Piekarz, P.; Hoser, A.; Gerischer, S.
Source:: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (1): 12-18 JAN 2010
Abstract:: ErCu2Si2 crystallises in the tetragonal ThCr2Si2-type crystal structure. In this paper results of magnetometric, electrical transport, specific heat as well as neutron diffraction are reported. Results of electrical resistivity and specific heat measurements performed at low temperature yield existence of magnetic ordering roughly at 1.3 K. These results are in concert with neutron diffraction measurements, which reveal simple antiferromagnetic ordering between 0.47 and 1.00 K. At temperatures ranging from 1.00 up to 1.50K an additional incommensurate magnetic structure was observed. The propagation vector kappa = (0;0;0.074) was proposed to describe magnetic reflections within the amplitude modulated magnetic structure. Basing on specific heat studies the crystal field levels splitting scheme and magnetic entropy were calculated. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Competing magnetic structures in the DySi FeB-type phase diagram
Authors:: Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Ritter, C; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Ritter, C.; Buschow, K. H. J.
Source:: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (1): 119-132 JAN 2010
Abstract:: The temperature magnetic phase diagrams, of the dimorphic DySi compound, have been studied in terms of wave vectors in the range 1.5-45 K, by neutron diffraction. The polycrystalline sample consists of 26% of CrB-type (Cmcm no. 63, all atoms at 4c site: (0, y, 1/4)) and of 74% of FeB-type (Pnma no. 62, all atoms at 4c site: (x, 1/4, z)). The CrB-ordering is described by the wave vector: q(1) = (0, 0, 1/2) over the entire magnetically ordered regime with a uniaxial magnetic structure along the shortest axis c. The FeB-type magnetic phase diagram reveals three distinct regions of magnetic ordering below T-N and one first order transition at T-2=23.5K (on heating). The ordering is described by two symmetry independent magnetic vectors q(2)=(0, 1/2,1/6) and q(3)=(0, q(3y), q(3z)) with a temperature variable length. At 1.5 K q(3y) approximate to 1/2 and q(3z) approximate to 1/11. The two phases coexist in the form of domains. They differ in the moment orientation of the q(3) phase that deviates by similar to 22 degrees from the b-axis in the (0, 0, 1) plane. The low temperature range (LT) 1.5 K-T-2 subdivides into two regions: (i) LT-1, between 1.5 K-T-1 where the relative amount of the two phases remains unchanged and in (ii) LT-2: T-1-T-2 where the amount of the incommensurate q3 phase increases at the cost of the commensurate q(2) amplitude modulated structure which remains unchanged but fully disappears at the first order transition at T-2=23.5 K. The q(3) phase undergoes minor changes until 22 K and gets destabilised at T-2 where the q(3z) component jumps from the LT value q(3z) approximate to 1/11 to the HT value approximate to 1/7 and the q(3y) component increases from 0.484(1) to 0.495(1). (iii) The high temperature (HT) range T-2-T-N (T-N=40 +/- 1 K) is described by a single wave vector q(3). The disproportionation of the HT magnetic phase q(3) below T-2 into two coexisting distinct phases q(2), q(3) down to 1.5 K is an unusual phenomenon, to our knowledge observed for the first time. Various mechanisms are discussed. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Self-similar transformation and quasi-unit cell construction of quasi-periodic structure with twelve-fold rotational symmetry
Authors:: Liao, LG; Fu, H; Fu, XJ Author Full Names: Liao Long-Guang; Fu Hong; Fu Xiu-Jun
Source:: ACTA PHYSICA SINICA 58 (10): 7088-7093 OCT 2009
Abstract:: The structural properties of a quasicrystal model with twelve-fold rotational symmetry are studied. We correct the errors in the self-similar transformation of the square-rhombus-hexagon tiling model proposed by Socolar. Based on the Stampfli-Gahler square-rhombus-triangle tiling model, the quasi-unit cell is successfully constructed, which can describe the dodecagonal quasiperiodic structure by the covering theory.
Title:: Measurement of anisotropy thermopower of decagonal AlCuCo quasicrystal
Authors:: Fan, ZJ; Geng, XW; Kong, WJ; Jin, YR Author Full Names: Fan Zhen-Jun; Geng Xue-Wen; Kong Wen-Jie; Jin Yi-Rong
Source:: ACTA PHYSICA SINICA 58 (10): 7119-7123 OCT 2009
Abstract:: The thermopower of decagonal AlCuCo quasicrystal was measured in the periodic and quasiperiodic direction by laser heating alternating current measurement method in the temperature range of from 300 K to 1200 K. We found that the thermopower is negative in the periodic direction and positive in the quasiperiodic direction. The thermopower hopps at 1123 K (850 degrees C) along the periodic direction. The change of the thermopower is not monotonic at high temperature. The measurement method we used is sensitive to the phase transition point.
Title:: Multiresolution of quasicrystal diffraction spectra
Authors:: Elkharrat, A; Gazeau, JP; Denoyer, F Author Full Names: Elkharrat, Avi; Gazeau, Jean-Pierre; Denoyer, Francoise
Source:: ACTA CRYSTALLOGRAPHICA SECTION A 65: 466-489 Part 6 NOV 2009
Abstract:: A method for analyzing and classifying two-dimensional pure point diffraction spectra (i.e. a set of Bragg peaks) of certain self-similar structures with scaling factor beta > 1, such as quasicrystals, is presented. The two-dimensional pure point diffraction spectrum Pi is viewed as a point set in the complex plane in which each point is assigned a positive number, its Bragg intensity. Then, by using a nested sequence of self-similar subsets called beta-lattices, we implement a multiresolution analysis of the spectrum Pi. This analysis yields a partition of Pi simultaneously in geometry, in scale and in intensity (the 'fingerprint' of the spectrum, not of the diffracting structure itself). The method is tested through numerical explorations of pure point diffraction spectra of various mathematical structures and also with the diffraction pattern of a realistic model of a quasicrystal.
Update: 22-Oct-2009
Title:: Magnetic Properties of Multiferroics Bi(1-x)A(x)FeO(3-x/2) (A = Ca, Sr, Pb, Ba)
Authors:: Troyanchuk, IO; Mantytskaya, OS; Chobot, AN; Tereshko, NV Author Full Names: Troyanchuk, I. O.; Mantytskaya, O. S.; Chobot, A. N.; Tereshko, N. V.
Source:: PHYSICS OF THE SOLID STATE 51 (10): 2105-2108 OCT 2009
Abstract:: The magnetic properties of Bi(1-x)A(x)FeO(3-x/2) (A is an alkaline-earth ion) solid solutions have been studied in magnetic fields of up to 140 kOe. The ferroelectric phase (space group R3c) transforms into the nonpolar pseudocubic phase at x approximate to 0.2. It is demonstrated that the substitution of alkaline-earth ions for bismuth ions (x >= 0.1) leads to a complete destruction of the modulated antiferromagnetic structure and the appearance of a weakly ferromagnetic state within the R3c state. In the pseudocubic phase, the spontaneous magnetization is absent; however, the field dependence of the magnetization is nonlinear and depends on the magnetic prehistory.
Title:: MATERIALS SCIENCE Quasicrystals from nanocrystals
Authors:: van Blaaderen, A Author Full Names: van Blaaderen, Alfons
Source:: NATURE 461 (7266): 892-893 OCT 15 2009
Title:: Quasicrystalline order in self-assembled binary nanoparticle superlattices
Authors:: Talapin, DV; Shevchenko, EV; Bodnarchuk, MI; Ye, XC; Chen, J; Murray, CB Author Full Names: Talapin, Dmitri V.; Shevchenko, Elena V.; Bodnarchuk, Maryna I.; Ye, Xingchen; Chen, Jun; Murray, Christopher B.
Source:: NATURE 461 (7266): 964-967 OCT 15 2009
Abstract:: The discovery of quasicrystals in 1984 changed our view of ordered solids as periodic structures (1,2) and introduced new long-range-ordered phases lacking any translational symmetry(3-5). Quasi-crystals permit symmetry operations forbidden in classical crystallography, for example five-, eight-, ten-and 12-fold rotations, yet have sharp diffraction peaks. Intermetallic compounds have been observed to form both metastable and energetically stabilized quasicrystals (1,3,5); quasicrystalline order has also been reported for the tantalum telluride phase with an approximate Ta1.6Te composition(6). Later, quasicrystals were discovered in soft matter, namely supramolecular structures of organic dendrimers(7) and tri-block copolymers(8), and micrometre-sized colloidal spheres have been arranged into quasicrystalline arrays by using intense laser beams that create quasi-periodic optical standing-wave patterns(9). Here we show that colloidal inorganic nanoparticles can self-assemble into binary aperiodic superlattices. We observe formation of assemblies with dodecagonal quasicrystalline order in different binary nanoparticle systems: 13.4-nm Fe2O3 and 5-nm Au nanocrystals, 12.6-nm Fe3O4 and 4.7-nm Au nanocrystals, and 9-nm PbS and 3-nm Pd nanocrystals. Such compositional flexibility indicates that the formation of quasicrystalline nanoparticle assemblies does not require a unique combination of interparticle interactions, but is a general sphere-packing phenomenon governed by the entropy and simple interparticle potentials. We also find that dodecagonal quasicrystalline superlattices can form low-defect interfaces with ordinary crystalline binary superlattices, using fragments of (3(3).4(2)) Archimedean tiling as the 'wetting layer' between the periodic and aperiodic phases.
