bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinks in a Quasi‐One‐Dimensional System with a Nearly 1/3‐Filled Band
Authors: Mertsching J. 
Published: July 2007

AbstractThe formation of kinks in a system with commensurability three is studied in a continuum approximation. The width, the amplitude modulation, the spectrum, and the formation energy of the kinks is approximately calculated within the mean‐field approximation. With increasing ratio of bandwidth to gapwidth, the kinks become broader and less amplitude modulated. The number of localized states in the gap increases, and the energy of formation decreases.
Neutron Diffraction and Magneto‐Optical Study of the Effect of Chloride Doping. On the Incommensurate Magnetic Phase of NiBr2
Authors: Day P. , Turner K. , Visser D. , Wood T. E. 
Published: July 2007

AbstractThe magnetic structures of crystals of NiBr2 doped with 2, 5, and 10 mol % NiCl2 are investigated by neutron diffraction and optical spectroscopy, with special reference to the incommensurate helical phase. Behaviour of the magnetic satellite reflections around (003/2) shows that the propagation vector of the helical phase is reduced from 0.15 nm−1 in NiBr2 to 0.12 nm−1 in the crystal doped with 5% NiCl2. The commensurate‐incommensurate transition temperature Tic is similarly reduced, from 22.5 to 17 K. The propagation direction is unaffected by the dopant, remaining along [110]. Although no resolved magnetic satellite reflections are found in the 10% Cl− ‐doped crystal, a difference plot between 7 and 10 K suggests that the incommensurate phase exists below 10 K. The Néel temperatures of the samples show no significant variation with dopant concentration. The intensity of the “cold” exciton‐magnon combination band between 6050 and 6100 Å, which is associated with the incommensurate phase is used to determine Tic and its behaviour in a magnetic field is used to plot magnetic phase diagrams in the Hab‐T plane. No cold band is observed in the 10% Cl− ‐doped crystal. A hot band. resulting from the ferromagnetic component of the intraplanar coupling, is also studied.
Relativistic Theory of Electron and Positron Diffraction at High and Low Energies
Authors: Gevers R. , David M. 
Published: July 2007

AbstractFrom Dirac's equation with a periodical electrostatic potential one finds for both, electrons and positrons, a linear system of first order differential equations for the coefficients in a spinor plane‐wave expansion of the total wavefunction. This system has the same simple structure as the well‐known system of Howie and Whelan, but it is valid without any restriction. It promises to be a good starting point to discuss the several typical diffraction regimes (e.g. the Laue case, the Bragg case, diffraction at very high and very low energies,…) from a general point of view.
Exchange‐Conductivity Broadening of SSWR Line in Metallic Thin Films
Authors: Jirsa M. 
Published: July 2007

AbstractThe exchange‐conductivity contribution to the linewidth of the spin‐wave resonance modes in a metallic film is derived analytically for arbitrary values of the spin‐pinning parameter β in the case of parallel as well as perpendicular static magnetisation, under the assumption of weak interaction between the spin‐ and the electromagnetic solution of the secular equation. Analytical results are compared with those obtained numerically for the full model. Very good agreement between the results of both models and a simple functional dependence of the analytical formulae on β gives a possibility to determine the surface anisotropy constant and other film parameters.
Study of CuK Absorption Edge in Cu(I) Compounds
Authors: Rao B. Jagannatha , Chetal A. R. 
Published: July 2007

AbstractThe shapes of the copper K edge in the compounds CuCl, CuBr, CuI, Cu2O, and chalcopyrite mineral are studied using a Cauchois type X‐ray spectrograph. The electronic transitions 1s → 4s and 1s → 4p are observed in the edges. The transitions are explained on the basis of (Z + 1) analogy. It is also shown that the 4s‐4p orbital separation of an ion in a compound depends on the ionicity of the compound.
The nature of silver impurity atoms in antimony telluride
Authors: Horák J. , Lošťák P. , Šiška L. , Stordeur M. 
Published: July 2007

