bluuebunny/crossref_metadata_2025 huggingface dataset:
OPTICAL CONDUCTIVITY AND NUCLEAR RELAXATION RATE IN LAYERED N/S STRUCTURES
Authors: BUZDIN A. I. , KELLER J. , KUPTSOV D. A.
Published: November 2004

Optical conductivity and nuclear relaxation rate are calculated in a model of HTSC in which superconducting (S) and normal layers (e.g. CuO chains in YBa2Cu3O7) alternate assuming that s-wave pairing is present only in the S layers. Our model predicts unusual frequency dependence of the dynamical conductivity and the absence of the peak in the nuclear relaxation rate near Tc.
COMPLEX CONDUCTIVITY IN THIN FILMS OF YBa2Cu3O7 AND YBa2(Cu1−xMx)3O7 WITH M = Zn AND Ni
Authors: LUNKENHEIMER P. , LOIDL A. , TOMÉ-ROSA C. , WAGNER P. , ADRIAN H.
Published: November 2004

Detailed measurements of the complex conductivity σ* = σ′ + i σ″ have been performed in doped and undoped YBa 2 Cu 3 O 7 thin films, for frequencies 1 kHz ≤ ν ≤ 1 GHz and temperatures 10 K ≤ T ≤ 300 K . A peak in σ′ ( T ) shows up just below T c . Such a peak in σ′ ( T ) of high- T c -superconductors has recently been observed at microwave frequencies and has been interpret as the so-called "coherence peak", predicted by the BCS-theory. Our measurements show, for the first time, the frequency dependence of the coherence-like peak. From our results we conclude that the observed peak cannot be explained by coherence effects.
FABRICATION AND CHARACTERIZATION OF SUPERCONDUCTING (BI,PB)-SR-CA-CU-O THICK FILMS ON SR-CA-CU-O SUBSTRATES
Authors: MARX DAVID T. , ALI NAUSHAD
Published: November 2004

We have used a new technique to prepare thick films (about 1 µm) of the Bi(Pb)-based hightemperature superconductors. The method begins by standard powder synthesis of the substrateusing strontium and calcium carbonates and copper oxide in the nominal ratio 3:3:4. Pb may beintroduced into the sample by adding lead oxide. The material is fired in air to 975°C for 24 hourswith one intermediate grinding and pressing of pellets. Bi metal is evaporated onto the surface ofthe pellet. Patterning may be easily accomplished using metal masking. The film is then heattreated in air. Subsequent characterization using resistivity, dc magnetization, x-ray diffraction,and scanning electron microscopy has been performed.
ELECTRON-PHONON INTERACTION AND SUPERCONDUCTIVITY IN OXIDE SUPERCONDUCTORS La2−xSrxCuO4
Authors: SHIRAI M. , KINOSHITA T. , MOTIZUKI K.
Published: November 2004

Effects of electron-phonon interaction on lattice dynamics in oxide superconductors La 2−x Sr x CuO 4 (LSC) are studied microscopically on the basis of the tight-binding band fitted to the first principle band. Breathing-type vibrations of oxygen atoms in the CuO 2 plane are renormalized significantly at around (π/a, π/a, 0) and (π/a, 0, 0) due to strong dependences of the electron-phonon interaction on wavevectors and phonon modes. In the framework of the usual phonon-mediated pairing mechanism, superconducting properties, such as transition temperatures and tunneling spectra, are studied by solving isotropic Eliashberg equations. The spectral function α2F(ω) has a characteristic structure over a wide energy range below 85 meV. The tunneling conductance d I/ d V and its derivative d 2I/ d V2 calculated have prominent peaks below 40 meV, which show good correspondences to those observed by recent tunneling experiments.
ELECTRON-PHONON INTERACTION, LATTICE DYNAMICS AND SUPERCONDUCTIVITY OF LAYERED TRANSITION-METAL DICHALCOGENIDE NbS2
Authors: NISHIO Yoshimasa , SHIRAI Masafumi , SUZUKI Naoshi , MOTIZUKI Kazuko
Published: November 2004

Lattice dynamics of NbX 2( X = S , Se ) is studied by taking account of electron-phonon interaction derived microscopically on the basis of the realistic tight-binding bands fitted to the first-principle bands of NbX 2. Remarkable frequency renormalization of Σ1 phonon mode around [Formula: see text] is caused due to characteristic wave-vector and mode dependences of the electron-phonon interaction as well as nesting effect of Fermi surface. It is also shown that the short range force constant for neighboring X ions on different X-layers in the same X-Nb-X sandwich determines primarily whether lattice instability occurs ( NbSe 2 case) or does not occur ( NbS 2 case). By using the electron-phonon interaction and the lattice dynamics obtained for NbS 2 we have calculated the spectral function α2F(ω) and determined superconducting transition temperature T c by solving the linearlized Eliashberg equation. Renormalization of phonon frequencies due to the eletron-phonon interaction raises considerably the transition temperature and the obtained value of T c agrees in order of magnitude with the experimental data.
ELECTRONIC TRANSPORT PROPERTIES FOR THE ULTRAPURE SINGLE CRYSTALS OF THE TRANSITION METALS UNDER CONDITIONS OF THE STRONG STATIC SKIN EFFECT AT HIGH CURRENT DENSITIES
Authors: STARTSEV V. E. , MARCHENKOV V. V. , CHEREPANOV A. N.
Published: November 2004

The electronic transport properties for the ultrapure single crystals of the transition metals are examined under conditions of the strong electron-surface scattering. In this case the static skin effect can be observed. Under these conditions some anomalies in the electronic properties take place. They are the gigantic growth of the magnetoresistivity with magnetic field increase, the strong dependence of the magnetoresistivity and Hall voltage on the electron-surface interaction, the appearance of the nonlinear current-voltage characteristics in metals. Some cryogenic devices based on the peculiarities of the electronic properties of the ultrapure metal crystals can be created.
THEORY OF ORBITAL SPLITTING IN METALS
Authors: SEVERIN LUKAS , BROOKS M. S. S. , JOHANSSON BÖRJE
Published: November 2004