Title:: Magnetic structures of quaternary intermetallic borocarbides RCo2B2C (R = Dy, Ho, Er)
Authors:: ElMassalami, M; Moreno, R; Takeya, H; Ouladdiaf, B; Lynn, JW; Freitas, RS Author Full Names: ElMassalami, M.; Moreno, R.; Takeya, H.; Ouladdiaf, B.; Lynn, J. W.; Freitas, R. S.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (43): Art. No. 436006 OCT 28 2009
Abstract:: The magnetic structures of the title compounds have been studied by neutron diffraction. In contrast to the isomorphous RNi2B2C compounds, wherein a variety of exotic incommensurate modulated structures has been observed, the magnetic structure of ErCo2B2C is found to be a collinear antiferromagnet with k = (12, 0, 12) while those of HoCo2B2C and DyCo2B2C are observed to be simple ferromagnets. For all studied compounds, the moments are found to be confined within the basal plane and their magnitudes are comparable to the values obtained from the low-temperature isothermal magnetization measurements. The absence of modulated magnetic structures in the RCo2B2C series (for ErCo2B2C, verified down to 50 mK) is attributed to the quenching of the Fermi surface nesting features.
Title:: A comparative study of the magnetic properties of the 1/1 approximant Ag50In36Gd14 and the icosahedral quasicrystal Ag50In36Gd14
Authors:: Wang, P; Stadnik, ZM; Al-Qadi, K; Przewoznik, J Author Full Names: Wang, P.; Stadnik, Z. M.; Al-Qadi, K.; Przewoznik, J.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (43): Art. No. 436007 OCT 28 2009
Abstract:: We report on measurements of the dc and ac magnetic susceptibility, Gd-155 Mossbauer spectra, and specific heat of the 1/1 approximant Ag50In36Gd14, and of the ac magnetic susceptibility of the icosahedral quasicrystal Ag50In36Gd14. These alloys are shown to be spin glasses. For the icosahedral quasicrystal Ag50In36Gd14, spin freezing occurs at T-f = 4.3 K, and the frequency dependence of T-f is well accounted for by the Vogel-Fulcher and power laws. Spin freezing in the 1/1 approximant Ag50In36Gd14 occurs in two stages: at T-f1 = 3.7 K, Gd spins develop short-range correlations but continue to fluctuate, and then long-range freezing is achieved at T-f2 = 2.4 K. The frequency dependences of T-f1 and T-f2 can be accounted for by means of the Vogel-Fulcher law and the critical slowing down dynamics. It is shown that the spin freezing in both alloys is a nonequilibrium phenomenon rather than a true equilibrium phase transition. The Gd-155 Mossbauer spectra of the 1/1 approximant Ag50In36Gd14 confirm that the Gd spins are frozen at 1.5 K and are fluctuating at 4.6 K. The magnetic specific heat exhibits a maximum at a temperature that is 30% larger than T-f1, but the temperature derivative of the magnetic entropy peaks at T-f1. The Debye temperature of the 1/1 approximant Ag50In36Gd14 is 199(1) K as determined from the Mossbauer data, and 205(2) K as determined from the specific heat data.
Title:: Processing and characterization of rapidly quenched Ti-based alloys: Influence of solidification rate on the as-quenched structures
Authors:: Lefaix, H; Vermaut, P; Janickovic, D; Svec, P; Portier, R; Prima, F Author Full Names: Lefaix, H.; Vermaut, P.; Janickovic, D.; Svec, P.; Portier, R.; Prima, F.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 483 (1-2): 168-172 AUG 26 2009
Abstract:: >From technological viewpoint. icosahedral Ti-Zr-Ni phase may give challenging opportunities as novel hydrogen storage and hydride battery. Nevertheless. from the structural standpoint, the phase selection criterion as function of solidification route remains unclear. A series of Ti45Zr38Ni17 alloys, known to provide stable and well-ordered quasicrystals, was produced by planar flow casting using different processing parameters. From structural characterization, it appears that, at high cooling rate, i.e. high wheel speeds, or for the highest temperature of the melt, the as-quenched sample exhibits a mixture of nanoscale P and amorphous phases. The icosahedral phase precipitates when decreasing the wheel speed, from lower temperatures of the melt or after annealing a crystallized amorphous matrix. The reproducible formation of quasicrystals, observed in the amorphous matrix containing P particles, corroborates the competition between icosahedral and body-centered cubic (bcc) phases during the solidification process. These results are promising since it could be possible to control volume fractions of these two phases by choosing well-fitted thermal treatments so that quasicrystals mechanical properties should be improved by dispersion of a stable bcc phase. (C) 2008 Elsevier B.V. All rights reserved.
Title:: Multi-scaled polymer-based composite materials synthesized by mechanical alloying
Authors:: Kaloshkin, SD; Vandi, LJ; Tcherdyntsev, VV; Shelekhov, EV; Danilov, VD Author Full Names: Kaloshkin, S. D.; Vandi, L. -J.; Tcherdyntsev, V. V.; Shelekhov, E. V.; Danilov, V. D.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 483 (1-2): 195-199 AUG 26 2009
Abstract:: Multi-scaled composite materials are of great importance, because they exhibit higher mechanical properties than those attained using conventional fillers or polymer blends. In this work, multi-scaled composite materials based on ultra-high-molecular weight polyethylene (UHMWPE), quasicrystals, polyimide and bronze are investigated for use in the moving parts of machines, gears, bearings, and sliding elements. The main object is to investigate the process of fabricating such composite materials, and to check if these materials are reproducible and reliable to an industrial extent. The specimens were prepared using a high-energy planetary mill. When milled with bronze, the quasicrystalline phase was dissolved into an intermetallic solid solution: milling with polymers showed to conserve the quasicrystalline phase, whereas the crystallization of UHMWPE was achieved during the milling process. Tribological study of consolidated samples showed an increase in the wear resistance for the bronze-containing composite materials. in comparison with pure UHMWPE, the polyimide-based specimen exhibited higher strength and hardness. This work has demonstrated the possibility of producing composite materials with acceptable and reliable properties using the mechanical alloying technology. (C) 2008 Elsevier B.V. All rights reserved.
Title:: Nanostructure controlling in Zr-based metallic glasses using icosahedral local structure
Authors:: Saida, J; Kato, H; Setyawan, AD; Yoshimi, K; Inoue, A Author Full Names: Saida, J.; Kato, H.; Setyawan, A. D.; Yoshimi, K.; Inoue, A.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 483 (1-2): 231-234 AUG 26 2009
Abstract:: Glass-nano(quasi)crystal composite materials based on Zr-Al-Ni-Cu metallic glasses have been synthesized by controlling the nucleation and growth rates of the precipitated phase correlated with a unique icosahedral local structure. It is well known that the Zr65Al7.5Ni10Cu17.5 metallic glass has a high glass-forming ability (GFA), which enables us to produce the glassy sample with a bulky shape. Controlling a substitution of QC-forming elements such as noble metals with Cu and annealing condition, the nanoscale icosahedral quasicrystalline phase (I-phase) with various grain sizes and nucleus densities can be formed. Moreover, we have succeeded to control the nano-QC phase nucleation by changing the atmosphere pressure during casting, which results in the formation of new bulk metallic glasses (BMGs). These nanoscale structure and nucleation controlling techniques in BMGs bring a significant improvement of mechanical properties such as high strength and good ductility. (C) 2008 Elsevier B.V. All rights reserved.
Title:: Characterization of phases in complex metallic alloys Al73Mn27-xFex (x=2, 4 and 6)
Authors:: Priputen, P; Kusy, M; Kriska, M; Lipka, R; Illekova, E; Svec, P; Bursik, J; Svoboda, M; Dolinsek, J; Janovec, J Author Full Names: Priputen, P.; Kusy, M.; Kriska, M.; Lipka, R.; Illekova, E.; Svec, P.; Bursik, J.; Svoboda, M.; Dolinsek, J.; Janovec, J.
Source:: INTERMETALLICS 17 (12): 1047-1051 DEC 2009
Abstract:: The characterization of phases in Al73Mn27-xFex (x = 2, 4 and 6) alloys was performed using X-ray diffraction, differential thermal analysis, and scanning electron microscopy enabling energy dispersive X-ray spectroscopy. Both the annealed and the thermally cycled states were studied. In the annealed states the occurrence of T-phase was expected, however it was confirmed for alloys Al73Mn25Fe2 and Al73Mn23Fe4 only. The annealing of the Al73Mn21Fe6 alloy probably led to the formation of decagonal quasicrystal (D). The T- and D-phases were found to be unstable at low temperatures. In the states after DTA the low temperature Al-11(Mn,Fe)(4) and gamma(2) phases were observed in the Al73Mn25Fe2 and Al73Mn21Fe6 alloys, while only the former phase was observed in the Al73Mn23Fe4 alloy. (C) 2009 Elsevier Ltd. All rights reserved.
Title:: Structure Determination of Two Modulated gamma-Brass Structures in the Zn-Pd System through a (3+1)-Dimensional Space Description
Authors:: Gourdon, O; Izaola, Z; Elcoro, L; Petricek, V; Miller, GJ Author Full Names: Gourdon, Olivier; Izaola, Zunbeltz; Elcoro, Luis; Petricek, Vaclav; Miller, Gordon J.
