bluuebunny/crossref_metadata_2025 huggingface dataset:
STABILIZATION OF Bi(2223) SUPERCONDUCTING PHASE BY VANADIUM OXIDE ADDITION
Authors: SURESH BABU D. , NARSING RAO G. , BROHAN L. , GANNE M.
Published: November 2004

We report on the ac susceptibility, microwave absorption and dc magnetization of Bi 2− x V x Sr 2 Ca 2 Cu 3 O y (nominal composition). The low T c (2212) phase ( T c = 85 K ) dominates in the x = 0 sample with extremly weak flux pinning. In x = 0.4 sample, both flux pinning and volume fraction of the high T c (2223) phase ( T c = 105 K ) were increased. The intragrain critical current density of the sample with x = 0.4 was estimated and found to be comparable with that of Pb doped Bi 2 Sr 2 Ca 2 Cu 3 O y superconductor. The data suggest that addition of V 2 O 5 in Bi 2 Sr 2 Ca 2 Cu 3 O y system increases the volume fraction of the high T c phase. Probable role of vanadium in enhancing the high T c (2223) phase in Bi-V-Sr-Ca-Cu-O system is discussed.
ELECTRONIC STRUCTURE OF YBa2(Cu1−xFex)3O7
Authors: CRISAN V. , VERNES A. , POPESCU V. , DULCA L. , KAPUSI D.
Published: November 2004

The density of states (DOS) at the Fermi level, (EF), for the 123 superconductor doped with iron was computed. The LCAO model hamiltonian and the Haydock recursive method were used. The iron atoms were located only in one of the copper atom positions Cu1 or Cu2 or in both of them with the same probability. The substitution of Fe in Cu1 positions increased the DOS at the Fermi level as x increased but the substitutions in the Cu2 positions had an opposite effect. In both cases the O2 and O3 positions are inequivalent. When the replacement of copper atoms is produced with the same probability in Cu1 and Cu2 positions the DOS at EF decreases as x increases. The DOS at EF and the electron orbital occupation numbers for O2 and O3 have the same behaviour as the lattice parameters, a and b.
ELECTRON-PHONON INTERACTION IN SEMICONDUCTORS WITH UNSTABLE VALENCE
Authors: KIKOIN K. A. , MISHCHENKO A. S.
Published: November 2004

A microscopic theory for the interaction of lattice vibrations with electronic excitations specific to the intermediate valence semiconductors is proposed. The essentially non-local character of the valence shell excitations leads to the additional dispersion of the electron-phonon matrix elements, which give dramatic contribution to the form of longitudinal phonon branches anomalies. This description enlightens both the mechanism of phonon softening in perfect and imperfect lattices, appearance of extra modes in neutron scattering spectra and the nature of valence fluctuations in RE semiconductors. The phonon spectra of integer valence (EuS, SmS(B)) and mixed valence (Sm(Y)S, SmS(G), TmSe, SmB6) semiconductors are calculated within this unified approach.
CALCULATED PHONON DISPERSIONS IN NB USING FASTLY CONVERGENT DENSITY FUNCTIONAL PERTURBATION THEORY
Authors: YU. SAVRASOV S.
Published: November 2004

Density functional linear response approach is developed in the framework of conventional band theory analysis. It is based on the variational solutions of one–electron Schroedinger equations in linear order. Due to incompleteness of the basis sets in band structure calculations large contributions to the standard perturbation theory are shown to exist. These terms disappear only in plane wave pseudopotential calculations. The formulation allows us to avoid the problem of summation over higher–excited states in all cases. The approach in applied to calculate phonon dispersions in Nb and the results are found to be in excellent agreement with experiment.
ELASTIC CONSTANTS OF d TRANSITION ELEMENTS AND d TRANSITION ALLOYS
Authors: SÖDERLIND PER , WILLS JOHN , ERIKSSON OLLE
Published: November 2004

The shear elastic constant, C′, is calculated from first principles for the cubic 4d and 5d transition elements. This study also includes calculations for selected alloys using the virtual crystal approximation. The tetragonal shear constant for these elements and alloys is found to follow a trend which can be related to the calculated crystal structure stabilities. In fact, the trend of C′ behaves roughly as the the trend displayed by the energy difference between the fcc and bcc crystal structures. The theoretical results are generally in ~90% agreement with experiment for the tetragonal shear constant and this implies indirectly that the discrepancy between theory and experiment found for the crystal energies do not lie in the theoretical data.
ELASTIC EFFECTS IN SOME FERROMAGNETIC URANIUM PNICTIDES
Authors: KACZOROWSKI D. , FINSTERBUSCH D. , LÜTHI B.
Published: November 2004

The results of ultrasonic velocity measurements on single-crystalline U 3 P 4, UCuP 2 and UCuAs 2 ferromagnets are presented. For cubic U 3 P 4 the temperature dependence of all three non-zero elastic constants c 11, c 12 and c 44 has been derived. All of them exhibit a strong softening In the vicinity of T C but particularly large effect (~13%) is observed in the case of the shear constant c 12. For tetragonal UCuP 2 and UCuAs 2 the sound propagation along the c-axis has only been studied. In UCuP 2 both the c 33 and c 44 constants show a strong softening near the magnetic phase transition (~ 7%). Much smaller anomalies in elastic constants at T C and an unusual temperature dependence of c 44 In the ferromagnetic region are observed for the arsenide.
AB-INITIO CALCULATION OF CORRELATION EFFECTS IN METALLIC LITHIUM
Authors: HEILINGBRUNNER ANDREA , STOLLHOFF GERNOT
Published: November 2004

We present an ab initio calculation of the correlation effects in metallic lithium. The calculation is carried out based on the use of local operators (Local Ansatz), where correlations are included as corrections to the Hartree-Fock (HF) ground state. We investigate the strength of longer range correlations and their dependance on distance, which allows us to discuss complementary findings to LDA results. The correlation contributions to the binding energy are extracted. The missing longer range correlations can be estimated. Effects of correlations on the bulk modulus, lattice constant and charge fluctuations are analysed.