A theory for orbital splitting is derived from a statistical Hartree-Fock (HF) treatment of open shell interactions. In a scaling procedure, where the HF spinpolarization matrix is replaced by the corresponding local spin density matrix, an expression for the orbital splitting is derived which is well suited for implementation in the standard ab initio calculational scheme. Results for Co metal as well as for the itinerant 5f ferromagnet US is presented, which are in good agreement with experiment.
CALCULATIONS OF THE ZEEMAN SPLITTING FOR PLATINUM GROUP METALS AND NOBLE METALS
Authors: HJELM ANDERS
Published: November 2004

The electronic structures for Rh, Pd, Ir, Pt, Cu, Ag and Au are calculated including the effects of an external magnetic field, using the LMTO — ASA method. The field is included self consistently by adding the Zeeman term to the Hamiltonian in the variational step. The Zeeman splitting of cyclotron orbits on the Fermi surface as well as bulk susceptibilities are calculated for various exchange — correlation potentials. For the platinum group metals good agreement with experiments is found but for the noble metals effects creating orbital magnetism are exaggerated and the calculated susceptibilities as well as the cyclotron orbit Zeeman splitting are larger than the experimental data.
IS THERE A METAMAGNETIC PHASE TRANSITION IN Pd?
Authors: HJELM ANDERS
Published: November 2004

Electronic structure calculations for Pd in external magnetic fields are presented. The external magnetic field is included self consistently by adding the Zeeman term to the variational step. Thereby the Zeeman splitting interacts with the exchange — correlation potential and the spin — orbit coupling. As Pd is on the border of ferromagnetism, calculations of the magnetization as a function of applied field are presented for a variety of exchange — correlation potentials and orbital effects, as well as for expanded crystals. At the experimental lattice constant no phase transition is found.
PHASE DIAGRAMS AND BAND STRUCTURE OF TRANSITION METAL COMPOUNDS
Authors: GRIMVALL GÖRAN , HÄGLUND JAN , GUILLERMET ARMANDO FERNÁNDEZ
Published: November 2004

Phase diagrams and phase stabilities have in the past been dealt with using different approaches. In the Calphad method one seeks a description of the Gibbs energy function G(T) which is accurate enough to be used in calculations of phase diagrams for complex alloys. Ab initio electron band structure calculations, on the other hand, have been used to predict the cohesive properties of solids but such calculations are usually restricted to 0 K. We have combined these methods to get a better understanding of the phase stabilities. In particular we have critically analysed available thermodynamic information and used that together with band structure calculations to systematically discuss trends in the cohesive energy at 0 K and in the vibrational entropy. We have considered transition-metal carbides and nitrides, both in the NaCl and in more complex structures, and also transition-metal diborides.
QUASICRYSTALS: STRUCTURE AND PROPERTIES
Authors: JANOT Christian
Published: November 2004

Quasiperiodic structures can be described as physical irrational cut of structures which are periodic in higher dimensional spaces. Such a so-called quasicrystallography approach has been applied to several real quasicrystals. The Fourier components of these structures are densely distributed in the reciprocal space. This is at the origin of physical properties which may sound ackward for metallic systems. For instance, the electrical resistivity reaches very large values.
TEMPERATURE-DEPENDENT ELECTRONIC STRUCTURE AND MAGNETIC BEHAVIOUR OF MOTT INSULATORS
Authors: NOLTING W. , HAUNERT L. , BORSTEL G.
Published: November 2004

The temperature-dependent electronic and magnetic properties of transition metal monoxides are calculated by use of a theoretical model which takes into account strong 3d Coulomb correlations and 2p-3d hybridization.
ON THE ELECTRONIC STRUCTURE OF CrO2: NEW EXPERIMENTS AND THEORY
Authors: BRÄNDLE H. , WELLER D. , SCOTT J. C. , STICHT J. , OPPENEER P. M. , GÜNTHERODT G.
Published: November 2004

Spectroscopic investigations of the optical constants n and k and the magneto-optical polar Kerr effects θK and εK were used to deterimine the diagonal and off-diagonal conductivity tensor elements of CrO 2 in the energy range 0.8-5eV. The data can be readily explained on the basis of self-consistent spin-polarized bandstructure calculations. A direct comparison of the measured and calculated diagonal optical conductivity is presented for the first time, which can be viewed as experimental confirmation of the ab initio calculated bandstructure of CrO 2.
RESONANT PHOTOEMISSION AT THE LIII THRESHOLD IN CuO
Authors: LÓPEZ M. F. , HÖHR A. , LAUBSCHAT C. , DOMKE M. , KAINDL G.
Published: November 2004

We report on a resonant photoemission study of CuO at the LIII soft-x-ray absorption threshold. The valence-band spectra exhibit a strong enhancement of electron emission at resonance, which is shown to be due to an incoherent superposition of a strong signal from an L3M4,5M4,5 Coster Kronig decay of the core-ionized state and a much weaker photoemission signal. This finding is in strong contrast to the recent claim of a giant Fano-type photoemission resonance in this system.
INVARIANCE OF THE MOBILITY EDGE IN ANODIC TITANIUM OXIDES
Authors: TIT NACIR , HALLEY J. W. , SHORE H. B.
Published: November 2004

We present a theoretical investigation to explain the electronic and optical properties of anodic rutile TiO2 thin films of different thicknesses (ranging from 5nm to 20nm). There is experimental evidence that the observed gap state at 0.7eV below the edge of conduction-band is due to an oxygen vacancy. For this reason, oxygen vacancies are used as defects in our model. A comparison of the calculated bulk-photoconductivity to photospectroscopy experiment reveals that the films have bulk-like transport properties with a bandgap Eg = 3.0eV. On the other hand, a fit of the surface density of states to the scanning tunneling microscopy (STM) experiment on the (001) surfaces has suggested a surface defect density of 5% of oxygen vacancies. To resolve this discrepancy, we calculated the dc-conductivity where localization effects are included. Our results show an impurity band formation at about pc = 9% of oxygen vacancies. We concluded that the studied films have defect densities below the threshold of impurity band formation. As a consequence the gap states seen in STM are localized (i.e: the oxygen vacancies are playing the role of trapping centers, deep levels) and the mobility edge is invariant.
SPECIFIC HEAT OF ErNi5 AND DyNi5
Authors: RADWAŃSKI R. J. , KIM-NGAN N. H. , KAYZEL F. E. , FRANSE J. J. M.
Published: November 2004