Source:: INORGANIC CHEMISTRY 48 (20): 9715-9722 OCT 19 2009
Abstract:: The structure determination of two composite compounds in the Zn-Pd system with close relationships to the cubic gamma-brass structure Zn11-delta Pd2+delta is reported. Their structures have been solved from single crystal X-ray diffraction data within a (3 + 1)-dimensional [(3 + 1)D] formalism. Zn75.7(7)Pd24.3 and Zn78.8(7)Pd21.2 crystallize with orthorhombic symmetry, superspace group Xmmm(00 gamma)0s0 (X [(1/2,1/2,0,0); (0,1/2,1/2,1/2); (1/2,0,1/2,1/2)]), with the following lattice parameters, respectively: a(s) = 12.929(3) angstrom, b(s) = 9.112(4) angstrom, c(s) = 2.5631(7) angstrom, q = 8/13 c* and V-s = 302.1(3) angstrom(3) and a(s) = 12.909(3) angstrom, b(s) = 9.115(3) angstrom, c(s) = 2.6052(6) angstrom, q = 11/18 c* and V-s = 306.4(2) angstrom(3). Their structures may be considered as commensurate because they can be refined in the conventional 3D space groups (Cmce and Cmcm, respectively) using supercells, but they also refined within the (3 + 1)D formalism to residual factors R = 3.14% for 139 parameters and 1184 independent reflections for Zn75.7(7)Pd24.3 and R = 3.16% for 175 parameters and 1804 independent reflections for Zn78.8(7)Pd21.2. The use of the (3 + 1)D formalism improves the results of the refinement and leads to a better understanding of the complexity of the atomic arrangement through the various modulations (occupation waves and displacive waves). Our refinements emphasize a unique Pd/Zn occupancy modulation at the center of distorted icosahedra, a modulation which correlates with the distortion of these polyhedra.
Title:: Nanoquasicrystalline Al-Fe-Cr-based alloys. Part I: Phase transformations
Authors:: Galano, M; Audebert, F; Stone, IC; Cantor, B Author Full Names: Galano, M.; Audebert, F.; Stone, I. C.; Cantor, B.
Source:: ACTA MATERIALIA 57 (17): 5107-5119 OCT 2009
Abstract:: Nanoquasicrystalline Al-Fe-Cr-based alloys composed of sub-micro-sized icosahedral quasicrystalline particles embedded in alpha-Al matrix have a higher strength at elevated temperature compared with commercial Al alloys. However, further improvement of the microstructural stability is desirable in order to maximize the elevated temperature strength. A detailed study of the effect on the microstructure and the phase transformations by the addition of Ti, V, Nb or Ta to a ternary Al-93(Fe3Cr2)(7) alloy was carried out using heat treatment and microstructural characterization. The addition of the fourth element leads to a refined microstructure and can stabilize the icosahedral topology, delaying the quasicrystalline icosahedral phase decomposition until a higher temperature is reached. The addition of Nb or Ta enabled a greater stabilization effect than the addition of Ti or V, retaining a microstructure similar to the as-spun state after heat treatment between 450 and 550 degrees C and even retaining icosahedral particles up to 550 degrees C. The outstanding microstructural stabilization obtained with addition of Nb or Ta leads to very promising applications in the automotive and aeronautic industries. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Update: 15-Oct-2009
Title:: Nonmetallic Nature of the Interrelation of Thermal, Magnetic, and Electrical Properties in Icosahedral Quasicrystals at High Temperatures
Authors:: Prekul, AF; Shchegolikhina, NI; Nazarova, SZ; Edagawa, K Author Full Names: Prekul, A. F.; Shchegolikhina, N. I.; Nazarova, S. Z.; Edagawa, K.
Source:: PHYSICS OF METALS AND METALLOGRAPHY 108 (2): 120-124 AUG 2009
Abstract:: In the icosahedral phase of Al-Cu-Fe alloys in the temperature range above 300 K there has been found an interrelation between the heat capacity, magnetic susceptibility, and conductivity not characteristic of typical metals. It is supposed that these phases are systems whose properties at finite temperatures are predominantly determined by excited electrons rather than by electrons with a Fermi energy E-F.
Title:: Spin Amplitude Modulation Driven Magnetoelectric Coupling in the New Multiferroic FeTe2O5Br
Authors:: Pregelj, M; Zaharko, O; Zorko, A; Kutnjak, Z; Jeglic, P; Brown, PJ; Jagodic, M; Jaglicic, Z; Berger, H; Arcon, D Author Full Names: Pregelj, M.; Zaharko, O.; Zorko, A.; Kutnjak, Z.; Jeglic, P.; Brown, P. J.; Jagodic, M.; Jaglicic, Z.; Berger, H.; Arcon, D.
Source:: PHYSICAL REVIEW LETTERS 103 (14): Art. No. 147202 OCT 2 2009
Abstract:: The magnetic and ferroelectric properties of the layered geometrically frustrated cluster compound FeTe2O5Br were investigated with single-crystal neutron diffraction and dielectric measurements. An incommensurate transverse amplitude modulated magnetic order with the wave vector q = (1/2, 0.463, 0) develops below T-N = 10.6(2) K. Simultaneously, a ferroelectric order due to exchange striction involving polarizable Te4+ lone-pair electrons develops perpendicular to q and to Fe3+ magnetic moments. The observed magnetoelectric coupling is proposed to originate from the temperature dependent phase difference between neighboring amplitude modulation waves.
Title:: Magnetic structure and ferroelectric polarization of MnWO4 investigated by density functional calculations and classical spin analysis
Authors:: Tian, C; Lee, CH; Xiang, HJ; Zhang, YM; Payen, C; Jobic, S; Whangbo, MH Author Full Names: Tian, Chuan; Lee, Changhoon; Xiang, Hongjun; Zhang, Yuemei; Payen, Christophe; Jobic, Stephane; Whangbo, Myung-Hwan
Source:: PHYSICAL REVIEW B 80 (10): Art. No. 104426 SEP 2009
Abstract:: The ordered magnetic states of MnWO4 at low temperatures were examined by evaluating the spin exchange interactions between the Mn2+ ions of MnWO4 on the basis of first principles density functional calculations and by performing classical spin analysis with the resulting spin exchange parameters. Our work shows that the spin exchange interactions are frustrated within each zigzag chain of Mn2+ ions along the c direction and between such chains of Mn2+ ions along the a direction. This explains the occurrence of a spiral-spin order along the c and a directions in the incommensurate magnetic state AF2, and that of a up arrow up arrow down arrow down arrow spin order along the c and a directions in the commensurate magnetic state AF1. The ferroelectric polarization of MnWO4 in the spiral-spin state AF2 was examined by performing Berry phase calculations for a model superstructure to find that the ferroelectric polarization occurs along the b direction,! in agreement with experiment.
Title:: Magnetic and crystal structure of Ho-5(SixGe(1-x))(4) studied by neutron diffraction
Authors:: Ritter, C; Magen, C; Morellon, L; Algarabel, PA; Ibarra, MR; Pereira, AM; Araujo, JP; Sousa, JB Author Full Names: Ritter, C.; Magen, C.; Morellon, L.; Algarabel, P. A.; Ibarra, M. R.; Pereira, A. M.; Araujo, J. P.; Sousa, J. B.
Source:: PHYSICAL REVIEW B 80 (10): Art. No. 104427 SEP 2009
Abstract:: The magnetic and crystal structures of the magnetocaloric Ho-5(SixGe1-x)(4) (x= 1, 0.75, 0.5 and 0) have been studied by neutron powder diffraction experiments. The room-temperature crystal phases of the compositions x= 1, 0.75, and 0.5 are preserved in the whole temperature range 2-300 K, i.e. the Gd5Si4-type Pnma O(I) structure for Ho5Si4, the Gd5Si2Ge2-type P112(1)/a M state in x= 0.75, and the Sm5Ge4-type Pnma O(II) phase in x= 0.5. Ho5Si4 undergoes a second order ferromagnetic (FM) transition at T-C= 77 K into a noncollinear FM structure with the magnetization oriented mainly along the a axis and weak antiferromagnetic (AFM) coupling along b and c (magnetic space group Pnm'a'). Ho5Si3Ge becomes FM at T-C= 50 K (magnetic space group P112(1)'/a). At T-C'similar to 16 K an incipient second incommensurate magnetic phase appears which becomes commensurate below 8 K with a propagation vector k=(0 0 1/4). The magnetic structure of the main phase at 30 and 2 K shows the dominance of a FM coupling along the a axis with an AFM canting along c. Ho5Si2Ge2 stands out for the complexity of its low-temperature magnetic structure. In addition to the Neel transition of the O(II) phase at T-N similar to 30 K (magnetic space group Pn'm'a'), two additional magnetic phases with propagation vectors k=(0 0 1/4) and k=(1/2 0 0) appear at 15 and 12 K, respectively. In Ho5Ge4 the main O(II) structure orders AFM with k=(0 0 0) at T-N similar to 30 K in the same magnetic space group Pn'm'a'. Below 25 K a complete structural transition from high temperature O(II)Pnma to P2(1)/m takes place within the AFM state. The magnetic structure of this new nuclear phase stays AFM with k=(0 0 0), but sees two out of six independent Ho sites non magnetic. A second magnetic transition takes place at about 18 K characterized by the appearance of a second propagation vector k=(0 0 1/2) which magnetically couples the formerly non magnetic Ho sites. Magnetic- field dependent neutron diffractograms demonstrate that FM sets in in Ho5Ge4. The onset of ferromagnetism is associated with the previously reported nucleation of a new high field O(II) Pnma phase. Contrary to the intensity of the magnetic coupling with the propagation vector k=(0 0 0), which disappears quickly with the onset of FM, a progressive decrease of the intensity associated with the state k=(0 0 1/2) suggests a possible relationship between the extent of the magnetic coupling k=(0 0 1/2) and the percentage of remnant P2(1)/m phase.
Title:: Short-range incommensurate magnetic order near the superconducting phase boundary in Fe(1+delta)Te(1-x)Sex
Authors:: Wen, JS; Xu, GY; Xu, ZJ; Lin, ZW; Li, Q; Ratcliff, W; Gu, G; Tranquada, JM Author Full Names: Wen, Jinsheng; Xu, Guangyong; Xu, Zhijun; Lin, Zhi Wei; Li, Qiang; Ratcliff, W.; Gu, Genda; Tranquada, J. M.