The structural phases of Li with bcc- and fcc-symmetry are compared.
AB-INITIO MOLECULAR DYNAMICS IN THE FULL-POTENTIAL LMTO METHOD: DERIVATION OF A PRACTICAL FORCE THEOREM
Authors: METHFESSEL M. , VAN SCHILFGAARDE M.
Published: November 2004

A major advance in electronic structure calculations was the combination of local-density techniques with molecular dynamics by Car and Parrinello seven years ago. Unfortunately, application of the Car-Parrinello scheme has been limited essentially to sp materials because only in the plane-wave pseudopotential method forces are trivial to calculate. We present a systematic approach to derive force theorems with desired characteristics within complicated basis sets, which are applicable to all elements of the periodic table equally well. Application to the LMTO basis set yields an accurate force theorem, quite distinct from the Hellman-Feynman form, which is exceptionally insensitive to errors in the trial density. The forces were implemented in a new full-potential LMTO method which is suited to arbitrary geometries. First results for ab-initio molecular dynamics and simulated annealing runs are shown for some random small molecules and small clusters of silver atoms.
PHASE STABILITY AND ELECTRONIC STRUCTURE OF TRANSITION-METAL ALUMINIDES
Authors: CARLSSON A. E.
Published: November 2004

This paper will describe the interplay between the electronic structure and structural energetics in simple, complex, and quasicrystalline Al-transition metal (T) intermetallics. The first example is the L1 2− DO 22 competition in Al 3 T compounds. Ab-initio electronic total-energy calculations reveal surprisingly large structural-energy differences, and show that the phase stability of both stoichiometric and ternary-substituted compounds correlates closely with a quasigap in the electronic density of states (DOS). Secondly, ab-initio calculations for the structural stability of the icosahedrally based Al 12 W structure reveal similar quasigap effects, and provide a simple physical explanation for the stability of the complex aluminide structures. Finally, parametrized tight-binding model calculations for the Al–Mn quasicrystal reveal a large spread in the local Mn DOS behavior, and support a two-site model for the quasicrystal's magnetic behavior.
ANGULARLY-DEPENDENT MANY-ATOM BOND ORDER POTENTIALS WITHIN TIGHT BINDING HÜCKEL THEORY
Authors: AOKI M. , PETTIFOR D. G.
Published: November 2004

Angularly-dependent many-atom potentials for the bond order of saturated or unsaturated bonds are derived within the tight binding (TB) Hückel approximation. These potentials are firmly based on the theorem of linearized many-atom expansion for the bond order, which is novel and gives exact bond order. The explicit angular dependence appears through the moments and interference terms about a bond. Since these potentials give an appropriate description of bonding, they should play an important role in atomistic simulations for semiconductors and transition metals and their compounds. We demonstrate the rapid convergence of the many-atom series for the potentials through some illustrative examples from s bonded elements and d bonded transition metals.
ON THE PHASE STABILITY OF ALKALI METALS UNDER EXTERNAL PRESSURE
Authors: KARAOGLU BEKIR , RAHMAN S. M. MUJIBUR
Published: November 2004

Structural phase stability of certain alkali metals under external pressure is investigated in terms of the pseudopotential and augmented-spherical-waves (ASW) methods. The pair potential trend and the free energy differences between structures — both treated in a second-order pseudopotential theory — are invoked to explain qualitatively some aspects of the stability of the underlying phases at various pressures. Simultaneously, the ASW method is employed to compute the total energies and density-of-states (DOS) at the Fermi level for the phases concerned. The calculated differences in total energies between structures and the DOS curves shade some light in understanding the phase stability of the alkali metals under pressure. The simultaneous application of a perturbative and a nonperturbative treatment on the same footing has brought along some unified concluding remarks in dealing with this particular problem of phase stability.
ELECTRONIC PROPERTIES OF STABLE QUASICRYSTALS CONTAINING TRANSITION ELEMENTS
Authors: MAYOU D. , TRAMBLY DE LAISSARDIERE G. , CYROT-LACKMANN F.
Published: November 2004

A model describing the electronic structure of transition metal atoms in Hume-Rothery alloys and quasicrystals is constructed. We start from the classical Anderson hamiltonian, and add a potential [Formula: see text] that describes the diffraction of conduction electrons by Bragg planes near the Fermi surface. Strong deviation from the virtual bound state is observed for realistic parameters. Furthermore the scattering of the conduction states by the d-orbitals changes the partial density of conduction states. This results in a contribution to the apparent negative valency of transition elements in Hume-Rothery alloys. The results are systematically compared with ab-initio calculations for a series of Hume-Rothery alloys and are in good agreement. The magnetic properties are discussed and it is shown that in a simple Hartree-Fock scheme the Stoner Criterion does not apply to these systems due to the peculiar sp-d hybridization effects. First results taking correlations into account are also discussed.
MAGNETIC PHASE TRANSITIONS IN TRANSITIONAL METAL OXIDES STUDIED WITH PERTURBED ANGULAR CORRELATIONS
Authors: BARTOS A. , WIARDA D. , INGLOT Z. , LIEB K. P. , UHRMACHER M. , WENZEL T.
Published: November 2004