The specific heat of DyNi 5 measured on a single-crystalline specimen in the temperature interval from 1.5 K to 250 K has been analyzed in terms of two electronic subsystems. The conduction-electron subsystem is characterized by a value of the Sommerfeld coefficient γ of 36 mJ/K 2 mol . The contribution of the rare-earth subsystem to the specific heat shows a λ-type of peak at T c and above T c a Schottky-type of peak. The rare-earth contribution is well described within a single-ion Hamiltonian that includes the CEF and exchange interactions of the R 3+ ions. The CEF interactions in ErNi 5 and DyNi 5 have been compared and a very similar charge multipolar distribution around the R 3+ ions is found. The energy level scheme of these Kramers ions with J = 15/2 is derived.
ANOMALOUS LATTICE PROPERTIES OF ZrNiSn CAUSED BY ELECTRON LOCALIZATION
Authors: ALIEV F. G. , PRYADUN V. V. , VILLAR R. , VIEIRA S. , CALLEJA J. M. , MESTRES N. , SCOLOZDRA R. V.
Published: November 2004

Thermal transport (resistivity, Seebeck coefficient, thermal conductivity), thermal expansion and Raman spectra of the intermetallic ordered vacancy compound ZrNiSn was studied. Below T = 100 K an isostructural phase transition was observed. Analyzing ZrNiSn properties, we conclude that this transition is related to freezing of Ni atoms in some of equivalent positions. Conduction electrons, delocalized by increasing order at T < 100 K , show a new localization below 20K. In this range, an anomalous negative thermal expansion, possibly caused by electron-electron interaction was seen.
MAGNETO-OPTIC CHARACTERIZATIONS OF SUPERLATTICES AND WEDGED SANDWICHES WITH OSCILLATORY INTERLAYER MAGNETIC COUPLING
Authors: BADER S. D.
Published: November 2004

Three examples of magnetic coupling across metallic spacer layers are considered. Fe/Nb sputtered superlattices are observed to have as many as five antiferromagnetic oscillations, but a weak magnetoresistive anomaly. Epitaxial trilayers of Fe/Mo/Fe grown on Mo(100) and Co/Cu/Co grown on Cu(100) are observed to have short- and long-period oscillations, respectively. The trilayers are grown with wedged spacer layers and characterized in-situ by means of the magneto-optic Kerr effect.
THEORIES OF LONG RANGE OSCILLATORY EXCHANGE COUPLING IN MAGNETIC MULTILAYERS
Authors: HERMAN F. , VAN SCHILFGAARDE M. , STICHT J.
Published: November 2004

In the first part of this paper we present a critical review of recent theoretical studies of long range oscillatory coupling in magnetic multilayers. In the second part we discuss our recent first-principles self-consistent spin-polarized total energy calculations for fcc Co/Cu multilayers. In contrast to simplified theories, our studies take proper account of structural and chemical effects arising from the presence of the Co slabs, as well as their magnetic effects. Using local spin density functional theory and collinear spin arrangements, we obtain long- as well as short-period oscillatory behavior. We also demonstrate that the oscillatory components are strongly dependent on interfacial orientation. The multiperiodicity and orientation dependence can be interpreted in terms of the topology of the bulk Cu Fermi surface. In spite of the limited range of Cu spacer thicknesses examined, we are able to make rough estimates of oscillatory periods; these are in reasonable agreement with experiment.
PROPERTIES OF MBE-GROWN SUPERLATTICES AND ULTRA-THIN FILMS
Authors: FALCO CHARLES M. , ENGEL BRAD N.
Published: November 2004

We have used Molecular Beam Epitaxy (MBE) to grow single-crystal Co/Pd superlattices and Co/TM (TM=Cu, Pd, Ag) bilayers and sandwiches along the three high-symmetry crystal directions; [001], [110], and [111]. In the case of Co/Pd superlattices, we previously reported from x-ray diffraction measurements that for small Co thicknesses the (001) oriented superlattices are coherently strained in-plane to near the bulk Pd lattice spacing. This strain leads to a very large in-plane magnetoelastic volume anisotropy for these superlattices. Here we report quantitative in situ RHEED measurements of Co deposited on Pd (001) that confirm this coherently strained growth. We have also used in situ polar Kerr ellipticity measurements to study the perpendicular magnetic behavior of Pd/Co/TM (111) sandwich structures, where TM is the non-magnetic transition metal overlayer Ag, Cu or Pd. We observed perpendicular loops with coercive fields of H c ≤ 200 Oe for the uncovered Co films for t co ≤ 6 Å, becoming in-plane above this thickness. However, subsequent deposition of just one atomic layer (≈ 2 Å) of any of the TM over the Co resulted in strongly perpendicular, square hysteresis curves with H c ≥ 900 Oe for all films in the Co thickness range studied.
SPIN SPLITTING IN A TWO DIMENSIONAL ELECTRON SYSTEM DETERMINED BY NUCLEAR MAGNETIC RELAXATION AND MAGNETOTRANSPORT ACTIVATION MEASUREMENTS
Authors: BERG A. , WEISS D. , KLITZING K. V. , NÖTZEL R.
Published: November 2004