AbstractUndoped Sb2Te3 and Ag‐doped Sb2Te3 crystals are grown by a modified Bridgman method. Electrical conductivity, Seebeck coefficient, Hall constant, and reflectivity in the region of the plasma resonance frequency are measured. A quantitative analysis of the silver content in the prepared Sb2Te3 crystals is made by atomic absorption spectrometry. For the undoped Sb2Te3 crystals the free carrier concentration and the effective mass in the direction perpendicular to the c‐axis, m⟂, are calculated, using a simplified model. Using m⟂ determined and the value of the plasma resonance frequency the free carrier concentration in the Sb2Te3(Ag) crystals is calculated. According to the results obtained the Ag atoms incorporated into Sb2Te3 crystals have the character of acceptors and the addition of one Ag atom corresponds to the increase in free carrier concentration by two holes. Therefore it is assumed that silver atoms substitute antimony atoms forming thus point defects of Ag″sb with two negative charges. The defects formed by Ag dopants in Sb2Te3 are compared with those in Bi2Se3(Ag) and Bi2Te3(Ag) crystals.
Extended linear chain approximation to the anisotropic ferromagnetic ising model
Authors: Faleiro Ferreira J. R. , Silva N. P. 
Published: July 2007

AbstractApproximate critical temperatures of anisotropic ferromagnetic Ising models are calculated through a recently proposed extended variational method in statistical mechanics. Using a linear chain Ising Hamiltonian in an effective field as trial Hamiltonian, quite good results are obtained.
Crystalline electric field effects in Pr(La, Y) Al3
Authors: Alekseev P. A. , Sadikov I. P. , Shitikov Yu. L. , Markova I. A. , Chistyakov O. D. , Savitskii E. M. , Kjems J. 
Published: July 2007

AbstractThe results of inelastic neutron scattering experiments on Prx(La, Y)1–xAl3 are presented. CEF Hamiltonian is obtained and the concentration dependence of CEF‐parameters is analyzed. Possible reasons of transition widening between the CEF levels in ternary alloys are considered. Experimental evidence of magnetic excitation dispersion is found and the exchange interaction constant is determined.
Lattice dynamics of InP under hydrostatic pressures
Authors: Patel C. , Sherman W. F. , Wilkinson G. R. 
Published: July 2007

AbstractThe lattice dynamics of InP under variable hydrostatic pressures is investigated on the basis of an “eleven‐parameter” rigid‐ion model. The one‐phonon and two‐phonon density of states functions are computed for various pressures and these results are compared with the available second‐order Raman spectra. The mode Grüneisen parameters are calculated at two arbitrary pressures. The effect of high pressure on the phonon dispersion curves is shown to lead to ‘softening’ in the transverse acoustic modes and eventually to a phase transformation of the compound. Interesting effects in the [1, 1, 0] and [1, 1, 1] directions are shown by the transverse acoustic mode gammas with increasing pressure and suggests the domination of short‐range forces in these two directions.
Infrared optical properties of cerium dioxide
Authors: Mochizuki S. 
Published: July 2007

AbstractThe infrared spectra of bulk and thin‐film CeO2 are measured at various conditions by reflection, transmission, and thermal‐emission methods. The reststrahlen reflectivity spectra of bulk CeO2 are analyzed by means of a two‐oscillator dispersion model, and the dielectric properties and the lattice vibrational properties of CeO2 are discussed. The virtual mode (polariton) spectra of the thin‐film CeO2 are analyzed by means of the virtual mode theory of the anharmonic ionic crystal slab.
Point‐ion‐lattice calculations on F+ centers in lithium niobate and lithium tantalate
Authors: Ho Fat Duen 
Published: July 2007

AbstractWave functions for the ground states and the first excited states of the F+ centers in lithium niobate and lithium tantalate are calculated by using the point‐ion‐lattice model exclusive of the effects of polarizations in the first approximation. The Schrödinger equation is solved variationally. The transition energies are obtained by this very simple treatment, which are compared with the available optical data. This calculation yields the results which agree within some 5% and 23% of the experimental values for LiNbO3 and LiTaO3, respectively.
Impurity–host to host–host coupling force constant ratio for 57Fe in rare gas solids
Authors: Paul Prem , Puri S. P. 
Published: July 2007

AbstractLattice dynamical studies of the Mössbauer recoilless fraction and SOD for 57Fe embedded in Ar, Kr, and Xe, are reported by McNab and coworkers, using the rare gas matrix isolation technique. According to them, the f‐values for the various hosts are nearly the same. Making use of the experimentally determined phonon frequency distribution functions for these hosts, an attempt is made to calculate the f‐values in the framework of the Mannheim model. The anharmonicity correction is also applied for temperatures beyond 5 K. It is found that the values of the ratio of the impurity—host to the host—host coupling‐force constants in these lattices change in a way that the f‐values and SOD remain the same, thereby indicating their independence of the host. In accordance with the expectation, no localized modes are found due to the weak binding of the impurity to the host.
A simple model approach to localized‐itinerant magnetism application to rare‐earth intermetallics
Authors: Iannarella L. , Guimarães A. P. , Da Silva X. A. 
Published: July 2007