The Perturbed Angular Correlation (PAC) method with radioactive tracer nuclei is well-suited to study the critical behaviour of magnetic hyperfine fields. Here we present the results of PAC measurements with 111 Cd probes, concerning the antiferromagnetic phase transitions in CuO, Co 3 O 4 and MnO. The measured Larmor frequencies were fitted with a Curie-Weiss type temperature dependence ωL (T) /ωL(0) = (1- T/T N)β. In CuO the PAC probe is subject to a high electric field gradient (efg) with the coupling constant νQ = 434(2) MHz and the asymmetry parameter η = 0.42(1). Therefore, combined electric/magnetic hyperfine interaction is observed below T N. Similar to neutron diffraction experiments, a second magnetic transition was observed at T 1 = 213 K . The analysis of the PAC data gave T N = 224(2) K and β = 0.33(1) for T 1 ≤ T ≤ T N. In the spinel Co 3 O 3, the measured critical parameters for 111 Cd at cation sites with tetrahedral oxygen coordination are T N = 39(1) K and β = 0.34(2). This site has a nearly cubic oxygen coordination and therefore a vanishing efg. In Mn 1−x O (defective NaCl structure, x ≤ 0.15), the critical parameters were found to sensitively depend on the annealing conditions. They will be discussed in comparison with those in Fe 1−x O .
SPIN FLUCTUATIONS IN TCo2 STUDIED BY RESISTIVITY AND THERMOPOWER EXPERIMENTS (T = Y, Lu, Sc, Hf, Zr, Ce)
Authors: BARANOV N. , BAUER E. , GRATZ E. , HAUSER R. , MARKOSYAN A. , RESEL R.
Published: November 2004

The temperature dependence of the resistivity and the thermopower in the region from 4.2K up to 1000K for the six isostructural paramagnetic compounds TCo 2 (T=Y, Lu, Sc, Hf, Zr, Ce) is studied. The resistivity ρ (T) follows a T 2 dependence at low temperatures in all these compounds. Plotting the A values into an A vs. γ2 diagram shows that YCo 2, LuCo 2, and ScCo 2 are spinfluctuation systems (A and γ denote the coefficients in ρ (T) = ρ0 + AT 2 and that of the electronic specific heat, respectively) HfCo 2 and ZrCo 2 do not fit into this general tendency in the ( A , γ2)-diagram. The temperature dependent thermopower S(T) in YCo 2, LuCo 2 and ScCo 2 exhibits a pronounced minimum in the low temperature region. These minima are obviously connected with the existence of spin fluctuations (paramagnon-drag). Spin fluctuations in HfCo 2 and ZrCo 2 are less important. This we conclude also from the ten times smaller A-values and the missing minimum in the thermopower at low temperatures.
BONDING NATURE OF INTERCALATION COMPOUNDS M1/3TiS2 (M=TRANSITION-METAL ATOM, SILVER ATOM, ALKALI-METAL ATOM)
Authors: SUZUKI Naoshi , TESHIMA Tatsuya , MOTIZUKI Kazuko
Published: November 2004

Self-consistent LAPW band calculations have been carried out systematically for intercalation compounds M 1/3 TiS 2 (M=transition metal, silver, alkali metal) in order to clarify bonding nature between the guest atoms and the host TiS 2. In transition-metal intercalates the guest 3d states hybridize with the S 3p states as well as the Ti 3d states. As the result covalent bonds are formed between the guest 3d and S 3p states, conserving the covalent bonds between the Ti 3d and S 3p states of the host. In Ag 1/3 TiS 2 the Ag 4d states hybridize strongly with the S 3p state and destroy the host covalent bonds between the Ti 3d and S 3p states. In Li 1/3 TiS 2 and K 1/3 TiS 2 there is little hybridization between the guest 2s or 4s states and the host Ti 3d or S 3p states. Cohesive properties of M 1/3 TiS 2 compounds, including stacking structures of the guest atoms, are discussed on the basis of the total energy calculation.
INFRARED REFLECTIVITY OF ICOSAHEDRAL Al-Cu-Fe AND Al-Mn ALLOYS
Authors: MACKO D. , KASPARKOVA M. , KÖSTER U. , LIU W. , CSANADY A. , BARNA P. B.
Published: November 2004

Infrared reflectivities of a bulk modulated icosahedral Al 64 Cu 22 Fe 14 alloy and of a thin icosahedral Al-Mn film were measured from 20 to 8000 cm -1 at temperatures between 5 and 300 K. Our observations showed several common features in the reflectivities of both samples.
CONNECTION BETWEEN GIANT MAGNETORESISTANCE AND ROUGHNESS IN SPUTTERED Fe/Cr SUPERLATTICES
Authors: KELLY DAVID M. , FULLERTON ERIC E. , PARKER F. T. , GUIMPEL J. , BRUYNSERAEDE Y. , SCHULLER IVAN K.
Published: November 2004

Detailed structural, magnetotransport, magnetization and Mössbauer measurements of sputtered Fe/Cr superlattices are presented. The interfacial roughness of the superlattice can be controlled systematically and reproducibly by sputtering at different Ar pressures. Conversion electron Mössbauer spectroscopy results indicate that the amount of interdiffusion remains constant in the films as the interfacial roughness increases. The results show that roughness enhances the magnetoresistance for all Cr thickness in the range of 10 to 40Å.
MOLECULAR BEAM EPITAXY OF Fe/Cu MULTILAYERED FILMS AND ITS MAGNETOOPTICAL PROPERTIES
Authors: KONONOV V. P. , OVCHINNIKOV S. G. , VASILYEVA E. P. , ZABLUDA V. N. , POPEL V. M. , EDELMAN I. S. , KHUDYAKOV A. E. , BLECHER B. E. , PARSHIN A. S. , STAROVEROVA I. V.
Published: November 2004

Multilayered structures of 10 Fe layers (25 Å each) and 9 layers of Cu (50 Å) have been obtained by MBE technique using a 3-chambers MBE installation "Angara". For comparison Fe film with the thickness d = 250 Å have been prepared. The chemical composition and structure of the films were controlled by X-ray fluorescent analysis, Auger spectroscopy and electron microscopy measurements. Field dependencies of the magnetooptical Faraday effect were measured at different geometries. Spectral dependence of the Faraday effect revealed a maximum at 700 nm wavelength for this multilayered structure.
MAGNETIC ANISOTROPY AND STRUCTURE DEPENDENCE OF THE HYPERFINE FIELD IN Co FILMS AND Co/Re MULTILAYERS
Authors: BARRADAS N. P. , LEAL J. L. , WOLTERS H. , MELO A. A. , SOARES J. C. , da SILVA M. F. , MELO L. V. , FREITAS P. P. , TRINDADE I. , SWINNEN B. , ROTS M.
Published: November 2004