The spin splitting observed in two-dimensional electron systems at high magnetic fields is not only determined by the single-electron Zeeman energy but also by many-particle effects. Electron-electron interaction results in an enhanced g-factor which can be described by the exchange part of the Coulomb interaction. Nuclear spin lattice relaxation experiments analysing the Overhauser Shift in Electron Spin Resonance (ESR) measurements reveal that the exchange term is dominant. The spin splitting is strongly dependent on magnetic field and temperature. Numerical simulations enable the quantitative determination of the exchange part of the spin split energy. Transport activation measurements verify that the exchange part is proportional to the spin polarization of the electrons.
MAGNETISM OF 4d TRANSITION METAL MONOLAYERS
Authors: KLEINMAN LEONARD
Published: November 2004

After motivating the reasons for performing these calculations, we discuss the various methods of calculation that are used, describe our results for freestanding and epitaxial monolayers of Mo, Pd and Rh and compare with the results of other workers on these and related systems. All calculations agree that a monolayer of Rh on Ag(001) or Au(001) should be ferromagnetic; we conclude by speculating on why experiments disagree.
THE 2-d HEISENBERG MODEL WITH VARIOUS TYPES OF INTERACTIONS: TEMPERATURE DEPENDENCE OF MAGNETIC PARAMETERS AND THE PHASE TRANSITION TEMPERATURE
Authors: GARCIA N. , LEVANYUK A. , SERENA P.
Published: November 2004

Using the low-temperature perturbation (spin wave) theory we calculate the temperature dependence of anisotropy constant, spin-wave stiffness, spontaneous magnetization for a two-dimensional ferromagnetic Heisenberg model with various types of anisotropy and interactions. We found that the Polyakov renormalization procedure is inapplicable for ferromagnetic phase at any anisotropy. We did not find the reorientation phase transition due to dipole-dipole interaction predicted by Pescia and Pokrovsky. Taking into account the spin flips we obtained a phase transition temperature in good agreement with results of our Monte Carlo calculations. These results demonstrate also the effectiveness of the spin wave theory.
ALL-ELECTRON LOCAL-DENSITY DETERMINATION OF THE ELECTRONIC STRUCTURE AND SURFACE ENERGY OF ZR(0001)
Authors: LEE J. I. , HWANG S. K. , HONG S. C. , FREEMAN A. J.
Published: November 2004

The electronic structure and surface energy of Zr(0001) is determined theoretically using the all-electron full-potential linearized augmented plane wave method based on local-density functional theory. We found the value of surface energy to be 1.6 J/m 2 which is comparable to the value estimated from experiments on liquid zirconium at the melting point. It is, however, much smaller than the surface energies of W(001), V(001) and bcc Co(001). The calculated valence charge density, workfunction, and layer projected density of states for Zr(0001) are also presented.
ELECTRONIC STRUCTURE OF THE Mo(001) SURFACE: LOCAL DENSITY STUDY
Authors: HONG SOON C. , LEE JAE IL
Published: November 2004

LEED observed an incommensurate surface reconstruction for the Mo(001) surface and a recent photoemission experiment measured electronic structure of the Mo(001) surface at room and low temperature (52 K). Employing the all-electron local density full potential linearized augmented plane wave (FLAPW) method, we calculated the electronic structure of the Mo(001) surface. Two prominent LDOS peaks at the surface are found just below Fermi level and E b = 0.50 eV and they are confirmed to come from surface states along [Formula: see text] symmetry line. The surface states (just below Fermi level) with even symmetry show no energy dispersion while the surface states ( E b = 0.50 eV ) with odd symmetry have upward energy dispersion from [Formula: see text] to [Formula: see text]. The two bands of surface states fade off at [Formula: see text], which is very consistent with experiments. The work function is calculated to be 4.20 eV. We will present the character of charge densities of the surface states and compare to experiments.
CALCULATION OF SPIN-POLARIZED ARUPS SPECTRA FOR FERROMAGNETIC TRANSITION METAL SURFACES
Authors: AISAKA TSUYOSHI , ISHII AKIRA , YAMADA KUNIKO
Published: November 2004

Calculation of spin-polarized ARUPS spectra for ferromagnetic transition metal surfaces are presented by using non-relativistic multiple-scattering method with time-reversed LEED states. The effects of surface relaxation are investigated and found to be significant for discussing the quantitative discrepancy of the spin-resolved band between theory and experiment at X2 for Ni(110) surface.
ITINERANT ELECTRON MAGNETISM, LOCAL MOMENTS AND THE ONSAGER CAVITY FIELD
Authors: GYORFFY B.L. , STAUNTON J.B.
Published: November 2004

We review the disordered local moment picture of itinerant electron paramagnets. Noting its failure to describe Ni in a first principles calculation we develop the conceptual framework to include an account of the Onsager cavity field in the paramagnetic state. We illustrate the resulting theory by explicit calculations for the Curie temperatures TcFe and TcNi and the susceptibilities χFe(q) andχNi(q).
ITINERANT ELECTRON METAMAGNETISM OF Co-COMPOUNDS
Authors: YAMADA H.
Published: November 2004

On the Landau-Ginzburg theory the metamagnetic transition observed at low temperature in some Co-compounds YCo2, LuCo2, Co(S, Se)2 and others has been shown to be related with the susceptibility maximum at room temperature through a characteristic quantity given in terms of the Landau expansion coefficients of the magnetic free energy. The present theory can explain the metamagnetic behaviours observed in the d-electron system at finite temperature.
FERMION CLUSTER APPROACH TO THE HUBBARD MODEL
Authors: ZIEGLER ALFRED
Published: November 2004

The deficiencies of the fermion cluster approximation by Caron and Pratt out-lined in a previous paper are corrected and the approximation is then applied to the one-site Hubbard model. Because the approximation in its standard form is unable to describe energy bands the boundary condition integration technique of C. Gros for free clusters is generalized to embedded clusters by averaging over the solutions to different self-consistency equations.
MAGNETIC FIELD EFFECT ON SOUND VELOCITY AND ATTENUATION IN AN ITINERANT ELECTRON FERROMAGNET
Authors: KIM D.J. , YOSHIDA Ikuya
Published: November 2004