Source:: PHYSICAL REVIEW B 80 (10): Art. No. 104506 SEP 2009
Abstract:: We performed elastic neutron-scattering and magnetization measurements on Fe1.07Te0.75Se0.25 and FeTe0.7Se0.3. Short-range incommensurate magnetic order is observed in both samples. In the former sample with higher Fe content, a broad magnetic peak appears around (0.46,0,0.5) at low temperature, while in FeTe0.7Se0.3, the broad magnetic peak is found to be closer to the antiferromagnetic (AFM) wave vector (0.5,0,0.5). The incommensurate peaks are only observed on one side of the AFM wave vector for both samples, which can be modeled in terms of an imbalance of ferromagnetic/antiferromagnetic correlations between nearest-neighbor spins. We also find that with higher Se (and lower Fe) concentration, the magnetic order becomes weaker while the superconducting temperature and volume increase.
Title:: Stability of nodal quasiparticles in underdoped YBa2Cu3O6+y probed by penetration depth and microwave spectroscopy
Authors:: Huttema, WA; Bobowski, JS; Turner, PJ; Liang, RX; Hardy, WN; Bonn, DA; Broun, DM Author Full Names: Huttema, W. A.; Bobowski, J. S.; Turner, P. J.; Liang, Ruixing; Hardy, W. N.; Bonn, D. A.; Broun, D. M.
Source:: PHYSICAL REVIEW B 80 (10): Art. No. 104509 SEP 2009
Abstract:: High-resolution measurements of superfluid density rho(s)(T) and broadband quasiparticle conductivity sigma(1)(Omega) have been used to probe the low-energy excitation spectrum of nodal quasiparticles in underdoped YBa2Cu3O6+y. Penetration depth lambda(T) is measured to temperatures as low as 0.05 K. sigma 1(Omega) is measured from 0.1 to 20 GHz and is a direct probe of zero-energy quasiparticles. The data are compared with predictions for a number of theoretical scenarios that compete with or otherwise modify pure d(x2-y2) superconductivity, in particular, commensurate and incommensurate spin and charge-density waves; d(x2-y2) + is and d(x2-y2) + id(xy) superconductivity; circulating current phases; and the BCS-BEC crossover. We conclude that the data are consistent with a pure d(x2-y2) state in the presence of a small amount of strong scattering disorder, and are able to rule out most candidate competing states either completely or to a level set by the energy scale of the disorder, T-d similar to 4 K. Commensurate spin and charge-density orders, however, are not expected to alter the nodal spectrum and therefore cannot be excluded.
Title:: Structure of the fivefold surface of the Ag-In-Yb icosahedral quasicrystal
Authors:: Sharma, HR; Shimoda, M; Sagisaka, K; Takakura, H; Smerdon, JA; Nugent, PJ; McGrath, R; Fujita, D; Ohhashi, S; Tsai, AP Author Full Names: Sharma, H. R.; Shimoda, M.; Sagisaka, K.; Takakura, H.; Smerdon, J. A.; Nugent, P. J.; McGrath, R.; Fujita, D.; Ohhashi, S.; Tsai, A. P.
Source:: PHYSICAL REVIEW B 80 (12): Art. No. 121401 SEP 2009
Abstract:: The surface structural study of an icosahedral (i) quasicrystal of the Cd-Yb family is presented. Comparison of bias-dependent scanning tunneling microscopy data from the fivefold surface of i-Ag-In-Yb with the refined bulk model of isostructural i-Cd-Yb indicates that surfaces are formed at bulk planes intersecting the center of the rhombic triacontahedral clusters, the building blocks of the Cd-Yb family quasicrystals. These observations open up the possibility of the use of this material as a template for epitaxial structures.
Title:: Electronic structure of RNiC2 (R = Sm, Gd, and Nd) intermetallic compounds
Authors:: Laverock, J; Haynes, TD; Utfeld, C; Dugdale, SB Author Full Names: Laverock, J.; Haynes, T. D.; Utfeld, C.; Dugdale, S. B.
Source:: PHYSICAL REVIEW B 80 (12): Art. No. 125111 SEP 2009
Abstract:: First-principles calculations of the electronic structure of members of the RNiC2 series are presented and their Fermi surfaces investigated for nesting propensities, which might be linked to the charge-density waves exhibited by certain members of the series (R=Sm, Gd, and Nd). Calculations of the generalized susceptibility, chi(0)(q, omega), show strong peaks at the same q vector in both the real and imaginary parts for these compounds. Moreover, this peak occurs at a wave vector which is very close to that experimentally observed in SmNiC2. In contrast, for LaNiC2 (which is a superconductor below 2.7 K) as well as for ferromagnetic SmNiC2, there is no such sharp peak. This could explain the absence of a charge-density wave transition in the former, and the destruction of the charge-density wave that has been observed to accompany the onset of ferromagnetic order in the latter.
Title:: Theoretical study of the magnetism in the incommensurate phase of TiOCl
Authors:: Mastrogiuseppe, DM; Torio, ME; Gazza, CJ; Dobry, AO Author Full Names: Mastrogiuseppe, D. M.; Torio, M. E.; Gazza, C. J.; Dobry, A. O.
Source:: PHYSICA B-CONDENSED MATTER 404 (18): 2805-2808 OCT 1 2009
Abstract:: Going beyond a recently proposed microscopic model [D. Mastrogiuseppe. A. Dobry, arXiv:0810.3018v] for the incommensurate transition in the spin-Peierls TiOX (X = Cl, Br) compounds, in the present work we start by studying the thermodynamics of the model with XY spins and adiabatic phonons. We find that the system enters an incommensurate phase by a first order transition at a low temperature T-c1. At a higher temperature T-C2 a continuous transition to a uniform phase is found. Furthermore, we study the magnetism in the incommensurate phase by density matrix renormalization group (DMRG) calculations on a one-dimensional Heisenberg model where the exchange is modulated by the incommensurate atomic position pattern. When the wave vector q of the modulation is near pi, we find local magnetized zones (LMZ) in which spins abandon their singlets as a result of the domain walls induced by the modulated distortion. When q moves far away enough from pi, the LMZ disappear and the system develops incommensurate magnetic correlations induced by the structure. We discuss the relevance of this result regarding previous and future experiments in TiOCl (C) 2009 Elsevier B.V. All rights reserved.
Title:: Frustration of Magnetic and Ferroelectric Long-Range Order in Bi2Mn4/3Ni2/3O6
Authors:: Claridge, JB; Hughes, H; Bridges, CA; Allix, M; Suchomel, MR; Niu, H; Kuang, X; Rosseinsky, MJ; Bellido, N; Grebille, D; Perez, O; Simon, C; Pelloquin, D; Blundell, SJ; Lancaster, T; Baker, PJ; Pratt, FL; Halasyamani, PS Author Full Names: Claridge, John B.; Hughes, Helen; Bridges, Craig A.; Allix, Mathieu; Suchomel, Matthew R.; Niu, Hongjun; Kuang, Xiaojun; Rosseinsky, Matthew J.; Bellido, Natalia; Grebille, Dominique; Perez, Olivier; Simon, Charles; Pelloquin, Denis; Blundell, Stephen J.; Lancaster, Tom; Baker, Peter J.; Pratt, Francis L.; Halasyamani, P. Shiv
Source:: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 131 (39): 14000-14017 OCT 7 2009
Abstract:: The slight incommensurate modulation of the structure of Bi2Mn4/3Ni2/3O6 is sufficient to suppress the electrical polarization which arises in commensurate treatments of the structure, due to antiferroelectric coupling of local polar units of over 900 angstrom(3). The incommensurate structure is produced by the competition between ferroelectric Bi lone pair-driven A site displacement, chemical order of Mn and Ni on the B site, and both charge and orbital order at these transition metals. The interplay between the frustrated polar Bi displacements and the frustrated spin order at the B site, induced by positional disorder, produces magnetodielectric coupling between the incommensurately modulated lattice and the spin-glass-like ground state with an unusual relationship between the magnetocapacitance and the applied field.
Title:: Molecular dewetting on insulators
Authors:: Burke, SA; Topple, JM; Grutter, P Author Full Names: Burke, S. A.; Topple, J. M.; Gruetter, P.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (42): Art. No. 423101 OCT 21 2009
Abstract:: Recent attention given to the growth and morphology of organic thin films with regard to organic electronics has led to the observation of dewetting (a transition from layer (s) to islands) of molecular deposits in many of these systems. Dewetting is a much studied phenomenon in the formation of polymer and liquid films, but its observation in thin films of the 'small' molecules typical of organic electronics requires additional consideration of the structure of the interface between the molecular film and the substrate. This review covers some key concepts related to dewetting and molecular film growth. In particular, the origins of different growth modes and the thickness dependent interactions which give rise to dewetting are discussed in terms of surface energies and the disjoining pressure. Characteristics of molecular systems which may lead to these conditions, including the formation of metastable interface structures and commensurate-incommensurate phase transitions, are also discussed. Brief descriptions of some experimental techniques which have been used to study molecular dewetting are given as well. Examples of molecule-on-insulator systems which undergo dewetting are described in some detail, specifically perylene derivatives on alkali halides, C-60 on alkali halides, and the technologically important system of pentacene on SiO2. These examples point to some possible predicting factors for the occurrence of dewetting, most importantly the formation of an interface layer which differs from the bulk crystal structure.