Multilayers of different Co and Re thickness were studied using RBS/ Channeling combined with hyperfine interaction techniques. We observe interface sharpness for film thickness down to a few monolayers. The magnetic hyperfine field corresponds to the well–known bulk hcp value but slightly depends on the layer thickness. Preferential c–axis orientation normal to the film surface is observed together with an uniaxial basal plane magnetic anisotropy and magnetic coupling through Re 0.5nm layer thickness.
4d MAGNETISM?
Authors: DEMANGEAT C. , BOUARAB S. , DREYSSE H.
Published: November 2004

This paper deals with a new and exciting problem: the possible onset of magnetism in 4d-transition-metals adsorbed on a noble-metal substrate. For Pd on Ag(001), the monolayer is found non-magnetic whereas, for thicknesses of the film comprised between 3 and 5, a magnetic moment is present. For Rh on Ag(001), the monolayer is found strongly magnetic whereas, for thicknesses of the film greater than one monolayer, no magnetism is present. Our results for Pd on Ag(001) are in agreement with recent Surface-Magneto-Optical-Kerr effect and Electron-Capture-Spectroscopy displaying no magnetism for the monolayer but ferromagnetism for thicker slabs. Experimentally, Rh on Ag(001) is not a layer by layer growth: interdiffusion and severe islanding are present. Therefore, a more complex calculation, taking into account these growth conditions have to be performed in order to compare with "real systems".
SURFACE STATES OF NICKEL
Authors: CRISAN V. , VERNES A. , DULCA L. , POPESCU V. , KAPUSI D.
Published: November 2004

In the present paper a calculation for the surface states of the 3d transition metals is reported. The scattering method is used in the combined LCAO-OPW representation for the wave functions. The basis set, in the presence of perturbation, is formed by tight-binding orbitals and plane waves. For the unreconstructed (100) surface of Ni, the surface Brillouin zone projected band1 structure and the bound states for the Γ point computed.
AUGER-ELECTRON SPECTROSCOPY AND MAGNETIC PROPERTIES OF Fe-O EPITAXIAL LAYERS
Authors: PARSHIN A. S. , BLEKHER B. E. , ROLYAKOVA K. P.
Published: November 2004

Epitaxial layers of Fe–O with thickness less than 1 µm have been obtained by the method of chemical transport reactions on a MgO substrate. The low energy region of the Auger spectra layers have been investigated. By comparing the Auger spectra with reference iron oxides spectra the layers were assigned to γ- Fe 2 O 3. The quantitative interpretations of experimental temperature dependences of magnetic moment layers in the framework of Neel's model for collinear ferrimagnetism have been obtained.
ZERO—POINT SPIN FLUCTUATION EFFECTS IN ANHARMONIC WEAK ITINERANT ELECTRON MAGNETS
Authors: SOLONTSOV ALEXANDER
Published: November 2004

The spin fluctuation theory of weak itinerant magnets is critically reviewed and is shown to be well established in the weak spin anharmonicity limit. A new self—consistent approach is formulated in terms of the Landau theory of phase transitions to account for zero—point and thermal fluctuations in anharmonic itinerant magnets. The role of spin fluctuations and Fermi excitations in MnSi, Ni3Al and ZrZn2 is discussed using the inelastic neutron scattering experiments.
ON THE THERMODYNAMICAL PROPERTIES IN THE SLAVE BOSON MEAN FIELD THEORY OF HUBBARD MODEL
Authors: ISODA M.
Published: November 2004

The effect of spin polarization in the slave boson mean field theory in the strongly correlated Heavy electron systems is discussed concerning the thermodynamical properties of the Hubbard model. The free energy is evaluated by taking into account the effective reduction of the quantum states due to the exclusion of double occupation in a site through the introduction of the spin-dependent slave boson.

The magnetic susceptibility, calculated as a function of temperature, shows the Fermi liquid property at low temperature and the local moment behaviour with the proper Curie constant at high temperature. The present results, including the temperature dependence of the specific heat, are compared with the previous results without the reduction of quantum states.
CALCULATION OF ELECTRIC FIELD GRADIENT AND CRYSTAL FIELD PARAMETERS IN RARE EARTH METALS
Authors: KURIPLACH J. , NOVÁK P.
Published: November 2004

Electronic structure of hcp rare earth metals Gd, Tb, Dy, Lu and rare-earth-like Y is calculated using the spin-polarized version of the full potential LAPW method. The electric field gradient at the nucleus site is determined from the nonspherical part of the charge density. Crystal field parameters are obtained from the nonspherical components of self-consistent potential. The influence of the state of the 4f-system on the valence and semi-core electrons is investigated.
THE ORDER OF THE NÉEL TRANSITION IN Cr AND DILUTE Cr ALLOYS WITH V AND Re
Authors: FAWCETT ERIC , NOAKES DAVID
Published: November 2004

The weak first-order Néel transition in Cr was explained by Young and Sokoloff (1974) as being associated with the strain-wave second harmonic of the spin-density wave (SDW). Kotani (1975) developed a theory of higher harmonics of the SDW in Cr and its dilute alloys, which indicates an inverse relation between the amplitude of the strain wave and the value of the incommensurability parameter, δ=1−Q, Q being the SDW wave vector. This effect was observed by Iida et al. (1981), who found that the strain-wave amplitude A2/S1 relative to that of the SDW decreases as V is doped into Cr and δ increases, but remains roughly constant in CrMn alloys as δ decreases and the system approaches commensurability. The ratio S3/S1 of the amplitudes of the third harmonic and the fundamental, on the other hand, increases progressively more rapidly as δ decreases. The present work confirms that the magnitude of the first-order step in S1 at the Néel transition is roughly the same in Cr+0.18 at % Re as in pure Cr (Lebech and Mikke 1972), the values of δ at the transition being 0.32 and 0.35, respectively, whereas in Cr+0.2 at % V having δ=0.42 the Néel transition is continuous.
ELECTRONIC SPIN STATES IN CHROMIUM
Authors: KAISER A.B. , OLEŚ A.M.
Published: November 2004

