bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dispersion of Magnon‐Polaritons in Uniaxial Ferrites
Authors: Voss R. , Kotzott R. , Merten L. 
Published: July 2007

AbstractGeneral dispersion equations of magnon‐polaritons in uniaxial ferrites are derived from Maxwell's equations. From these relations the dispersion curves for a simple artificial uniaxial ferrimagnetic crystal are calculated for different angles of wave propagation against the optical axis. The principal differences between the dispersion of ferrimagnetic and antiferromagnetic magnon‐polaritons are pointed out.
Magnetic Excitons in a Spin‐Cluster System
Authors: Meisen A. , Heber G. 
Published: July 2007

AbstractMagnetic properties are calculated in the effective‐field approximation for a four‐level (singlet‐triplet) spin‐cluster system. Furthermore the spectrum of magnetic excitons propagating in this interacting system having in zero order discrete energy levels is studied. For the treatment of the magnetic spin‐cluster crystal the standard‐basis operator (SBO) formalism is applied. The model Hamiltonian used by Heber, Nara, and Freudenhammer is transformed in terms of the SBO's; and the eigen‐values are determined. The thermodynamic properties are obtained from the SBO Green's function equations of motion developing in the random‐phase approximation (RPA). A formula for the magnetization and susceptibility is derived.
Theory for the Magnetic Circular Polarization of the F‐Center Luminescence
Authors: Iwahana K. 
Published: July 2007

AbstractA simple theoretical model is developed for the magnetic circular polarization (MCP) of the F‐center luminescence on the basis of a vibronic theory. In this model new rate equations for the optical pumping cycle are proposed to describe the unthermalized spin systems at low temperatures. It is shown that the model can consistently explain the unusual dependences of the MCP upon the magnetic field and temperature which are observed in the low temperature region. From the analysis of the temperature dependence of the MCP, ΔMCP(T), in the high temperature region, it is found that one must have Δ > 2 as far as V4 ≦ 0.6 to account for the nearly temperature independent behaviour of ΔMCP(T) in KCl in contrast to Δ < 2 given previously from the analysis of the temperature dependence of the radiative lifetime. It is pointed out that the discrepancy may be reconciled if assuming that the contribution to ΔMCP(T) of the field‐induced level splitting in the adjacent excited states is negligibly small.
Trap‐Limited Hopping in One‐Dimensional and Quasi‐One‐Dimensional Systems
Authors: Prigodin V. N. , Seidel Ch. , Nakhmedov A. P. 
Published: July 2007

AbstractTrap‐controled hopping in 1D systems is studied by means of the Berezinsky technique. In the case of a discrete trap niveau exact time and field dependences are given of the relaxation current produced by injected carriers. In an initial time interval any kind of traps acts as deep species and one obtains the same current kinetics as formerly found for the randomly broken bond model, i.e., some exponential dependences. At large times the traps acting as shallow species give rise to a diminished stationary current. The effect of spatial disorder in the hopping sites is discussed. Taking into account a small transverse hopping rate the 1D results are generalized to quasi‐1D systems.
Optical Properties of the Quaternary II–VI Mixed Crystals in the Far Infrared Region
Authors: Burlakov V. M. , Litvinchuk A. P. , Pyrkov V. N. , Tarasov G. G. , Vitrikhovskii N. I. 
Published: July 2007

AbstractThe optical properties of mixed crystals CdTe1−x−ySexSy and ZnTe1−x−;ySexSy are investigated by methods of far infrared spectroscopy. Different types of transformation of the vibrational spectra of these solid solutions with composition are found. The longitudinal and transverse optical vibration frequencies are calculated theoretically by means of a unit cell version of the random element isodisplacement model. The calculations are in satisfactory agreement with the experimental results. The reflection spectra peculiarities with mixed crystal disordering are discussed.
Phonon Dispersion in Platinum and Palladium
Authors: Rajput A. 
Published: July 2007