Update: 8-Oct-2009
Title:: Spin chirality and electric polarization in multiferroic compounds RMn2O5 (R = Ho, Er)
Authors:: Wakimoto, S; Kimura, H; Fukunaga, M; Nishihata, K; Takeda, M; Kakurai, K; Noda, Y; Tokura, Y Author Full Names: Wakimoto, Shuichi; Kimura, Hiroyuki; Fukunaga, Mamoru; Nishihata, Keisuke; Takeda, Masayasu; Kakurai, Kazuhisa; Noda, Yukio; Tokura, Yoshinori
Source:: PHYSICA B-CONDENSED MATTER 404 (17): 2513-2516 SEP 1 2009
Abstract:: Polarized neutron diffraction experiments have been performed on multiferroic materials RMn2O5 (R = Ho, Er) under electric fields in the ferroelectric commensurate (CM) and the low-temperature incommensurate (LT-ICM) phases, where the former has the highest electric polarization and the latter has reduced polarization. It is found that, after cooling in electric fields down to the CM phase, the magnetic chirality is proportional to the electric polarization. Also we confirmed that the magnetic chirality can be switched by the polarity of the electric polarization in both the CM and LT-ICM phases. These facts suggest an intimate coupling between the magnetic chirality and the electric polarization. However, upon the transition from the CM to LT-ICM phase, the reduction of the electric polarization is not accompanied by any reduction of the magnetic chirality, implying that the CM and LT-ICM phases contain different mechanisms of the magnetoelectric coupling. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Solid State Polyselenides and Polytellurides: A Large Variety of Se-Se and Te-Te Interactions
Authors:: Graf, C; Assoud, A; Mayasree, O; Kleinke, H Author Full Names: Graf, Christian; Assoud, Abdeljalil; Mayasree, Oottil; Kleinke, Holger
Source:: MOLECULES 14 (9): 3115-3131 SEP 2009
Abstract:: A large variety of different interactions between the chalcogen atoms, Q, occur in the solid state structures of polyselenides and polytellurides, including both molecular and infinite units. The simplest motifs are classical Q(2)(2-) dumbbells and nonlinear Qn(2-) chains (n = 3, 4, 5,..), e. g. found in alkali metal polychalcogenides. In addition, nonclassical so-called hypervalent motifs exist in the form of linear Q(3)(4-) units or within larger units such as Q(4)(4-) and Q(5)(4-). Infinitely extended Q units include zigzag, cis/trans and linear chains, as well as planar and slightly puckered layers. Several of those are susceptible to Peierls distortions, leading to the formation of both commensurate and incommensurate superstructures and anomalies in transport properties, including metal-nonmetal transitions.
Title:: Manganese adlayers on i-Al-Pd-Mn quasicrystal: growth and electronic structure
Authors:: Shukla, AK; Dhaka, RS; D'Souza, SW; Maniraj, M; Barman, SR; Horn, K; Ebert, P; Urban, K; Wu, D; Lograsso, TA Author Full Names: Shukla, A. K.; Dhaka, R. S.; D'Souza, S. W.; Maniraj, M.; Barman, S. R.; Horn, K.; Ebert, Ph; Urban, K.; Wu, D.; Lograsso, T. A.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (40): Art. No. 405005 OCT 7 2009
Abstract:: Pseudomorphic growth of thin elemental metal films is often observed on a variety of crystalline solids. On quasicrystalline surfaces with their complex structure and the absence of translational periodicity, the situation is different since elemental metals do not exhibit quasicrystalline order, and hence the specific interaction between overlayer and substrate is decisive. Here we study the growth of manganese films on an icosahedral i-Al-Pd-Mn alloy with a view to establishing the growth mode and electronic structure. Although we observe an exponential intensity variation of the adlayer and substrate related x-ray photoemission spectroscopy (XPS) peaks, low energy electron diffraction (LEED) shows that Mn adlayers do not exhibit quasicrystallinity. The detailed structure of the Mn 2p core level line reveals considerable electronic structure differences between the quasicrystalline and elemental metal environment. Evidence of a substantial local magnetic moment on the Mn atoms in the overlayer (about 2.8 mu(B)) is obtained from the Mn 3s exchange splitting.
Title:: Pressure-induced disorder in Rb2ZnCl4
Authors:: Machon, D; Grzechnik, A; Friese, K Author Full Names: Machon, Denis; Grzechnik, Andrzej; Friese, Karen
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (40): Art. No. 405405 OCT 7 2009
Abstract:: Rb2ZnCl4 in the normal phase (T = 308-313 K) has been studied under pressure by means of single-crystal x-ray diffraction up to 3.84 GPa and Raman spectroscopy up to 5.9 GPa. No pressure-induced phase transition has been observed but an orientational disorder of the tetrahedra is enhanced with the pressure. At the same time a partial one-dimensional correlation of some chlorine atoms might be favoured at high pressures. Raman spectra in the incommensurate phase (T = 293 K) were collected to higher pressure (24.2 GPa) varying the pressure-transmitting medium. The hydrostaticity during the compression is shown to affect drastically the broadness of the Raman peaks, leading to an amorphous-like spectrum in the least hydrostatic case.
Title:: Crystallographic and electrochemical characteristics of Ti-Zr-Ni-Pd quasicrystalline alloys
Authors:: Liu, BZ; Zhang, YD; Mi, GF; Zhang, Z; Wang, LM Author Full Names: Liu, Baozhong; Zhang, Yude; Mi, Guofa; Zhang, Zhi; Wang, Limin
Source:: INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 34 (16): 6925-6929 Sp. Iss. SI AUG 2009
Abstract:: Ti45Zr35Ni20-xPdx (x = 0, 1, 3, 5 and 7, at%) alloys were prepared by melt-spinning. The phase structure and electrochemical hydrogen storage performances of melt-spun alloys were investigated. The melt-spun alloys were icosahedral quasicrystalline phase, and the quasi-lattice constant increased with increasing x value. The maximum discharge capacity of alloy electrodes increased from 79 mAh/g (x = 0) to 148 mAh/g (x = 7). High-rate dis-chargeability and cycling stability were also enhanced with the increase of Pd content. The improvement in the electrochemical hydrogen storage characteristics may be ascribed to better electrochemical activity and oxidation resistance of Pd than that of Ni. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Title:: Investigation of the New P ' 3-Na0.60VO2 Phase: Structural and Physical Properties
Authors:: Szajwaj, O; Gaudin, E; Weill, F; Darriet, J; Delmas, C Author Full Names: Szajwaj, Olivier; Gaudin, Etienne; Weill, Francois; Darriet, Jacques; Delmas, Claude
Source:: INORGANIC CHEMISTRY 48 (19): 9147-9154 OCT 5 2009
Abstract:: A new layered phase Na0.60VO2 was synthesized by chemical deintercalation of sodium from the pristine compound O3-NaVO2. The Na0.60VO2 compound exhibits a distorted P'3-type oxygen stacking (AABBCC) with an average monoclinic unit cell containing a = 4.9862(14) angstrom, b = 2.8708(8) angstrom, c = 5.917(2) angstrom, and beta = 104.36(3)degrees. A modulated structure was observed by transmission electron microscopy and X-ray diffraction (XRD) measurements. Indexation of the XRD pattern was achieved by using the q vector equal to 0.44b(star), and the 4D superspace group C2/m (0 beta 0) s0 was then deduced. The specific heat measurement showed a strong correlated system with a gamma value of around 20 mJ . mol(-1) . K-2. The electrical conductivity shows a semiconductor-like behavior with an activation energy of 0.52 eV. A paramagnetic behavior of the susceptibility is observed below room temperature with a Curie constant equal to C = 0.076 emu . K-1 . mol(-1) . Oe(-1). To explain this small value, a model of pseudotriangular clusters of vanadium with a random distribution of V3+ and V4+ was considered.
Title:: Phase formation and structures of quasicrystals and approximants in the Zn-Mg-(Ti, Zr, Hf) system
Authors:: Ohhashi, S; Abe, E; Tanaka, M; Tsai, AP Author Full Names: Ohhashi, S.; Abe, E.; Tanaka, M.; Tsai, A. P.
Source:: ACTA MATERIALIA 57 (16): 4727-4735 SEP 2009
Abstract:: The compositional regions for primitive (P) and face-centered (F) icosahedral quasicrystals (iQc) have been determined to be around Zn84Mg9Zr7 and Zn75Mg18Zr6, respectively. A 1/1 approximant of the F-type iQc was found to have a composition around Zn77Mg18Zr5. A similar tendency has been verified for the Zn-Mg-Hf system. No stable iQc was observed in the Zn-Mg-Ti system. High-resolution X-ray measurements performed with synchrotron radiation showed that the stable iQcs are highly ordered and contain less phason disorder. High-angle annular dark field (HAADF) scanning transmission electron microscopy observation of the 1/1 Zn-Mg-Hf approximant effectively revealed the Hf positions in the structure, whose local contrasts can be reasonably interpreted by a structural model where icosahedral and dodecahedral Hf clusters are mutually interpenetrated. Similar appearances of local contrasts were frequently observed in HAADF images of the F-type iQc, indicating that the iQc structure is also build up of icosahedral clusters that are almost identical to those in the 1/1 approximant. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Update: 1-Oct-2009
Title:: Tailoring Thermally Induced Nano-Quasicrystallization and Deformation-Assisted Nanocrystallization for Mechanical Property Improvement in Zr-Al-Ni-Cu-Pd Bulk Metallic Glasses
Authors:: Saida, J; Setyawan, AD; Kato, H; Matsushita, M; Inoue, A Author Full Names: Saida, Junji; Setyawan, Albertus D.; Kato, Hidemi; Matsushita, Mitsuhide; Inoue, Akihisa
Source:: MATERIALS TRANSACTIONS 50 (8): 2079-2086 AUG 2009
Abstract:: The material design tailoring of a synergistic effect of an in-situ nano secondary phase formation and defomation-induced nanocrystallization for improving the mechanical strength and ductility, has been investigated in Zr65Al7.5Ni10Cu17.5-xPdx bulk metallic glasses (BMGs). As-cast Zr65Al7.5Ni10Cu17.5-xPdx (x = 5-17.5) BMGs have significant ductility in compressive deformation, which is attributed to deformation-induced dynamic nanocrystallization. The 10at% Pd-containing BMG with a low volume fraction of the quasicrystalline (QC) phase of less than 6% exhibits increases in strength and Young's modulus, in addition to a remaining plasticity of similar to 5%, compared with the monolithic glassy alloy. Such improvements in the mechanical properties originate from the combination of two effects of in-situ homogenous nano-QC formation and deformation-induced inhomogeneous nanocrystallization. The present method should be regarded as a new technique for the production of BMGs with high strength and good ductility. [doi:10.2320/matertrans.M2009135]
Update: 24-Sep-2009
Title:: Microstructure, surface composition and chemical stability of partly ordered LaTiO2N
Authors:: Logvinovich, D; Bocher, L; Sheptyakov, D; Figi, R; Ebbinghaus, SG; Aguiar, R; Aguirre, MH; Reller, A; Weidenkaff, A Author Full Names: Logvinovich, Dmitry; Bocher, Laura; Sheptyakov, Denis; Figi, Renato; Ebbinghaus, Stefan G.; Aguiar, Rosiana; Aguirre, Myriam H.; Reller, Armin; Weidenkaff, Anke
Source:: SOLID STATE SCIENCES 11 (8): 1513-1519 AUG 2009
Abstract:: LaTiO2N was synthesized in a thermal ammonolysis process of crystalline La2Ti2O7 prepared by conventional solid state reaction or by ammonolysis of a homogeneous amorphous precursor obtained from a soft-chemistry approach. At room temperature slowly cooled LaTiO2N prepared from either precursor crystallizes in space group I (1) over bar and shows a partially ordered anionic arrangement in contrast to a quenched reference sample. The material possesses a complex microstructure represented by twin domains of different types and orientations, as well as incommensurately modulated fragments. The presence of minor C- and N-containing phases such as carbonates, cyanides and nitrates as well as a small amount of a reoxidation intermediate was detected by infrared and Raman spectroscopy. These small amounts of secondary phases can generally influence the results of the O/N content determination of oxynitride compounds when using thermal analysis methods. The formation of such unwanted secondary phases can be avoided by quenching the oxynitride sample or by cooling in inert atmosphere. (C) 2009 Elsevier Masson SAS. All rights reserved.