In this paper we present the result of a systematic numerical calculation on the temperature dependence of magnetic field effects on the velocity and attenuation constant of longitudinal acoustic sound for both TTc of an itinerant electron ferromagnet. Attributing the origin of these magnetic field effects to the change in the screening of the ion-ion interaction which is caused by a magnetic field, first we reformulate this problem in a unified way. Then we make numerical calculation with a simple model electronic density of states and see how sensitively the sign, size, and temperature variation of these magnetic field effects depend on the details of electronic structure and electron interaction. We find that these magnetic field effects can be very strongly exchange enhanced. These findings suggest the possibility of using such magnetic field effects as a probe of the electronic structure and electron interaction in an itinerant electron ferromagnet. Finally we point out that by measuring the magnetic field effect on sound velocity we can infer the effect of the electron-phonon interaction on the magnetic properties.
MAGNETIC PHASES OF BODY CENTERED CUBIC MANGANESE
Authors: SLIWKO V.L. , BLAHA P. , MOHN P. , SCHWARZ K.
Published: November 2004

We have performed Augmented Spherical Wave (ASW) calculations on bcc Mn and confirmed previous results by Moruzzi and Marcus who reported a ferrimagnetic phase. Independent computations employing the full-potential linearized-augmented-plane-wave (LAPW) method led to similar results. Our ASW results yield the total energy and the magnetic moments as a function of volume assuming different (ferro-, ferri-, antiferro-and non-magnetic) bcc related structures with type I, II, and III spin alignments. We relate the relative stability of various phases to band gaps that open at the Fermi energy for certain volumes. The LAPW symmetry-decomposed partial charges allow to analyze the binding mechanism.
IMPURITY EFFECTS ON THE MAGNETIC ORDERING IN CHROMIUM
Authors: FISHMAN R.S. , LIU S.H.
Published: November 2004

It is well-known that impurities profoundly alter the magnetic properties of chromium. While vanadium impurities suppress the Néel temperature TN, manganese impurities enhance TN substantially. As evidenced by neutron scattering experiments, doping with as little as 0.2% vanadium changes the transition from weakly first order to second order. Young and Sokoloff explained that the first-order transition in pure chromium is caused by a charge-density wave which is the second harmonic of the spin-density wave. By examining the subtle balance between the spin-density and charge-density wave terms in the mean-field free energy, we find that the first-order transition is destroyed when the vanadium concentration exceeds about 0.15%, in agreement with experiments.
LOCAL IMPURITY STATES IN ANTIFERROMAGNETIC Cr-ALLOYS
Authors: GALKIN V.YU.
Published: November 2004

The concept of local impurity states within the energy gap of a spin-density-wave (SDW) system is introduced. It is shown that resonant scattering of conduction electrons at these states may lead to greatly enhanced low-temperature resistivity. This impurity resonance scattering (IRS) model is employed to explain the variation of residual resistivity and temperature dependence of resistivity at low temperatures of Cr-Fe and Cr-Si systems on V and Mn doping and application of high pressure.
OBSERVATION OF A SPIN-DENSITY-WAVE COMPONENT IN THE MAGNETISM OF ALPHA MANGANESE
Authors: DE DONCKER G. , ROTS M.
Published: November 2004

An overview of the characterisation of α—Mn obtained by the nuclear perturbed angular correlation technique is presented. We conclude that the two hyperfine fields observed are associated with a coexistence of an local and itinerant magnetism in the matrix.
INVAR BEHAVIOR OF FCC FeNi BULK AND FILMS: A COMPARISON
Authors: WASSERMANN E.F. , DUMPICH G. , KIRSCHBAUM U. , LIANG J.
Published: November 2004

From a comparison of the thermal expansion and magnetization behavior of uhv evaporated fcc FeNi films with the respective bulk we will show that neither the deviation of the moment from the Slater-Pauling curve nor the weak magnetic behavior (small spin wave stiffness) are relevant for the occurence of the Invar effect. Reason is that in the freshly evaporated films the premartensitic transition is prevented, which in the bulk (and 900K annealed films) leads to non propagating longitudinal spin fluctuations, not sensed in inelastic neutron scattering (“hidden excitation”) but contributing in a Bloch like form (T3/2 dependence) to the magnetization.
INFLUENCE OF Bi-ADDITIONS ON THE MAGNETIC AND MICROSTRUCTURAL PROPERTIES OF (Nd, Dy)-Fe-Al-B MAGNETS
Authors: SCHREY P. , VELICESCU M.
Published: November 2004

Powder metallurgical additions of Bi enhance the temperature stability of (Nd, Dy)-Fe-B permanent magnets. Bi is not solved in the hardmagnetic RE2Fe14B phase, thus does not influence the intrinsic magnetic properties, Only the microstructure of the sintered magnets is changed. Addition of a few wt.% of Bi leads to the formation of a new ternary intergranular phase with the composition Nd6Fe13Bi. This phase substitutes partially the intergranular Nd-rich phase providing the magnetic insulation of hardmagnetic grains. An enhancement of HCJ by about 40% was reached at 150 ºC for a Nd15.5Dy1.5Fe74AlB8 magnet containing 2.5 wt.% Bi compared to the Bi-free material.
CALCULATED CRYSTAL FIELD PARAMETERS OF SmCo5 AND RELATED COMPOUNDS
Authors: RICHTER MANUEL , OPPENEER PETER M. , ESCHRIG HELMUT , JOHANSSON BÖRJE
Published: November 2004

The charge distribution of RCo5 is calculated in the local spin density approximation (LSDA), and used to evaluate crystal field (CF) parameters for the 4f states at the rare-earth (R) site. The calculations are based on an optimized LCAO scheme for the conduction electron magnetism and on an 'open 4f core shell' treatment of the localized R 4f moments. The results are compared with the available experimental values and with data from independent density functional calculations. The LSDA calculations are found to yield the correct. sign for all CF parameters, but to overestimate the magnitude of the most essential second order parameter [Formula: see text]. It is shown, that neither a restriction on the lattice terms (as, e.g., in a point. charge calculation) nor an exclusion of these contributions is justified a priori.
FORMATION OF MAGNETIC MOMENTS IN INTERMETALLIC COMPOUNDS AND ALLOYS
Authors: BEUERLE T. , HUMMLER K. , FÄHNLE M.
Published: November 2004