The electronic spin density and its spatial and temporal variation in Cr and its alloys are still not fully understood. The suggestion that Cr is an example of a spin-split metal is not supported by the evidence. Instead, it appears that three rather different types of magnetic moment are required to describe the electronic spin density in Cr: (1) static spin-density-wave moments and associated low-energy spin fluctuations that collapse at high temperatures; (2) higher-energy paramagnetic fluctuations that increase with temperature; and (3) 3d atomic moments formed due to intra-atomic exchange within 1 Å of the atomic centre showing almost no temperature dependence. We suggest further experiments to clarify this picture.
SPIN WAVES IN ANTIFERROMAGNETIC FCT γ-Mn-Ge ALLOYS
Authors: JANKOWSKA-KISIELIŃSKA J. , JAWORSKA E. , MIKKE K. , MILCZAREK J.J.
Published: November 2004

Our earlier studies of magnetic excitations in γ-Mn-Fe, γ-Mn-Ni and γ-Mn-Cu alloys are now extended to the Mn-Ge system. At very low concentrations of Ge (5% and 10% Ge) we expected to achieve a reliable extrapolation to pure γ-Mn which cannot be obtained in the single-crystalline form.
ATOMIC SHORT RANGE ORDER AND SPIN DENSITY WAVE PROPAGATION IN CuMn
Authors: CABLE J.W. , TSUNODA Y.
Published: November 2004

Neutron scattering studies of the atomic short range order (ASRO) and spin density waves (SDW) were carried out for a Cu-35% Mn sample with an unusually high degree of ASRO that develops mostly in a single tetragonal domain. The SDW peaks show a distinctly non-cubic distribution that is readily correlated with the ASRO and which corresponds to the propagation of SDW only in the c plane of the tetragonally based ASRO. The high degree of ASRO and single domain character of this carefully heat-treated sample produces an unusually stable SDW with a higher transition temperature and a larger correlation length than is observed for quenched alloys of the same Mn content. Since SDW stability depends on structural features in the conduction electron susceptibility and on flat, parallel sections of the Fermi surface, these observations suggest that the degree of ASRO and/or the presence of single domain ASRO influences the sharpness of the relevant Fermi surface features in these alloys.
MICROSTRUCTURE AND TEMPERATURE STABILITY OF SINTERED Nd-Dy-Fe-Co-Mo-Al-B MAGNETS
Authors: RODEWALD W. , SCHREY P. , WALL B.
Published: November 2004

Simultaneous additions of Co and Mo or V, respectively, to Nd-Dy-Fe-Al-B alloys improve the temperature stability of sintered magnets. The intrinsic coercivity at 150 ºC amounts to 9 kA/cm for magnets with a Dy-content of 3 at.%. Hence magnets with a load line, B/μoH=−2, may be operated at temperatures up to 200 ºC.

The additions of Mo or of V result in the precipitation of a tetragonal Mo2FeB2 compound, a=0.58 nm, c=0.32 nm, or of a tetragonal V3–xFexB2 compound, x=0.2...1.2, within the (Nd, Dy)2(Fe, Co, A1)14B grains. The dimensions of the precipitates range from 10 to 600 nm. Besides Mo2FeB2- or V3–xFex+B2-grains, respectively, with dimensions up to 10 μm were observed within the Nd-rich constituents. The intrinsic coercivity, however, is determined by nucleation of reversed domains.

The addition of Co results in a partial replacement of the Nd-Fe solid solution by the Nd3Co compound. Corrosion tests revealed, that the corrosion behaviour is not improved significantly and depends much more on the surface treatment.
ENHANCEMENT OF Fe MAGNETIC MOMENTS IN FERROMAGNETIC Fe16B2, Fe16C2, AND Fe16N2
Authors: MIN B.I.
Published: November 2004

In order to investigate electronic and magnetic properties of Fe16X2 (X=B, C, N) ferromagnet, we have performed electronic structure calculations employing the total energy self-consistent local density functional linearized muffin tin orbital (LMTO) band method. Large enhancement of the magnetic moment is observed in FeII and FeIII, which are located farther from X than FeI. This suggests that the local environment plays a very important role in determining Fe magnetic moments in these compounds. Orbital contribution to the magnetic moment in Fe atoms of Fe16N2 is minor, totalof ~0.6 μB in the unit cell. We have obtained the average magnetic moments per Fe atom, 2.30, 2.40, and 2.50 μB, in Fe16B2, Fe16C2, and Fe16N2, respectively.
BAND-STRUCTURE CALCULATION OF THE MAGNETOCRYSTALLINE ANISOTROPY ENERGY OF Fe3N
Authors: SIBERCHICOT B. , VAST N. , MATAR S.
Published: November 2004

The magnetic properties of the ferromagnetic nitride Fe3N were investigated by means of the ASW method where the spin-orbit coupling enters the variational part of the self-consistent loop. The calculations of magnetocrystalline anisotropy energy were done for different values of the angle between magnetization and the c axis of the hexagonal structure. The easy axis of magnetization was found along this c axis. A least-square fit of the results allowed us to determine the relative contributions of first and second order anisotropy constants.
CALCULATION OF DYNAMICAL MAGNETIC SUSCEPTIBILITIES OF TRANSITION METAL ELEMENTS AND ORDERED COMPOUNDS
Authors: McMULLAN G.J.
Published: November 2004

The dynamical magnetic susceptibility χ(q, ω) may be modelled in terms of a band Lindhard function χo(q, ω) and a generalised molecular field parameter λ(q, ω). Comparison of χo(q, ω) calculated within density functional theory and information on χ(q, ω) inferred from neutron scattering data in nearly magnetic metals suggests that at low temperatures it is possible to understand the main features of χ(q, ω) at small ω near the ordering wavevector in terms of the Lindhard function and a qand ω independent molecular field parameter.
ELECTRONIC BAND STRUCTURES OF ANTIFERROMAGNETIC ORDERED ALLOY FePt3
Authors: SUDA T. , SHIRAI M. , MOTIZUKI K.
Published: November 2004