Title:: Detailed Phase Analysis and Crystal Structure Investigation of a Bi1-xCaxFeO3-x/2 Perovskite-Related Solid Solution Phase and Selected Property Measurements Thereof
Authors:: Schiemer, J; Withers, R; Noren, L; Liu, Y; Bourgeois, L; Stewart, G Author Full Names: Schiemer, Jason; Withers, Ray; Noren, Lasse; Liu, Yun; Bourgeois, Laure; Stewart, Glen
Source:: CHEMISTRY OF MATERIALS 21 (18): 4223-4232 SEP 22 2009
Abstract:: A well-ordered, perovskite-related, (Bi1-xCaxFeO3-x/2)-O-III solid solution phase is synthesized via a rapid liquid phase sintering technique and shown to exist over the composition range similar to 0.20 < x < similar to 0.49. Two phase regions are shown to separate this phase from compositionally narrow end-member (Bi1-xCaxFeO3-x/2)-O-III solid solutions based on rhombohedral BiFeO3 and brownmillerite, Ca2Fe2O5, respectively. The wide range, non-stoichiometric phase is characterized by a well ordered, (in general) incommensurately modulated structure that varies systematically with composition. Mossbauer spectroscopy is used to verify the oxidation state of iron as (III), as well as showing the existence of three separate iron environments across the solid solution field. HRTEM imaging is used to develop a structural model for the phase at one particular composition. The magnetic, dielectric, and impedance properties of this solid solution phase are reported. Magnetic measurements show antiferromagnetic behavior. There is no change in either susceptibility or antiferromagnetic behavior with composition. Attempts at obtaining saturated ferroelectric loops failed due to high intrinsic conductivity. The phase is found to exhibit a low frequency impedance relaxation that is likely due to correlated oxygen vacancy hopping.
Title:: Differential geometry: a natural tool for describing symmetry operations
Authors:: Kocian, P; Schenk, K; Chapuis, G Author Full Names: Kocian, Philippe; Schenk, Kurt; Chapuis, Gervais
Source:: ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 329-341 Part 5 OCT 2009
Abstract:: Differential geometry provides a useful mathematical framework for describing the fundamental concepts in crystallography. The notions of point and associated vector spaces correspond to those of manifold and tangent space at a given point. A space-group operation is a one-to-one map acting on the manifold, whereas a point-group operation is a linear map acting between two tangent spaces of the manifold. Manifold theory proves particularly powerful as a unified formalism describing symmetry operations of conventional as well as modulated crystals without requiring a higher-dimensional space. We show, in particular, that a modulated structure recovers a three-dimensional periodicity in any tangent space and that its point group consists of linear applications. (C) 2009 International Union of Crystallography Printed in Singapore - all rights reserved
Title:: Point substitution processes for decagonal quasi-periodic tilings
Authors:: Fujita, N Author Full Names: Fujita, Nobuhisa
Source:: ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 342-351 Part 5 OCT 2009
Abstract:: A general construction principle for the inflation rules for decagonal quasiperiodic tilings is proposed. The prototiles are confined to be polygons with unit edges. An inflation rule for a tiling is the combination of expansion and division of the tiles, where the expanded tiles can be divided arbitrarily as long as the set of prototiles is maintained. A certain kind of point decoration process turns out to be useful for the identification of possible division rules. The method is capable of generating a broad range of decagonal tilings, many of which are chiral and have atomic surfaces with fractal boundaries. Two new families of decagonal tilings are presented; one is quaternary and the other ternary. The properties of the ternary tilings with rhombic, pentagonal and hexagonal prototiles are investigated in detail. (C) 2009 International Union of Crystallography Printed in Singapore - all rights reserved
Update: 17-Sep-2009
Title:: Symmetry Breaking in Dense Solid Hydrogen: Mechanisms for the Transitions to Phase II and Phase III
Authors:: Toledano, P; Katzke, H; Goncharov, AF; Hemley, RJ Author Full Names: Toledano, Pierre; Katzke, Hannelore; Goncharov, Alexander F.; Hemley, Russell J.
Source:: PHYSICAL REVIEW LETTERS 103 (10): Art. No. 105301 SEP 4 2009
Abstract:: Spectroscopic data for the high-pressure phases of hydrogen together with the topology of the phase diagram provide new insight on the behavior of the material at megabar pressure. Structural mechanisms are proposed for the transitions to phases II and III. These mechanisms include a partially ordered structure (possibly incommensurate) and an ordered isotranslational structure for the two phases, respectively. The analysis supports the existence of an additional phase, isostructural to phase III, with boundary that meets to form a second triple point with phases I and III.
Title:: Aperiodicity, structure, and dynamics in Ni(CN)(2)
Authors:: Goodwin, AL; Dove, MT; Chippindale, AM; Hibble, SJ; Pohl, AH; Hannon, AC Author Full Names: Goodwin, Andrew L.; Dove, Martin T.; Chippindale, Ann M.; Hibble, Simon J.; Pohl, Alexander H.; Hannon, Alex C.
Source:: PHYSICAL REVIEW B 80 (5): Art. No. 054101 AUG 2009
Abstract:: By combining the results of both x-ray diffraction and neutron total-scattering experiments, we show that Ni(CN)(2) exhibits long-range structural order only in two dimensions, with no true periodicity perpendicular to its gridlike layers. Reverse Monte Carlo analysis gives an experimental distinction between M-C and M-N bond lengths in a homometallic cyanide framework and identifies the vibrational modes responsible for anomalous positive and negative thermal expansion in the title compound.
Title:: Origin of Moireacute structures in C-60 on Pb(111) and their effect on molecular energy levels
Authors:: Li, HI; Franke, KJ; Pascual, JI; Bruch, LW; Diehl, RD Author Full Names: Li, H. I.; Franke, K. J.; Pascual, J. I.; Bruch, L. W.; Diehl, R. D.
Source:: PHYSICAL REVIEW B 80 (8): Art. No. 085415 AUG 2009
Abstract:: Low-energy electron diffraction (LEED) indicates that the monolayer structure of C-60 on Pb(111) comprises two coexisting incommensurate structures with nonsymmetry epitaxial rotations near 20 degrees relative to the Pb(111) lattice. These structures are observed in scanning tunneling microscopy (STM) as Moireacute superstructures having periods of about 46 A degrees and 34 A degrees. The Moireacute images and LEED patterns are consistent with two higher-order commensurate (HOC) structures that were identified using the hexagonal number sequence method. These structures are close to predictions from the Novaco-McTague theory of epitaxial rotation, assuming a weakly corrugated substrate potential. As a consequence of the fullerenes within the Moireacute structures having different local environments, the energetic alignment of the molecular resonances is also modulated, with shifts measured by tunneling spectroscopy of up to 20 meV.
Title:: Commensurate lock-in and incommensurate supersolid phases of hard-core bosons on anisotropic triangular lattices
Authors:: Isakov, SV; Chien, HC; Wu, JJ; Chen, YC; Chung, CH; Sengupta, K; Kim, YB Author Full Names: Isakov, Sergei V.; Chien, Hong-Chi; Wu, Jian-Jheng; Chen, Yung-Chung; Chung, Chung-Hou; Sengupta, Krishnendu; Kim, Yong Baek
Source:: EPL 87 (3): Art. No. 36002 AUG 2009
Abstract:: We investigate the interplay between commensurate lock-in and incommensurate supersolid phases of the hard-core bosons at half-filling with anisotropic nearest-neighbor hopping and repulsive interactions on triangular lattice. We use numerical quantum and variational Monte Carlo as well as analytical Schwinger boson mean-field analysis to establish the ground states and phase diagram. It is shown that, for finite-size systems, there exist a series of jumps between different supersolid phases as the anisotropy parameter is changed. The density ordering wave vectors are locked to commensurate values and jump between adjacent supersolids. In the thermodynamic limit, however, the magnitude of these jumps vanishes leading to a continuous set of novel incommensurate supersolid phases. Copyright (C) EPLA, 2009
Update: 10-Sep-2009
Title:: Coupled Magnetic and Ferroelectric Domains in Multiferroic Ni3V2O8
Authors:: Cabrera, I; Kenzelmann, M; Lawes, G; Chen, Y; Chen, WC; Erwin, R; Gentile, TR; Leao, JB; Lynn, JW; Rogado, N; Cava, RJ; Broholm, C Author Full Names: Cabrera, I.; Kenzelmann, M.; Lawes, G.; Chen, Y.; Chen, W. C.; Erwin, R.; Gentile, T. R.; Leao, J. B.; Lynn, J. W.; Rogado, N.; Cava, R. J.; Broholm, C.