AbstractThe combined role of intraband and electron‐localized moment exchange in determining the magnetic behaviour of a system composed of itinerant electrons and localized magnetic moments is investigated. Having in mind rare‐earth–transition metal and rare‐earth–normal metal intermetallic compounds, the critical temperature versus de Gennes factors and the temperature dependence of the magnetizations and susceptibilities of the two magnetic species are studied. Results are obtained for two cases, a) a delta‐like band (narrow band limit), and b) a parabolic density of states, using the molecular field approximation both in the treatment of intraband interaction (Stoner‐like description) and electron‐localized spin exchange. Some comments are made on the parallel between computed and measured magnetic quantities in the systems RAl2, RFe2 and R(Fe1–xAlx)2 (0 < x < 1 and R  heavy rare‐earth).
The quantum yield spectra of electron emission of solids in XUV region
Authors: Elango M. , Kikas A. , Nǒmmiste E. , Pruulmann J. , Saar A. 
Published: July 2007

AbstractAn analysis of the physical information containing in the quantum yield spectra of photoelectron emission of solids in the XUV region is presented. It is shown that these spectra may be obtained at least in three meaningful counting regimes: current, pulse, and n‐electron regimes. A proper treatment of the spectra gives quantitative information about secondary electron escape length, escape probability for an electron at surface, and the number of secondary electrons created by one XUV photon. The experiments with alkali chlorides in the 100 to 250 eV photon energy region give the values of 300 to 800 Å for the escape length and 11 to 17 eV for the energy need to create one low‐energy electron.
Experiment investigation on the complex dielectric function of CdS in the exciton and in the plasma limit
Authors: Kreissl A. , Bohnert K. , Lyssenko V. G. , Klingshirn C. 
Published: July 2007

AbstractThe real and imaginary parts of the complex dielectric function of CdS are experimentally investigated for low temperatures and for various excitation conditions. Strong changes of the dielectric function are observed at high excitation in the spectral region below the band edge. Emphasis is put on the variations of the real part at the transition from a low density exciton phase to a high density plasma phase. It is shown, that the Kramers‐Kronig relations are also valid for highly excited semiconductors. The experimental results are compared with recent theoretical predictions.
Theory of auger spectra from disordered alloys the effect of electron correlations in filled narrow bands
Authors: Drchal V. , Kudrnovský J. 
Published: July 2007

AbstractThe theory of the intraatomic core‐valence‐valence Auger spectra from a substitutionally disordered alloy with an initially filled narrow band is formulated within the coherent‐potential approximation in the space of the two‐hole states. The constituent atoms are characterized by their atomic levels Δ and the contact pair interactions U between two electrons (Hubbard model). The exact solution to the problem is found for a particular case with randomness in the pair interactions only. Results of numerical analysis for a simple model based on the scaling‐factor approximation are given to illustrate the basic features of the theory.
Vibrational relaxation in the excited electronic state
Authors: Hizhnyakov V. V. 
Published: July 2007

AbstractA theory of the temporal evolution of the distribution of the configurational coordinate in the excited electronic state of an impurity centre of a crystal, allowing for the process of pulse excitation, is proposed. The lattice vibrations are considered to be harmonic and the quadratic vibronic interaction is taken into account. In this model relaxation is caused by the dephasing of phonons conditioned by their dispersion. Formulas are obtained relating the relaxation characteristics regarded with the dynamical Green's function. The present solution takes exactly into consideration the effect of mixing normal modes at electronic transition and it describes the influence of quantum effects upon the classical turning points of the configurational coordinate. The results of the theory are illustrated with the numerical calculations of the distribution of configurational coordinate and optical spectra.
The structural transition from NaCl to CsCl type in cesium hydride
Authors: Bashkin I. O. , Degtyareva V. F. , Dergachev Yu. M. , Ponyatovskii E. G. 
Published: July 2007