The electronic band structures of an ordered alloy FePt3, having the Cu3Au-type crystal structure, are calculated by using a self-consistent augmented plane wave (APW) method for both non-magnetic (NM) and antiferromagnetic (AF) states. For the NM state, the conduction bands near the Fermi level are hybridized bands which are mainly composed of Fe 3d and Pt 5d orbitals. The Fermi surface shows clearly the nesting feature for the wavevector Q=(π/a, π/a, 0), which would be responsible for the stabilization of the observed AF structure. For the AF state, a large energy splitting of about 4 eV between the spin-up and spin-down bands is found for only Fe 3d states. The magnetic moment at Fe sites is obtained as 3.3µB/Fe, which agrees well with the observed value of 3.3µB/Fe. By comparing the joint densities of states, the difference in optical spectra between the NM and the AF states is clarified.
THE ELECTRONIC BAND STRUCTURES FOR AN ANTIFERROMAGNETIC STATE OF Cu2Sb-TYPE INTERMETALLIC COMPOUND Cr2As
Authors: SHIRAI M. , KAWAMOTO T. , MOTIZUKI K.
Published: November 2004

Electronic band structure calculations are carried out for the antiferromagnetic state of an intermetallic compound Cr2As, having the Cu2Sb-type crystal structure, by using a self-consistent linearized augmented-plane-wave (LAPW) method. The partial density of states (DOS) for Cr (II) 3d states shows a small energy splitting (about 1 eV) between the spin-up and spin-down bands, while that for Cr (I) 3d states hardly shows. The magnetic moments at Cr (I) and Cr (II) sites are evaluated to be 0.33μB and 1.37µB per atom, respectively. These values agree well with the observed values. The calculated DOS shows good correspondence with photoemission and inverse photoemission spectra measured recently.
METAMAGNETISM AND SPIN FLUCTUATIONS IN Co-BASED INTERMETALLIC COMPOUNDS
Authors: GOTO TSUNEAKI , SAKAKIBARA TOSHIRO
Published: November 2004

High field magnetization and susceptibility of Co-based compounds Y(Co1−xA1x)2 are investigated in the paramagnetic region 0≤x≤0.11. In all the region, a sharp metamagnetic transition is observed, while the susceptibility shows a maximum at finite temperature Tmax. The transition field Hc exhibits a positive shift proportional to T2 with temperature. The Hc in the ground state is found to be proportional to Tmax. The experimental results are discussed with a new theory for itinerant electron metamagnetism based on the spin fluctuation model.
CRYSTAL STRUCTURE DISTORTION AND MAGNETIC ORDERING IN THE Nd1-xLuxMn2 SYSTEM
Authors: KIM-NGAN N.H. , GAIDUKOVA I.YU. , MARKOSYAN A.S. , BROMMER P.E. , FRANSE J.J.M.
Published: November 2004

Powder X-ray diffraction and thermal-expansion measurements have been performed on the Nd1−xLuxMn2 system with x values of 0.0, 0.05, 0.10, 0.15, 0.20, 0.30 and 1.0 in the temperature range from 4.2K to 300K. In the Nd-rich compounds (0≤x≤0.15), a monoclinic distortion of the C14 hexagonal structure below TN and a large volume anomaly at TN caused by the appearance of Mn moments are observed, The large crystal distortion is found to decrease with increasing temperature as well as. with increasing Lu concentration. No crystal distortion and no volume anomaly at TN is found in compounds with x≥0.30, in which the long-range magnetic order of the Mn sublattice has dissapeared as evidenced by high-field magnetization measurements. The crystal distortion is explained by a single-ion mechanism of the crystal field acting on the anisotropic 4f-shell of Nd.
MAGNETIC PHASE TRANSITIONS IN Ce(Fe1–xCox)2 SYSTEM
Authors: ALI NAUSHAD , ZHANG XIANFENG
Published: November 2004

Re-entrant magnetic phase transitions in Ce(Fe1–xMx)2 systems (where M=Al, Ru, Co, etc.) are being investigated by various research groups. It has been observed that the system goes from a paramagnetic to ferromagnetic state followed by an almost complete loss of magnetization as the temperature is lowered. We have done systematic experimental measurements of magnetization, ac susceptibility, electrical resistivity, and thermal expansion on the Ce(Fe1–xCox)2 system. It is found that as the temperature is decreased, the system goes from para- to ferro- to antiferro-magnetic phase. The ferro- to antiferro-magnetic phase transition is a first order transition. Our experimental results are consistent with the magnetic phase diagram predictions by Moriya and Usami's theory of strongly interacting itinerant electron systems.
MAGNETIC BEHAVIOUR OF UPdAl, UCuGa AND UCuSn
Authors: TRAN V.H. , TROĆ R.
Published: November 2004

Magnetic susceptibility and electrical resistivity have been measured on UCuGa, UCu1+xSn1−x, (x=0 and 0.1), and UPdAl. The first two compounds, crystallizing in the hexagonal CaIn2-type structure, show at low temperatures an antiferromagnetic ordering probably with complex structures. UPdAl, which adopts the orthorhombic TiNiSi-type structure, was found to be a weakly temperature-dependent paramagnet down to 4.2 K.
SELF-ORGANIZED CRITICALITY AND THE BARKHAUSEN EFFECT IN AMORPHOUS AND POLYCRYSTALLINE METALS
Authors: COTE PAUL J. , MEISEL LAWRENCE V.
Published: November 2004