Source:: PHYSICAL REVIEW LETTERS 103 (8): Art. No. 087201 AUG 21 2009
Abstract:: Electric control of multiferroic domains is demonstrated through polarized magnetic neutron diffraction. Cooling to the cycloidal multiferroic phase of Ni3V2O8 in an electric field E causes the incommensurate Bragg reflections to become neutron spin polarizing, the sense of neutron polarization reversing with E. Quantitative analysis indicates the E-treated sample has a handedness that can be reversed by E. We further show a close association between cycloidal and ferroelectric domains through E-driven spin and electric polarization hysteresis. We suggest that a definite cycloidal handedness is achieved through magnetoelastically induced Dzyaloshinskii-Moriya interactions.
Title:: Structural transformations and magnetic properties of Bi(1-x)Ln(x)FeO(3) (Ln = La, Nd, Eu) multiferroics
Authors:: Troyanchuk, IO; Bushinsky, MV; Karpinsky, DV; Mantytskaya, OS; Fedotova, VV; Prochnenko, OI Author Full Names: Troyanchuk, I. O.; Bushinsky, M. V.; Karpinsky, D. V.; Mantytskaya, O. S.; Fedotova, V. V.; Prochnenko, O. I.
Source:: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 246 (8): 1901-1907 AUG 2009
Abstract:: Crystal structures of Bi(1-x)Ln(x)FeO(3) systems (Ln = La, Nd, Eu) are studied using X-ray and neutron diffraction, magnetization measurements as well as electron microscopy. It was shown that the unit cell of the Bi1-xLaxFeO3 system is described with the R3c space group in the concentration interval 0 < x < 0.15, with the space group Imma (0.4 < x < 0.5) and with the Puma at x > 0.5. The mixed-phase state was observed in the range 0.15 < x < 0.4 independent of synthesis conditions. A similar sequence of the phase transformations was observed for Bi1-xNdxFeO3 system, In the case of qBi(1-x)Eu(x)FeO(3) series the unit cell is rhombohedral (R3c) at x 0.08 and orthorhombic (Pnma) at x > 0.20, whereas no evidence for Imma phase was found. The magnetization study has revealed the spontaneous magnetization to be associated with Prima and Imma phases that do not allow conventional ferroelectricity, The ferroelectric R3c phase exhibits meta-magnetic behavior due to transition from an incommensurately modulated antiferromagnetic state to a weak ferromagnetic state. Substitution of Bi3+ with Ln(3+) leads to a strong decrease of external magnetic field inducing a metamagnetic transition. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:: Resonant Magnetic X-ray Diffraction Study on the Triangular Lattice Antiferromagnet GdPd2Al3
Authors:: Inami, T; Terada, N; Kitazawa, H; Sakai, O Author Full Names: Inami, Toshiya; Terada, Noriki; Kitazawa, Hideaki; Sakai, Osamu
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (8): Art. No. 084713 AUG 2009
Abstract:: Resonant magnetic x-ray diffraction experiments were carried out on the stacked triangular lattice antiferromagnet GdPd2Al3. The experiments revealed an expected initial collinear c-axis order at T-N1 followed by an additional in-plane order at T-N2, while at the same time we found that the ground state is a helically ordered state of a very long incommensurate period of approximately 700 angstrom. The distribution of K-domains was highly anisotropic, and the domain with the modulation vector normal to the surface of the crystal was ascendant. Low-field magnetization is discussed on the basis of the observed incommensurate magnetic structure.
Title:: Studies of Multiferroic System of LiCu2O2: II. Magnetic Structures of Two Ordered Phases with Incommensurate Modulations
Authors:: Kobayashi, Y; Sato, K; Yasui, Y; Moyoshi, T; Sato, M; Kakurai, K Author Full Names: Kobayashi, Yoshiaki; Sato, Kenji; Yasui, Yukio; Moyoshi, Taketo; Sato, Masatoshi; Kakurai, Kazuhisa
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (8): Art. No. 084721 AUG 2009
Abstract:: Neutron diffraction and Li-7-NMR have been applied to determine the three dimensional magnetic structures of the multiferroic system LiCu2O2, which has four chains (ribbon chains) of edge-sharing CuO4 square planes in a unit cell. First, we have confirmed that there are successive magnetic transitions at T-N1 = 24.5 K and T-N2 = 22.8 K. In the T region between T-N1 and T-N2, the quasi one-dimensional spins (S = 1/2) of Cu2+ ions within a chain have a collinear and sinusoidally modulated structure with Cu-moments parallel to the c-axis and with the modulation vector along the b-axis. At T < T-N2, an ellipsoidal helical spin structure with the incommensurate modulation has been found. We present detailed parameters, describing the modulation amplitudes, helical axis vectors as well as the relative phases of the modulations of four ribbon chains, which can well reproduce both the NMR and neutron results, in the two magnetically ordered phases. This finding of the rather precise magnetic structures enables us to discuss the relationship between the magnetic structure and the multiferroic nature of the present system in zero magnetic field, as presented in our companion paper (paper I), and open a way how to understand the reported electric polarization under the finite magnetic field.
Title:: Evaluation of the local environment for nanoscale quasicrystal formation in Zr80Pt20 glassy alloy using Voronoi analysis
Authors:: Saida, J; Itoh, K; Sato, S; Imafuku, M; Sanada, T; Inoue, A Author Full Names: Saida, Junji; Itoh, Keiji; Sato, Shigeo; Imafuku, Muneyuki; Sanada, Takashi; Inoue, Akihisa
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (37): Art. No. 375104 SEP 16 2009
Abstract:: The local atomic structure of nano-quasicrystal-forming Zr80Pt20 binary glassy alloy was investigated by reverse Monte Carlo modeling based on the results of x-ray diffraction. A prepeak at Q similar to 17 nm(-1) originating from the unique bonding between the Pt-Pt pair is observed in the structure factor. Voronoi analysis indicates that an icosahedral-like polyhedron is formed around Pt. It is also found that icosahedral-like polyhedra exist around Zr; however, the fraction of perfect icosahedra is considerably lower than that in the nano-quasicrystal-forming Zr70Pd30 glassy alloy. A difference in the local environment between the two binary quasicrystal-forming glassy alloys is suggested.
Title:: Direct observation of double-k lattice modulation in double-k magnetic structures. The case of CeAl2
Authors:: Stunault, A; Schweizer, J; Givord, F; Vettier, C; Detlefs, C; Boucherle, JX; Lejay, P Author Full Names: Stunault, A.; Schweizer, J.; Givord, F.; Vettier, C.; Detlefs, C.; Boucherle, J-X; Lejay, P.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (37): Art. No. 376004 SEP 16 2009
Abstract:: Symmetry analysis is combined with x-ray scattering experiments to investigate the lattice modulation associated with the incommensurate magnetic structure in the case of a double-k structure. The expansion of the free energy shows that the components of the magnetic structure with propagation vectors k(1) and k(2) can couple via components of lattice modulations. It is shown that the classical diffraction peaks reflecting a 2k propagation vector, associated with magneto-elastic effects in single-k structures, will coexist with diffraction peaks with propagation vectors k(1) - k(2) or k(1) + k(2). The existence of these latter peaks can be considered as a signature of a double-k magnetic structure. In the case of the double-k modulated structure of CeAl2, group theory is applied directly to the study of the charge modulation. An x-ray scattering study of the 2k satellites shows that the lattice displacements of the two Ce sites of the structure are antiparallel to each other, and perpendicular to the direction of the magnetic modulation. We also confirm experimentally the existence of k(1) + k(2) satellites.
Title:: Formation of Nano-Quasicrystalline Decagonal Phase in the Al70Cu10Co5Ni15 System by High Energy Ball Milling
Authors:: Yadav, TP; Mukhopadhyay, NK; Shaz, MA; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Mukhopadhyay, N. K.; Shaz, M. A.; Tiwari, R. S.; Srivastava, O. N.
Source:: JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 (9): 5527-5532 SEP 2009
Abstract:: A nano decagonal quasicrystalline phase in the Al70Cu10Co5Ni15 alloy has been synthesized by mechanical alloying of a mixture of elemental powders followed by annealing. A high-energy ball milling of the elemental mixture of Al, Cu, Co and Ni leads to the formation of B2 type quaternary intermetallic alloys. The X-ray diffraction and transmission electron microscopy techniques have been employed for characterization of the samples. It was observed that the dissolution of the individual elements into an alloy led to the formation of a nano B2 phase. This phase was found to be quite stable against milling and no other crystalline or amorphous phases could be detected. Milled powder after annealing at 700 degrees C for 60 h was found to transform to nano-decagonal phase. Attempts have been made to understand the evolution of the complex intermetallic nano phases and their relative stability during milling.