AbstractA phenomenological model that takes into account both, two‐ and three‐body interactions is developed for the calculation of the phonon frequency spectra of a homogeneously strained facecentred cubic (f.c.c.) crystal. The model is tested by applying it to the calculation of phonon dispersion curves and lattice heat capacity of the transition metals platinum and palladium. The theoretical results are found to agree well with the corresponding experimental data.
Static and Dynamical Valence Charge and Bond Charge Properties of Zincblende Structure Compounds
Authors: Pietsch U. 
Published: July 2007

AbstractBy means of a simple quantummechanical model of the linear superposition of “two‐electron‐molecules” both, the valence charge density and the bond charge density of zinc blende structure compounds are constructed. This scheme makes use of the results calculated for elemental semiconductors. Further it is extended by the self‐consistent determination of the effective charge and by an approximation describing the dehybridization of valence orbitals for increasing ionicity. The estimated valence charge densities are in rather good agreement with those published till now from band structure calculations. The model permits us to explain some known empirical properties concerning the ionicity dependence of the bond charge amount, the effective charge, the value 2e/ε0 defined by the dielectric theory, and the charge dependence of ionic radii. Due to the variation in both, the next neighbour distance and the co‐ordination angles the bond charge amount has to vary for a disturbed lattice. The bond charge transfer constants are calculated for thermal displacement and for hydrostatic pressure.
The Influence of Impurities on the Range of 28 MeV α‐Particles in NaCl Single Crystals
Authors: Basu A. M. , Choudhury A. , Chaudhuri S. , Mukhopadhyay P. , Baliga B. B. 
Published: July 2007

AbstractPure and impurity‐doped NaCl crystals are irradiated with 28 MeV α‐particles at room temperature. The beam current is 2 nA and the irradiation is continued for one minute in each case. Due to irradiation, F‐centers are produced uniformly in the crystals. The beam divergence is estimated from the observed area of the colored circular spot on the crystal. The optical absorption band of the colored samples are recorded. The efficiency of coloration (F‐center) is determined and is found to be independent of orientation and concentration of impurities in the crystal. The range of α‐particles is measured, which is found to be shorter in impurity‐doped crystals than in pure crystals. The results are explained in terms of recent observations.
Specific Heat and Magnetocaloric Effects in TbPO4. II. Mean Field Theory
Authors: Kasten A. , Üffinger G. 
Published: July 2007

AbstractThe magnetic phases and crystal distortions occurring in TbPO4 at low temperatures are described in mean field theory taking into account the influence of exchange and dipole interaction, Jahn‐Teller coupling, and the external field. The calculations are compared with the results of specific heat and magneto‐caloric measurements. The theory reflects the qualitative behaviour but there are still considerable differences. In an extended model, a magnetisation‐dependent exchange interaction is introduced leading to a better agreement in low fields.
The Classical and Generalized Moment Problem in the Theory of Relaxation
Authors: Giannozzi P. , Grosso G. , Parravicini G. Pastori 
Published: July 2007

AbstractThe classical moment problem for continued fraction expansion of relaxation functions is surveyed. The theory is then extended to the moment problem associated to relaxation operators or super‐operators. Numerical aspects and sensitivity of algorithms to round‐off errors are also examined. A new convenient approach is developed exploiting a product‐difference recursive scheme, within the memory function formalism.
Spectroscopic Investigation and Polarized Luminescence of Silver Pair Centers in Sodium Chloride
Authors: Atoussi B. , Pedrini C. , Moine B. , Madej C. 
Published: July 2007

AbstractAbsorption, emission, and excitation spectra of heavily Ag+ doped NaCl single crystals are investigated at various temperatures. Besides the ultra‐violet emission due to Ag+ single ions and the violet emission already observed, the crystal displays a new green fluorescence. It is shown that the fundamental emitters in the visible range are (Ag+)2 pair centers. The polarization properties of luminescence of dimers are carefully analyzed. The measurement of the magnitude of the degree of polarization of fluorescence and its azimuthal dependence suggest that the two (Ag+)2 luminescent centers are oriented along the C4 axes of the crystal. Models for the paired (Ag+)2 centers are proposed and some of their spectral properties discussed.
Annihilation of Frenkel Pairs in B.C.C. Metals (α‐Iron). II. The Case of the Unstressed Lattice (Numerical Results)
Authors: Ratishvili I. G. 
Published: July 2007