AbstractThe CsH volume is measured in dependence on pressure up to 35 kbar. A structural NaCl to CsCl type transition associated with a volume jump of 8.6% is found at a pressure of about 6.5 kbar. The T—P phase diagram of CsH is plotted in the temperature range 200 to 525 K. The high pressure phase at liquid nitrogen temperature remains metastable down to atmospheric pressure. The lattice parameter of this phase is a = 3.820 Å at 100 K and atmospheric pressure, the lattice parameter of the initial (NaCl type) phase is a = 6.365 Å under the same conditions.
Magnetic and neutron diffraction study of the phase transition in TmFe1−xMnxO3
Authors: Krezhov K. A. , Mikhov M. T. , Kadomtseva A. M. , Krinetskii I. B. , Lukina M. M. 
Published: July 2007

AbstractMagnetic and neutron diffraction investigations on polycrystalline samples of TmFe1−xMnxO3 compounds (x = 0.1 and x = 0.3) reveal some interesting features of the Mn3+‐ion influence on the thulium orthoferrite magnetic properties. Preliminary X‐ray diffraction data indicate an increase of the unit cell distortion with growing content of Mn3+ ions. A decrease of the Néel temperature with higher Mn3+ amount is observed. For the compound with x = 0.1 a reorientation transition from GxFz to GzFx (Γ4 − Γ2) spin configuration is observed, whereas in the case of the compound with x = 0.3 a phase transition to antiferromagnetic phase (Γ1) is established. The neutron diffraction results point out to the occurrence of a complicated transitions sequence in the last case.
A model of titanium luminescence centers in lithium and sodium fluorides
Authors: Radzhabov E. A. 
Published: July 2007

AbstractThe absorption, emission, excitation spectra, and polarized luminescence of titanium centers in lithium and sodium fluorides are studied. The 2.42 and 3.1 eV emissions in LiF:TiO2 and 2.2 and 2.95 eV emissions in NaF:TiO2:MgF2 are related to the electronic transitions of titanium centers. The low energy emissions at relatively low temperatures have the same azimuthal dependence of the polarisation degree as the emission of oscillators oriented along the C2 crystal axis. The high energy emissions are polarized along the C3 crystal axis. The high temperature stability of the polarization degree shows that the luminescence centers have point defects near the titanium ion. The efficiency of transformation of titanium luminescence centers by X‐irradiation grows above 200 K. This points out that the cation vacancies are part of luminescence centers. A model of titanium luminescence centers in lithium and sodium fluorides is suggested. The center consists of a Ti4+ ion at cation site, an O2− ion at anion site, and two associated cation vacancies.
EPR linewidth studies of Gd3+‐doped LaxCe1−xF3 single crystals
Authors: Korczak W. , Paradowski M. , Subotowicz M. 
Published: July 2007

AbstractEPR linewidths of Gd3+ ions (0.1%) in LaxCe1−xF3 single crystals at the frequency 9.4 GHz and temperatures of 77 to 297 K are investigated for H ∥ z. The generalized theory of the magnetic resonance by Kubo and Tomita and Mitsuma's mechanism of spin‐lattice modulated narrowing are adapted to explain the temperature dependence of the EPR linewidths of the Gd3+ ions at the Kramers host Ce3+ ions (4f1, 2F5/2) in LaxCe1−xF3 single crystals for x ⩽ 0.2. The spin‐lattice narrowing is not observed for x > 0.2. EPR linewidth of Gd3+ does not depend on the temperature for x > 0.2. Peak‐to‐peak linewidth ΔHpp increases with the decreasing amount of diamagnetic lanthanum ions in LaxCe1−xF3 single crystals for 0.6 ⩽ x ⩽ 1.
A pair potential calculation of vacancy formation and migration energies for aluminium and copper
Authors: Rautioaho R. H. 
Published: July 2007

AbstractVacancy formation and migration energies and enthalpies are computed for aluminium and copper using potential functions derived earlier by fitting to phonon frequencies. Also, the local density correction proposed by Finnis and Sachdev is evaluated for the formation energy in both the metals. The calculated formation and migration enthalpies, 0.84 and 0.65 eV for Al and 1.38 and 0.80 eV for Cu, respectively, are close to the corresponding experimental values. The results are considered in terms of third‐order contributions of the total energy. The third‐order contribution to the formation energy is expected to be of the order of the experimental formation enthalpy in the case of Al but considerable smaller in the case of Cu. On the other hand, the two‐body potential approach almost suffices to explain the experimental figures for the migration enthalpy, since the third‐order terms for the initial and saddle‐point configurations in the migration process largerly cancel each other.
Theory of the diffusivity—mobility ratio in cadmium arsenide
Authors: Singh M. , Leotin J. , Wallace P. R. 
Published: July 2007