Title:: Two Variants of the 1/2[110](p)(203)(p) Crystallographic Shear Structures: The Phasoid Sr0.61Pb0.18(Fe0.75Mn0.25)O-2.29
Authors:: Lepoittevin, C; Hadermann, J; Malo, S; Perez, O; Van Tendeloo, G; Hervieut, M Author Full Names: Lepoittevin, Christophe; Hadermann, Joke; Malo, Sylvie; Perez, Olivier; Van Tendeloo, Gustaaf; Hervieut, Maryvonne
Source:: INORGANIC CHEMISTRY 48 (17): 8257-8262 SEP 7 2009
Abstract:: For the composition (Sr0.61Pb0.18)(Fe0.75Mn0.25)O-2.29, a new modulated crystallographic shear structure, related to perovskite, has been synthesized and structurally characterized by transmission electron microscopy. The structure can be described using a monoclinic supercell with cell parameters a(m) = 27.595(2) angstrom, b(m) = 3.8786(2) angstrom, c(m) = 13.3453(9) angstrom, and beta(m) = 100.126(5)degrees, refined from powder X-ray diffraction data. The incommensurate crystallographic shear phases require an alternative approach using the superspace formalism. This allows a unified description of the incommensurate phases from a monoclinically distorted perovskite unit cell and a modulation wave vector. The structure deduced from the high-resolution transmission electron microscopy and high-angle annular dark-field-scanning transmission electron microscopy images is that of a 1/2[110](p)(203)(p) crystallographic shear structure. The structure follows the concept of a phasoid, with two coexisting variants with the same unit cell. The difference is situated at the translational interface, with the local formation of double (phase 2) or single (phase 1) tunnels, where the Pb cations are likely located.
Title:: Spin density wave dislocation in chromium probed by coherent X-ray diffraction
Authors:: Jacques, VLR; Le Bolloc'h, D; Ravy, S; Giles, C; Livet, F; Wilkins, SB Author Full Names: Jacques, V. L. R.; Le Bolloc'h, D.; Ravy, S.; Giles, C.; Livet, F.; Wilkins, S. B.
Source:: EUROPEAN PHYSICAL JOURNAL B 70 (3): 317-325 AUG 2009
Abstract:: We report on the study of a magnetic dislocation in pure chromium. Coherent X-ray diffraction profiles obtained on the incommensurate Spin Density Wave (SDW) reflection are consistent with the presence of a dislocation of the magnetic order, embedded at a few micrometers from the surface of the sample. Beyond the specific case of magnetic dislocations in chromium, this work may open up a new method for the study of magnetic defects embedded in the bulk.
Title:: Field-dependent competing magnetic ordering in multiferroic Ni3V2O8
Authors:: Singh, AK; Jain, D; Ganesan, V; Nigam, AK; Patnaik, S Author Full Names: Singh, A. K.; Jain, D.; Ganesan, V.; Nigam, A. K.; Patnaik, S.
Source:: EPL 86 (5): Art. No. 57001 JUN 2009
Abstract:: The geometrically frustrated magnet Ni3V2O8 undergoes a series of competing magnetic ordering at low temperatures. Most importantly, one of the incommensurate phases has been reported to develop a ferroelectric correlation caused by spin frustration. Here we report an extensive thermodynamic, dielectric and magnetic study on clean polycrystalline samples of this novel multiferroic compound. Our low-temperature specific heat data at high fields up to 14 Tesla clearly identify the development of a new magnetic-field-induced phase transition below 2 K that shows signatures of simultaneous electric ordering. We also report temperature-and field-dependent dielectric constant that enables us to quantitatively estimate the strength of magnetoelectric coupling in this improper ferroelectric material. Copyright (C) EPLA, 2009
Title:: Theory of magnetic order in Fe1+yTe1-xSex
Authors:: Fang, C; Bernevig, BA; Hu, JP Author Full Names: Fang, Chen; Bernevig, B. Andrei; Hu, Jiangping
Source:: EPL 86 (6): Art. No. 67005 JUN 2009
Abstract:: We develop a local spin model to explain the rich magnetic structures in the ironbased superconductors Fe1+yTe1-xSex. We show that our model exhibits both commensurate antiferromagnetic and incommensurate magnetic order along the crystal a-axis. The transition from the commensurate to the incommensurate phase is induced when the concentration of excess Fe atoms is larger than a critical value. Experimentally measurable spin-wave features are calculated, and the mean-field phase diagram of the model is obtained. Our model also suggests the existence of a large quantum critical region due to strong spin frustration upon increasing Se concentration. Copyright (C) EPLA, 2009
Title:: A "checkerboard" orbital-stripe phase and charge ordering transitions in Pr(SrxCa2-x)Mn2O7 (0 <= x <= 0.45)
Authors:: Li, ZA; Li, X; Wang, Z; Tian, HF; Ma, C; Zeng, LJ; Yang, HX Author Full Names: Li, Z. A.; Li, X.; Wang, Z.; Tian, H. F.; Ma, C.; Zeng, L. J.; Yang, H. X.
Source:: EPL 86 (6): Art. No. 67010 JUN 2009
Abstract:: The charge/orbital ordering (COO) behaviors in the double-layered Pr(SrxCa2-x)Mn2O7 have been investigated by in situ transmission electron microscopy (TEM) observations. The experimental results reveal that two charge ordering (CO) phase transitions, so-called T-co1 and T-co2, commonly exist in the orthorhombic Pr(SrxCa2-x)Mn2O7 (0 <= x <= 0.45) samples. Moreover, a "checkerboard" orbital-stripe phase characterized by two orthogonal COO modulations, q(a) and q(b), is observed between T-co1 and T-co2 in all samples. Detailed TEM investigations on the x=0.2 sample, in which a visible electric polarization was found (Tokunaga Y. et al., Nat. Mater., 5 (2006) 937) demonstrate that the q(b) modulation only survives between T-co1 and T-co2, and the "checkerboard" phase transforms into the conventional one-dimensional COO stripe phase below T-co2. The reversal of in-plane optical anisotropy across the T-co2 transition (Tokunaga Y. et al., Nat. Mater., 5 (2006) 937) is also explained based on TEM result. Copyright (C) EPLA, 2009
Title:: Polygrain icosahedral Al-Pd-Re quasicrystal as a granular electronic conductor
Authors:: Vekilov, YK; Chernikov, MA Author Full Names: Vekilov, Yu. Kh.; Chernikov, M. A.
Source:: EPL 87 (1): Art. No. 17010 JUL 2009
Abstract:: The mechanism of low-temperature electronic transport in polygrain samples of icosahedral Al-Pd-Re is analyzed by analogy with granular electronic systems. The intergranular tunneling and electrostatic energy (Coulomb blockade) are responsible for a specific behaviour of the electrical conductivity in polygrain samples of icosahedral Al-Pd-Re at low temperatures. Depending on the structural state of the sample, both factors may be important and the variable-range hopping regime, of Efros-Shklovskii's type, takes place. For the strong-coupling state the tunneling prevails, and the low-temperature variation of the electrical conductivity is dominated by the Coulomb-interaction and weak-localization corrections. Copyright (C) EPLA, 2009
Title:: Suppression of the current leakage in charge ordered Lu2Fe2Fe1-xMnxO7 (0 < x < 0.86)
Authors:: Qin, YB; Yang, HX; Zhang, Y; Tian, HF; Ma, C; Zeng, LJ; Li, JQ Author Full Names: Qin, Y. B.; Yang, H. X.; Zhang, Y.; Tian, H. F.; Ma, C.; Zeng, L. J.; Li, J. Q.
Source:: APPLIED PHYSICS LETTERS 95 (7): Art. No. 072901 AUG 17 2009
Abstract:: The ferroelectricity, magnetic properties, and charge-ordering modulations in the layered Lu2Fe2Fe1-xMnxO7 have been investigated for x ranging from 0 to 0.86. Experimental measurements reveal that substitution of Mn for Fe could evidently influence the low temperature magnetic transition. Moreover, ferroelectric analysis suggests that introduction of Mn ions in this layered system can efficiently suppress the conducting leakage and result in clear hysteresis loops in the polarization-electric field switching curves. The charge ordering states in Lu2Fe2Fe1-xMnxO7 characterized by two incommensurate modulations has been observed and discussed in association with the local spontaneous polarizations.
Update: 3-Sep-2009
Title:: Rare-earth free wrought-processed magnesium alloy with dispersion of quasicrystal phase
Authors:: Somekawa, H; Osawa, Y; Singh, A; Mukai, T Author Full Names: Somekawa, Hidetoshi; Osawa, Yoshiaki; Singh, Alok; Mukai, Toshiji
Source:: SCRIPTA MATERIALIA 61 (7): 705-708 OCT 2009
Abstract:: Quasicrystal and related phase particles were successfully dispersed in wrought-processed Mg-7.6 wt.% Zn-3.9 wt.% Al alloy with homogeneous and fine-grained structures. This rare-earth-free alloy showed high strength and ductility balance, which was superior to that of the well-known quasicrystal phase dispersed in Mg-Zn-RE alloys, with a weak texture and a reduction of mechanical asymmetry in yield strength. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:: Microstructural characterization of a laser remelted coating of Al91Fe4Cr3Ti2 quasicrystalline alloy
Authors:: Gargarella, P; Almeida, A; Vilar, R; Afonso, CRM; Rios, CT; Bolfarini, C; Botta, WJ; Kiminami, CS Author Full Names: Gargarella, P.; Almeida, A.; Vilar, R.; Afonso, C. R. M.; Rios, C. T.; Bolfarini, C.; Botta, W. J.; Kiminami, C. S.
Source:: SCRIPTA MATERIALIA 61 (7): 709-712 OCT 2009
Abstract:: A bulk sample of Al-Fe-Cr-Ti alloy with adequate composition to form quasicrystalline phases has been surface remelted, using laser processing techniques, to produce a quasicrystalline surface coating. After the laser treatment,

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