An investigation of the possibility that the Barkhausen effect in amorphous and polycrystalline ferromagnets is an example of self-organized criticality is described. Since the theory of self-organized criticality was introduced by Bak, Tang, and Weisenfeld to explain the behavior of spatially extended, dissipative, dynamical systems the Barkhausen effect is a natural candidate for such a description. The data are consistent with self-organized critical behavior: the power spectral densities depend on frequency f as 1/fa and the distribution of pulse energies are well described by a power law analogous to the Gutenberg-Richter law for earthquakes. Alternative explanations for power law dependences are also presented.
MAGNETOSTRICTION OF SOFT MAGNETIC NANOCRYSTALLINE Fe-BASED GLASSES WITH Cu, Nb AND Ta ADDITIONS
Authors: ŻUBEREK R. , BARAN M. , KULIK T. , SZYMCZAK H.
Published: November 2004

The magnetostriction constants of three compounds of composition Fe74.5Nb3Si13.5B9, Fe73.5Cu1Nb3Si13.5B9 and Fe73.5Cu1Ta3Si13.5B9 in the as cast state and after heat treatments were measured by a ferromagnetic resonance method at room temperature. Controlled crystallization of the glasses studied was performed in a Perkin-Elmer DSC-2 unit applying continuous heating from room temperature to some maximum temperature, chosen individually for each alloy. It was found that the magnetostriction constants decreased rapidly when the nanocrystalline structure was created.
INFLUENCE OF LOCAL ENVIRONMENT ON THE MAGNETIC MOMENT IN THE TRANSITION METAL ALLOYS
Authors: JEZIERSKI A.
Published: November 2004

We study the dependence of the magnetic moment on the short range ordering in Pt1−cMnc, Pt1−cCrc, Pt1−cCoc andPd1−cCoc alloys. The electronic density of states for the fcc disordered system is calculated by the TB LMTO-CPA method. The magnetic moment is estimated using the Stoner model, We find that the value of the magnetic moment increases with increasing ordering in the system.
ELECTRONIC AND MAGNETIC STUCTURE OF HEXAGONAL FeGe
Authors: HJELM ANDERS
Published: November 2004

Al low temperatures hexagonal FeGe (B 35) exhibits a double—cone antiferromagnetic spin structure. In the present work spin polarized, self consistent band structure calculations are presented for one (ferromagnetic) and two (antiferromagnetic) unit cells. The calculated sublattice magnetization along the c axis, 1.47 μB/Fe atom, is smaller than the experimental values, 1.53–1.78 μB/Fe atom. It is also shown that the easy direction deviates from the c axis, and the cone half angle is estimated to be 12°, in good agreement with the experimental value of 14°.
THREE- AND FOUR-BODY CORRELATION FUNCTIONS FOR THE BLUME-CAPEL MODEL
Authors: BUZANO C. , EVANGELISTA L.R.
Published: November 2004

The Cluster Variation Method (CVM), in its recent formulation using the Moebius Inversion, is applied to study the critical properties of the face-centered-cubic Blume-Capel model in the triangle and tetrahedron approximations. We develop a procedure which preserves the characteristics of Kikuchi’s Natural Iteration Method, moreover reducing considerably the number of involved variables. The resulting phase diagram is compared with that obtained from lower orders of CVM approximation (single-site and pair) and from other methods (series expansions, Monte Carlo, …). The tetrahedron approximation shows a good agreement with these high-precision methods, in particular for the location of the tricritical point. The behavior of order parameters and multisite (up to four-body) correlation functions is determined for all significant regions of the phase space.
CONFIGURATIONAL ENTROPY IN OCTAGONAL TILING MODELS
Authors: MOSSERI RÉMY , BAILLY FRANCIS
Published: November 2004

We calculate the configurational entropy of random tilings obtained by elementary flips from a perfect octagonal tiling with an octagonal boundary. We map the problem of generating all configurations onto a partition problem. We calculate numerically the number of configurations and the associated entropy. We give some exact expressions in restricted cases and upper bounds for the entropy in the asymptotic case.
PERFECT MATCHING RULES FOR UNDECORATED TRIANGULAR TILINGS WITH 10-, 12-, AND 8-FOLD SYMMETRY
Authors: KLITZING RICHARD , SCHLOTTMANN MARTIN , BAAKE MICHAEL
Published: November 2004

Perfect matching rules are derived for quasiperiodic triangular tilings with 10-, 12-, and 8-fold symmetry. We use the composition/decomposition approach via local inflation/deflation symmetry and emphasize the locality of our procedure: The matching rules given here are formulated using certain decorations of the tilings. These decorations turn out to be redundant, i.e., they are locally derivable from the undecorated tilings. Hence, the latter are determined by perfect matching rules as well.
THE PHONON SPECTRUM OF THE OCTAGONAL TILING
Authors: LOS J. , JANSSEN T. , GÄHLER F.
Published: November 2004

A study of the phonon spectrum of the octagonal tiling is presented, by calculating and analysing the properties of the spectrum of perfect and randomized commensurate approximants with unit cells containing up to 8119 vertices. The total density of states, obtained by numerical integration over the Brillouin zone, exhibits much structure, and in the low frequency range of the spectrum there is deviation from the normal linear behaviour in the form of pseudogaps. For randomized approximants these pseudogaps disappear and the density of states is globally smoothened. It turns out that the widths of the gaps in the dispersion vanish in the low frequency limit. Therefore the scaling behaviour of the lowest branches tends to the behaviour of an absolutely continuous spectrum, which is not the case at higher frequencies. As an application, the vibrational specific heat of the different tiling models is calculated and compared to the specific heat of a square lattice and of a Debye model.
DEGENERATE COHERENT BOND STATES
Authors: CHAKRABARTI J.
Published: November 2004

When the global number of carriers fluctuates a set of spin-singlet soliton states become exact solutions of the hopping hamiltonian. The issue of degeneracy of these states has received insufficient attention and is addressed here at length. The elementary excitations on these coherent states are analysed. The dispersions over these solitons show that they may emerge close to nested fermi surfaces when the CDW or the SDW instability for some reason is suppressed.
MEAN FLOW OF A VERTICALLY VIBRATED HOURGLASS
Authors: EVESQUE Pierre , MEFTAH Wahib
Published: November 2004