Jaccarino and Walker proposed that in certain alloy systems a considered kind of atom attains a constant value of the magnetic moment if it is surrounded by at least a minimum number of nearest-neighbor atoms of a certain kind, and that it is nonmagnetic otherwise. It is shown by ab initio supercell calculations within the LMTO method that the system Nbi−xMox with 1% iron approximately fulfills the Jaccarino-Walker hypothesis, whereas the alloy FexRh1−x does not. The physical mechanism for the destruction of the Fe moment in bcc alloys with 4d and 5d transition metals is elucidated.
CALCULATION OF RESIDUAL RESISTIVITY FOR FERROMAGNETIC DILUTE NI-ALLOYS
Authors: MERTIG I. , ZELLER R. , DEDERICHS P.H.
Published: November 2004

We report about ab-initio calculations of the residual resistivity and the deviations of Matthiessens rule for ferromagnetic dilute alloys based on Ni (Ni(A) and Ni(A, B), where A and B stand for simple metal or transition metal impurities).

The calculations are based on density -functional theory and the Korringa-Kohn-Rostoker Green's-function method. The transport is described quasiclassically by means of the Boltzmann equation using a two current model for the ferromagnetic host. The scattering properties of one impurity atom are calculated selfconsistently including in addition to the impurity atom one shell of perturbed host atoms around the impurity.
MAGNETIC PROPERTIES OF R2In (R=Gd, Tb, Er)
Authors: RAVOT D. , GOROCHOV O. , ROISNEL T. , ANDRE G. , BOUREE-VIGNERON F. , HODGES J.A.
Published: November 2004

For all the Rare-Earth (R) the R2In form in the same crystal structure (P63/mmc). These compounds show a great variety of magnetic behaviors. When the temperature decreases, the magnetic susceptibility of Er2InTb2In and Gd2In increases, passes through a maximum then decreases. For Gd2In this behavior was associated with change from a paramagnetic to a ferromagnetic then to an antiferromagnetic state. We have performed magnetic, transport (Tb, Er), Mössbauer spectroscopy (Er) and powder neutron diffraction experiments (Gd, Tb, Er) on these compounds. Unlike Gd2In the resistivity of Tb2In and Er2In does not reveal any anomaly at the temperature where the susceptibility begins to decrease and the Tb2In and Er2In magnetizations show the same behavior at all temperatures in the ordered region. Neutron diffraction experiments reveal ferromagnetic and antiferromagnetic structures at low temperature.
LOW-TEMPERATURE SPECIFIC HEAT OF YMn2 IN THE PARAMAGNETIC AND ANTIFERROMAGNETIC PHASES
Authors: FISHER R.A. , BALLOU R. , EMERSON J.P. , LELIEVRE-BERNA E. , PHILLIPS N.E.
Published: November 2004

The low-temperature specific heat of YMn2 has been measured at applied pressures of 0 to 7.7 kbar. A paramagnetic state is stabilized for moderate values of the applied pressure (of the order of 1.6 kbar). A large linear term in the specific heat, which decreases regularly with increasing pressure, is observed in this phase. It is ascribed to giant spin fluctuations associated with a magnetic-non magnetic instability and a strong geometrical spin frustration.
MAGNETIC SUSCEPTIBILITY OF YRh2
Authors: YAMADA H. , STEINER W.
Published: November 2004

Magnetic measurements for YRh2 with the cubic Laves phase structure were performed between 4.2 and 600 K. It was observed that the susceptibility shows a very weak temperature dependence and our data are about 40 % larger than the observed one by Loebich and Raub. On the other hand, the temperature dependence of the susceptibility was also estimated theoretically, by using the density-of-states curve calculated in the tight-binding method and by taking into account the effect of spin fluctuations. A good agreement between our observed and calculated results is obtained.
ANOMALOUS MAGNETIZATION BEHAVIOUR IN U(Ru1-xRhx)Al
Authors: SECHOVSKY V. , HAVELA L. , NAKOTTE H. , DE BOER F.R. , SUGIYAMA K. , ONO M. , KURODA T. , DATE M.
Published: November 2004

URuAl is a paramagnet with a susceptibility maximum around 50 K. The M(B) curve at 4.2 K displays a broad S-shape with a susceptibility maximum around 30 T. These features can be related to magnetic fluctuation effects. Substitution of Ru by Rh leads to a gradual suppression of the M(B) anomalies (and to the onset of ferromagnetism at x≃0.2) which, however, survive even in the ferromagnetic regime. Because of the strong uniaxial magnetic anisotropy, these phenomena are observed only along the c-axis.
MAGNETISM OF Mn ATOMS IN RARE EARTH INTERMETALLIC COMPOUNDS
Authors: SZYTULA A.
Published: November 2004

In this work the magnetic properties (the values of magnetic moments localized on the Mn atoms, the Néel or Curie temperature) of several intermetallic RMn2X2, RMnX2 and RMnX compounds (where R-rare earth atoms, X-Si or Ge) are analysed. The obtained data are correlated with the data for the RMn2 Laves phases. In R—Mn—X intermetallic compounds two critical values of Mn—Mn distances are observed. The first is connected with a transition from a nonmagnetic to a magnetic state, and the second one with the transition from an antiferro- to a ferromagnetic state. The values of the magnetic moment of Mn atoms are analysed. The change in these values in ferro- and antiferromagnetic state is observed. The presented results indicate an itinerant character of magnetic properties of Mn sublattices in these compounds.
MAGNETIC PROPERTIES OF PSEUDO-BINARY Mn1−xFexSn2 ALLOYS
Authors: SHIRAISHI H. , HORI T. , YAMAGUCHI Y. , FUNAHASHI S. , KANEMATSU K.
Published: November 2004