AbstractA model describing the Frenkel pair annihilation process is presented. The annihilation rate is assumed to be governed by two factors: the distribution function X(r), giving the initial relative spacing of the components of a Frenkel pair, and the distribution function F(r), describing the potential barriers in the vicinity of a vacancy‐interstitial pair. Numerical calculations are performed for the case of the b.c.c. lattice of α‐iron and the results are compared with the experimental data. In the proposed scheme of description the existence of a number of substages at the first annealing stage is explained easily.
Chemical Activity of Noble Gases in Diamond
Authors: Tkachev V. D. , Zaitsev A. M. , Tkachev V. V. 
Published: July 2007

AbstractThe matrix distortion influence on the noble gas atoms He and Ne introduced into diamond by ion implantation is discovered and explained. Consequences of the effect mentioned are the chemical activity of the noble gas atoms in diamond lattice and the formation of stable impurity‐defect complexes, as it follows from the investigation of Mössbauer‐type luminescence spectra.
Indirect Magnetoelastic Interaction and Magnetostriction of Dilute Rare‐Earth Alloys
Authors: Kozarzewski B. , Kurzyk J. , Deniszczyk J. 
Published: July 2007

AbstractThe theory of indirect magnetoelastic interaction in dilute rare‐earth alloys is rederived in more general form. Expressions are obtained for conduction electron contribution to the crystal field parameters and magnetoelastic coupling constants. They appear to depend on Slater integrals, electron‐phonon interaction, and band structure of the alloy. The particular case of an alloy of the cubic symmetry is discussed as an example. Magnetoelastic coupling constants of some AgRE alloys are calculated within the nearly free electron approximation for the Ag band states.
A Discussion about the N‐Pole Approximation to the Continued‐Fraction Expansion
Authors: Pires A. S. T. 
Published: July 2007

AbstractThe conditions are studied to be satisfied in order to use a N‐pole truncation to the continued‐fraction expansion. The correct way is shown to do the cut off and the result are applied to analyse experimental data for the unidimensional antiferromagnetic TMMC at low temperatures.
Light Scattering by Surface Ripples in a Spatially Dispersive Medium
Authors: Albuquerque E. L. , Almeida N. S. , Oliveros M. C. 
Published: July 2007

AbstractA theory is presented of the scattering of light by acoustic surface‐ripple in a medium which shows spatial dispersion for any polarization of the incident light. The exciton‐photon interaction, leading to the exciton‐polariton, is described in a purely phenomenological way, as in the early description of the phonon‐polariton. Some numerical results of the scattering cross section due to surface waves of the Rayleigh type are also presented and their features discussed.
Integration over the Two‐Dimensional Brillouin Zone
Authors: Kurganskii S. I. , Dubrovskii O. I. , Domashevskaya E. P. 
Published: July 2007

AbstractA new method is proposed for the calculation of integrals over the two‐dimensional Brillouin zone (BZ) such as the density of states. The BZ is subdivided into triangles, in which quadratic interpolation over six points for the integrands in wave vector is used, and further subdivision of the BZ into smaller triangles appears to be possible. In each of the “small” triangles obtained the integrals are taken in analytical form on the supposition of linear dependence of integrands on wave vector. Tests of the calculation of the free electron density of states shows quite a high efficiency of the hybrid triangle method.
Calculation of the Thermoelectric Power of Ga, Ni, Rh, and Pd Impurities in Copper
Authors: Mertig I. , Mrosan E. , Zeller R. , Dederichs P. H. , Ziesche P. 
Published: July 2007