We have investigated the mean flow of a hourglass submitted to vertical vibrations as function of the amplitude a and frequency f=Ω/2π of the vibration (5Hz≤f≤100Hz) . We find that the time constant of the flow dynamics is longer than 0.2s, that the flow rate is weakly sensitive to vibrations as far as these ones have a small enough amplitude (aΩ2<g=10m/s2) . When aΩ2 becomes larger than g and when the frequency is located inside a resonance domain (10Hz<f<80Hz) , the flow rate decreases strongly; it even stops at large aΩ2 and when 40Hz<f<60Hz .
FLUIDIZATION, CONDENSATION AND CLUSTERIZATION OF A VIBRATING COLUMN OF BEADS
Authors: CLÉMENT E. , LUDING S. , BLUMEN A. , RAJCHENBACH J. , DURAN J.
Published: November 2004

We present numerical and experimental results for the response under external vibration of one-dimensional columns of beads. Such systems are toy-models for dissipative granular materials. We show that a simple algorithm is able to reproduce the basic experimental features. Our main result is that an increase in acceleration leads to a transition from a condensed to a fluidized state of the columns. We discuss this cross-over acceleration as a function of the number of beads and of the restitution coefficient (dissipation) per collision. Also, we show that at high dissipation level clustered states (where all the beads are in contact) exist. The algorithm used by us reproduces well this cluster dynamics.
NUMERICAL MODELING OF VIBRATED BEDS
Authors: TAGUCHI Y-h.
Published: November 2004

I propose a numerical model which describes the dynamical features of vibrated beds. It succeeds in reproducing convective motion in vibrated beds which was observed by Faraday for the first time in 1831. In addition to this, this modeling can explain threshold value of instability and surface fluidization. Moreover, I numerically show vibrated bed without side wall can exhibit strong non-linear feature like turbulence or anomalous diffusion.
DYNAMIC MODEL FOR GRANULAR ASSEMBLY
Authors: HONG DANIEL C.
Published: November 2004

In this paper, we investigate in detail the complex dynamics and flow patterns of granular materials based on two simple yet quite realistic models: the diffusing void model and the nonlinear dynamic model. We first show how the diffusing void model describes some of the unusual and unique features of granular flows in a confined geometry such as the deformation of the free surface, the formation of dead zones, the flow around obstacles, the shock front with its companion void regions, and the front profile of the propagating density waves. We then provide theoretical framework for the diffusing void model by deriving it from the continuity equation and the microscopic force balance equation. This approach shows how the nonlinear term arises naturally, leading to the nonlinear dynamic equation, whose numerical solutions do exhibit the features shown by the diffusing void model and the experiment. When nonlocal interaction between grains is taken into account, the mass term appears in the dynamic equation in the thermodynamic limit, leading to exponential decay of the granular pile. This might account fot the different behaviors for large and small granular piles. We also present exact results of the stress distribution of a hexagonally packed granular pile in two dimensions and show that the load acting on each grain at the bottom layer is identical. We also present the results of molecular dynamics simulations which show that the speed of the outgoing grains in a hopper is independent of the depth. We then outline a few outstanding problems that are technologically important, yet can be handled by the models proposed and developed in this paper.
COMPUTATIONAL MODELS FOR SAND RIPPLE AND SAND DUNE FORMATION
Authors: NISHIMORI HIRAKU , OUCHI NORIYUKI
Published: November 2004

Computational models for sand ripple and sand dune dynamics are proposed. From the results of the simulations, with the simple analysis of these models, we give the quantitative explanation for sand ripple formation and that for the origin of the rich variety of sand dunes’ shape.
GRANULAR FLOW SIMULATION FOR METAL INJECTION MOLDING PROCESS
Authors: IWAI TAKASHI , AIZAWA TATSUHIKO , KIHARA JUNJI
Published: November 2004

Metal Injection Molding treats the complex fluid which consists of thermoplastic tic polymer medium and dense metallic powder suspensions to improve flowability and formability. To understand its fundamental mechanical behavior, it is important to consider powder structures and mechanics precisely. For the analysis of this process, a new granular model is proposed, which is based on the Distinct. Element Method. Each element in this method is constituted by combining a metal powder with a binder (polymer) shell surrounding it. Both elasticity and viscosity for powder particles and binders are only considered in this mixture model as the constitutive relations. Several numerical results have demonstrated the effectiveness and validity of our developed granular modeling to deal with the various phenomena appearing in MIM process.
SIMULATION OF ELECTRO-RHEOLOGICAL FLUIDS WITH WATER CAPILLARY FORCES
Authors: Tamura H. , See H. , Doi M.
Published: November 2004

It is known that the viscosity of certain Electro-Rheological Fluids depends on the amount of water in the dispersed particles. One explanation is the adhesion between contacting particles due to the capillary force of water. In this work we investigate by computer simulations how the aggregate structure and shear stress depend on the water capillary force. From our simulation we found that when the capillary force becomes larger, the shear resistance increases and the aggregates’ shape changes from chain-like to compact.
THE LOCK-IN TRANSITION OF VORTICES IN LAYERED SUPERCONDUCTORS
Authors: FEINBERG D. , ETTOUHAMI A.M.
Published: November 2004

A review of the theory of the lock-in transition of vortices onto the layer direction in type II layered superconductors is presented. This phenomenon originates from the lowering of free energy when vortex cores are centered between adjacent layers. The approaches for the low-temperature “quasi-2D" as well as the 3D anisotropic regimes are reviewed. variational method. The phenomenological model with a modulated vortex core is shown In particular, the temperature variation of the core energy modulation is obtained by a to work in all the temperature range. The behaviour of the reversible torque is described as a function of the various parameters: field, temperature, anisotropy, and the existence of the London maximum is discussed. A simple interpretation of the transition is given as well as the influence of demagnetizing fields.