The magnetic susceptibility measurements have been made on antiferromagnetic compounds Mn1–xFexSn2 and the magnetic phase diagram was illustrated. The high temperature magnetic phases I and III, major phases, were analyzed on the basis of molecular field theory and explained the change of magnetic structure I⇌III occured at x≈0.8.
TRANSPORT PROPERTIES OF Mn3−xCoxGaC (x≤0.12)
Authors: KANOMATA T. , HARADA H. , KANEKO T.
Published: November 2004

The electrical resistivity p and the thermoelectric power S of Mn3–xCoxGaC(x≤0.12) are studied to investigate the mechanism of the magnetic order-order transition. The ρ-T curves for samples with 0<x≤0.06 show the appearence of an intermediate magnetic phase. The experimental results suggest that the magnetic phase transitions of Mn3−xCoxGaC should be discussed in terms of itinerant electron magnetism.
TRANSPORT PROPERTIES OF Mn2−xCoxSb (x≤0.30)
Authors: HARADA T. , HASEBE Y. , MORI S. , NISHIMURA K. , KANOMATA T. , KANEKO T.
Published: November 2004

The electrical resistivity ρ and the thermoelectric power S of Mn2−xCoxSb(x≦0.3) are studied. The abrupt change of ρ and S (0<x) appears near the temperature of magnetic order-order transition. S of Mn2–xCoxSb (0≦x≦0.3) is positive in the ferrimagnetic region and negative in the paramagnetic region. we have discussed these behaviour of ρ and S on the basis of the band structure of Mn2sb.
MAGNETO-ELASTIC PROPERTIES OF MnZnSb
Authors: MORI S. , KANOMATA T. , YAMAUCHI H. , YOSHIDA H. , KANEKO T.
Published: November 2004

The temperature dependence of the magnetization ,σ, the pressure effect on the Curie temperature, TC, and the thermal expansion for MnZnSb are measured. The value of dTC/dp is +3.6 K/kbar. Negative exchange strictions are observed for the lattice parameters a and c. The results are discussed using a phenomenological theory based on the molecular field theory.
MÖSSBAUER AND SUSCEPTIBILITY STUDY OF A SPIN-COUPLED HIGH-SPIN FERROUS SYNTHETIC HEME COMPOUND
Authors: SHAEVITZ Ben A. , REED Christopher A.
Published: November 2004

High-field, variable-temperature Mossbauer and magnetic susceptibility data have been recorded for the synthetic five-coordinate ferrous heme [Fe(TPP)(OH)]—as its polycrystalline salt [Na(dibenzo-18-crown-6)(THF)2][Fe(TPP)OH)]—(TPP=tetraphenylporphyrinate, OH= hydroxide). This compound is a model for the P-460 center of hydroxylamine oxidoreductase from Nitrosomonas europae, an ammonia-oxidizing bacterium. An analysis of the data suggests that the extra d-electron of the iron is located in an oblate orbital. The data are also consistent with an intermolecular spin-coupling between pairs of iron atoms. Although a crystal structure is not available for this compound, a structure determination for a closely related compound is consistent with a pairwise iron-iron exchange but does not rule out more complex schemes.
FLUCTUATIONS OF THE EXCHANGE INTERACTION IN AN AMORPHOUS FERROMAGNET Gd68Cu32
Authors: NAKAI IKUO , MAEDA HIRONOBU , AISHII AKIR
Published: November 2004

We have carried out magnetization and extended X-ray absorption fine structure measurements on an amorphous Gd68Cu32 ferromagent to investigate the relation between magnetic properties and the local structure in amorphous materials. Fluctuations in the exchange interaction for the ferromagnet are estimated experimentally within the framework of the nearest neighbor Heisenberg model.
SPIN GLASS DYNAMICS ON A HIERARCHICAL TREE
Authors: ORBACH R. , LEDERMAN M.
Published: November 2004

The configuration space of spin glasses is characterized by the existence of quasidegenerate equilibrium states separated by barriers, ∆(T). A temperature cycling protocol allows extraction of the temperature dependence of a specific barrier. We find ∂∆(T)/∂T depends only on the particular value of ∆(T) and not on the temperature. Using either a power law or an exponential fit (either is equally accurate), integration leads to a divergence of ∆(T) at a particular temperature T* as the temperature decreases, characteristic of the particular barrier considered. This is interpreted as a continuous divergence of barriers as the temperature is lowered, beginning at Tg. Between these divergent barriers, barriers of finite height exist. The time decay of the thermoremanent magnetization at measurement times t much greater than the waiting time tw is a measure of the correlation of the spin glass at time t with the field-cooled state. Using ultrametricity, this enables the extraction of the branching ratio of the “tree” according to which the spin glass states are organized. Experiments are interpreted in terms of a constant branching ratio for the ultrametric tree within the (small) range of overlaps accessible because of the experimental time window.
ON THE NATURE OF NONERGODIC MAGNETIC PHASES IN DISORDERED SYSTEMS BASED ON γ-Ni1–x[Fe(Mn)]x ALLOYS
Authors: MENSHIKOV A.Z. , TEPLYKH A.E.
Published: November 2004

On the results of the magnetization temperature dependences σZFC(T) and σFC(T) the H-T magnetic phase diagrams are drawn for the γ-Fe70Ni30−cMnc alloys in the region of the concentration ferro-antiferromagnetic transition. A model for the temperature phase transformation into a reentrant ferro- and antiferromagnetic spin glass state is offered. It is based on the existence of paramagnetic inclusions in a magnetic matrix with tricritical behaviour above some temperature Tm. When transforming into a spinglass state these inclusions are the sources of a random magnetic field, which at Ti<Tm breaks a topologically infinite cluster into clusters of finite sizes with magnetic moments μj chaotically oriented in space.
MAGNETIC RESONANCE AND MAGNETIZATION IN THE TRIANGULAR ANTIFERROMAGNET CsCuCl3
Authors: PALME W. , KRIEGELSTEIN H. , GOJKOVIC G. , LÜTHI B.
Published: November 2004