AbstractStimulated by the work of Chakravarti et al. [1], the theory of the Einstein relation for the ratio of diffusivity, D, to mobility, μ, in cadmium arsenide crystals in a magnetic field at low temperatures is developed. D/μ shows characteristic de Haas‐Shubnikov oscillations which vary considerably with orientation of the crystal due to its anisotropy. In fact, for low enough magnetic fields it is shown that it may oscillate as a function of the angle θ between the c‐axis of the crystal and the field direction. Measurements of D/μ would thus constitute a sensitive test of anisotropy. By measuring the variation both, with respect to field and angle for a single sample, all the band parameters can be determined in principle.
Exchange interaction in superconducting metals
Authors: Krüger E. 
Published: July 2007

AbstractFrom the band structures of superconductors it is concluded that the formation of Cooper pairs is connected with exchange interaction existing only in the conduction bands of superconductors. Nevertheless, the pairing is mediated by phonons. This new coupling mechanism, which does not contradict the BCS mechanism, provides an understanding of superconducting properties of materials.
Dynamical susceptibility and electrical resistivity of disordered spin systems
Authors: Goedsche F. , Richter A. , Vojta G. 
Published: July 2007

AbstractA general relation between the electrical resistivity and the dynamical susceptibility of the scattering system, valid in the weak scattering limit and for arbitrary temperatures, is extended to disordered spin systems including elastic spin‐conserving as well as inelastic spin‐flip scattering. Averaging procedures for the position‐dependent susceptibilities are discussed. As an application, the low‐temperature resistivity R is calculated for the Heisenberg‐Mattis model as a site‐random magnet with ferro‐antiferromagnetic exchange disorder. The superposition of the spin‐dependent elastic scattering contributions to R and the contributions due to inelastic scattering by quasipropagating excitations with linear dispersion and quadratic disorder damping yields a weak resistivity minimum. Comparisons with other theoretical papers are made, and the relevance of the results for the interpretation of experimental data is discussed.
Theoretical compton profiles of magnesium
Authors: Rennert P. , Carl G. , Gläser U.‐H. 
Published: July 2007

AbstractStarting from a pseudopotential calculation Compton profiles for h.c.p. magnesium single crystals are calculated. They are given for nine directions and for the directionally averaged case. The complete 〈001〉 profile of Mg is compared with an experimental result. The experimental Compton profile is slightly broader than the theoretical one because of the electron‐electron correlation. The anisotropy for I〈001〉–I 〈100〉 and I 〈001〉–I 〈110〉 is found to be smaller than for experimental profiles but larger than for theoretical ones calculated by the APW method.
A localized orbital description of Si
Authors: Downey M. , Smith P. V. 
Published: July 2007

AbstractIn order to describe the change in electronic structure arising from the presence of impurities in a metal or semiconductor it is convenient to have a localized basis representation of the host. To optimize such impurity calculations it is also necessary that this set of localized basis functions be as small as possible. The best representation of the electronic structure of the diamond and zinc‐blende semiconductors in terms of a small set of localized basis functions has been obtained by Chadi. In this method Bloch sums for describing the pseudo‐wave‐functions and energy bands are constructed from Slater orbitals of different symmetry centred on each atomic site. Using a variational approach to determine the decay constants parametrizing these various orbitals Chadi obtains an accurate description of the bandstructures with a simple four state per atom s–p basis set and reliable pseudo‐charge densities with only ten states per atom. These original calculations of Chadi are not, however, carried through to full convergence. Therefore this analysis is repeated for the case of Si and it is found that, while Chadi's results are indeed fortuitous, it is possible to accurately describe both the bandstructure and valence electron charge density of these semiconductors in terms of a minimum set of well localized basis functions.
Calculation of magnetic hyperfine interactions in the rare‐earth orthoferrites with model covalency parameter
Authors: Flyagin M. Ya. , Men A. N. 
Published: July 2007

AbstractThe magnetic hyperfine fields for some orthoferrites are calculated using the model suggested by Boekema, Van Der Woude, and Sawatzky. The s electrons of the oxygen ion are taken into account also. An approximate formula is proposed to estimate the covalency parameters. The unknown parameters of this formula are determined using the experimental data for LaFeO3. The proposed model describes satisfactorily the observed hyperfine fields for orthoferrites. It is found that the contribution of 2s electrons to the hyperfine field is small.