Magnetic resonance and magnetization measurements are presented and discussed. It is shown that a previously used triangular three spin sublattice model can explain some experiments. However for the newly discovered high field resonance modes and magnetization experiments parallel to the c - axis a more detailed model with additional interactions is needed.
MAGNETIC AND STRUCTURAL PROPERTIES OF SCANDIUM CHALCOGENIDE SPINELS WITH IRON AND MANGANESE
Authors: PAWLAK LUCJAN , DUCZMAL MAREK
Published: November 2004

FeSc2S4, MnSc2S4 and MnSc2Se4 crystallize in the normal spinel structure. None of them orders magnetically above 4.2 K contrary to FeLu2S4, which orders at 8 K. This difference is discussed as being strongly dependent on the transfer of divalent iron to the octahedral sites and not on the interionic distances.
ITINERANT-ELECTRON ANTIFERROMAGNETISM IN ThMn2
Authors: UHL M. , SANDRATSKII L. , KÜBLER J.
Published: November 2004

The hexagonal Laves-phase compound ThMn2 shows quite unusual magnetic behaviour that originates from itinerant antiferromagnetism in frustrated lattices. Thus, part of the Mn-atoms are nonmagnetic and the remainder forming a triangular magnetic configuration. We report results of local spin-density functional calculations solving the band-structure problem self-consistently by means of the ASW-method. The latter is suitably generalized to deal with non-collinear, spiral magnetic order characterized by an arbitrary wave-vector. Our results explain most of the properties of ThMn2 satisfactorily.
INFRARED SPECTROSCOPY OF H-TERMINATED SILICON SURFACES
Authors: CHABAL Y.J. , HARRIS A.L. , RAGHAVACHARI KRISHNAN , TULLY J.C.
Published: November 2004

In this review, the present level of infrared spectroscopy at surfaces is described by using hydrogen-terminated silicon surfaces as model systems. The electronic structure of the adsorbate, H, and the large mass difference between H and Si simplify the interpretation of the data and make it possible for the theories to give reliable quantitative information. In particular, ab initio cluster calculations provide an accurate structural description and precise vibrational frequencies for various surface configurations, and are used as the basis of a priori simulations of the line shape of H on silicon. A special emphasis is given to the recent discovery of chemical etching to prepare H-terminated silicon surfaces because it has greatly helped in understanding structural and dynamical properties of H-terminated silicon surfaces. In particular, both the energy and phase relaxation of the Si-H stretching vibration on the flat, ideally hydrogen terminated Si(111) surface have been measured directly and evidence for vibrational energy diffusion has been obtained on vicinal, H-terminated Si(111) surfaces. The data and current theoretical understanding of the chemically prepared Si(111) surfaces are presented and discussed.
MAGNETISM OF FREE TRANSITION METAL AND RARE EARTH CLUSTERS
Authors: BUCHER J.P. , BLOOMFIELD L.A.
Published: November 2004

When ferromagnetic (monodomain) transition metal clusters pass through a magnetic field gradient, they deflect towards increasing magnetic field. For transition metal clusters with a size between N=10 and N=400 atoms, the observable effective magnetic moment (similar to magnetization), measured from the cluster deflection, scales with magnetic field, cluster size and inverse of cluster vibrational temperature. The measurements are in quantitative agreement with a picture in which the cluster moments are subject to rapid orientational fluctuations and explore the whole distribution of magnetic moment projections on the field axis on the time scale of the experiment. Intrinsic magnetic moments per atom in excess of the bulk values are obtained.

While transition metal clusters show a size independent behavior of the magnetic properties down to N=20, similar to what was observed previously for transition metal clusters in matrices, rare earth clusters are quite sensitive to symmetry (anisotropy) and exhibit dramatic variations in their magnetic behavior as a function of size. These size-specific variations of the magnetic behavior of clusters have never been seen before. Except for some “magic numbers”, for which the statistical interpretation still holds, an anomalous spreading of the deflection profile is observed. This spreading is due to a strong coupling of the magnetic moment with the cluster body. When the moment is locked to the lattice by strong crystal field anisotropies, the rotational temperature starts to play an important role in the interpretation of experimental data. This distinct behavior points to the fact that 3d and 4f ferromagnets react quite differently to a confined geometry. This dissimilarity is due in part to a different relative importance of magnetic anisotropy energy and exchange energy. It is found that Gd and Tb clusters retain their magnetic order for temperatures well above their bulk Curie temperatures. Three aspects of cluster magnetic properties can be determined by molecular beam experiments:

(i) The effective magnetic moment of a cluster (equivalent to magnetization in a laboratory reference frame),

(ii) the intrinsic quasi ground state properties in the reference frame of the particle, such as the magnetic moment per atom and the temperature dependence of the order parameter, and

(iii) the dynamics of the cluster as a whole. While the vibrational temperature T vib is almost an experimental input, the rotational temperature T rot can be inferred in the case of strong anisotropy.
ELECTROMAGNETIC RESPONSE AND TRANSPORT PROPERTIES OF GENERALIZED FLUX STATES OF THE DOPED MOTT INSULATOR
Authors: KHVESHCHENKO D.V.
Published: November 2004

We consider electromagnetic response and kinetic properties of a strongly correlated two-dimensional electron system having parity- and time-reversal symmetry violating ground state. An important example of such a state is presented by a generalized flux phase of the doped Mott insulator with a fictitious magnetic field commensurate with filling. We observe that electromagnetic response functions of the compressible flux states exhibit no superconducting behaviour. Processes of spinon and holon scattering by fluctuations of a fictitious magnetic field produce a relaxation of the system. On the basis of the quantum kinetic equation we find frequency- and momentum-dependent electrical and thermal conductivities and thermopower of a generalized flux phase.