AbstractStarting from the Mott formula the thermoelectric power for Ga, Ni, Rh, and Pd impurities in a copper host is calculated taking into account the full anisotropic electronic band structure of the host. The necessary Fermi surface integrations are performed numerically using the tetrahedron method. The calculation of the scattering properties of the impurities is based on density functional theory in the local density approximation and on the KKR Green function method. The muffin tin potentials of the impurity are calculated self consistently. Theoretical results for the thermoelectric power and also for the residual resistivity are discussed in relation to recently measured values.
Charge Carrier Mobility Caused by Scattering from Hybrid Plasmon–Phonon Modes
Authors: Kasiyan A. I. , Russu P. I. 
Published: July 2007

AbstractA polar semiconductor containing one‐component electron plasma of free charge carriers is studied. The carrier density is assumed to vary over a wide range from a non‐degenerate state to a high degenerate plasma state. The interaction between the L O phonons and charge carrier plasma modes leads to hybrid plasmon‐phonon branches in the spectrum. The spectrum of renormalized plasmon‐phonon modes is calculated for PbTe and GaAs crystals. The electron mobility as a function of carrier density is investigated considering electron scattering by renormalized plasmon‐phonon modes both, in non‐degenerate and degenerate specimens of these crystals.
A Pseudopotential Approach to the Structural and Thermodynamical Properties of III–V Ternary Semiconductor Alloys
Authors: Ito T. 
Published: July 2007

AbstractThe structural and thermodynamical properties of III–V ternary semiconductor alloys (AlGaAs, AlGaSb, AlInAs, AlInSb, GaInAs, and GaInSb) are investigated using a pseudopotential perturbation treatment. A simple calculation method is proposed to estimate the disorder contribution to the total crystal energy of III–V ternary semiconductor alloys. The calculated results of compositional lattice parameter are in good agreement with the previously reported experimental data. Phase diagram calculations of III–V pseudobinary systems are also successfully achieved.
Mössbauer Diffraction in the Superionic Conductor RbAg4I5
Authors: Zolotoyabko E. V. , Ovanesyan N. S. 
Published: July 2007

AbstractThe problem of Mössbauer diffraction on crystals with intensive diffusion is analysed for the case of the superionic conductor RbAg4I5. An expression for the Mössbauer spectra of the diffracted beam is given for different diffusional model. The experimental temperature dependence of the coherent scattering of Mössbauer radiation in this sample is interpreted on the basis of developed theoretical assumptions.
Optical Anisotropy and Dichroism of A‐Centres in NaCl and KCl Single Crystals Irradiated with X‐Rays under DC Fields
Authors: Chaudhary R. K. , Rao A. V. Krishna , Rao K. V. 
Published: July 2007

AbstractThe optical absorption characteristics of the Petroff A‐band reported in our earlier work on NaCl and KCl single crystals X‐ray irradiated under dc fields, are studied in greater detail using polarized light. The results seem to indicate that the A‐centres exhibit anisotropic and dichroic behaviour. A possible explanation of the results is attempted.
Active Representations in Crystals of Cubic Symmetry
Authors: Hatch D. M. , Stokes H. T. 
Published: July 2007

AbstractThe reality, Landau, and Lifshitz conditions are reviewed within the formalism of the Landau theory of continuous phase transitions in crystals. It is shown that an incorrect use of these conditions in the literature has led to an omission of the W‐ and P‐point representations in the Oh crystal class. A detailed example for the W‐point is considered and the correct results obtained. The correct listing is given of the reality, Landau, and Lifshitz conditions for the entire cubic system (i.e., the classes T, Th, O, Td, and Oh).
Molecular Dynamics Study of Thermodynamics and Structure of Liquid Sodium under Pressure
Authors: Polukhin V. A. , Bratkovskii A. M. , Vaks V. G. 
Published: July 2007

AbstractBy the molecular dynamics method using 864 atoms the structural and thermodynamic properties of liquid Na are calculated for two states on the melting curve, which correspond to compressions u = 0 and u ≈︁ 20%. The radial distribution function g(r), structure factor S(k), energy U, and pressure p are found. Both, g(r) and S(k) are similar in the two states and differ mainly in a simple compression of all the scales. This similarity is in agreement with the hypothesis of the existence of the “crystallization criterion”, the universality of the short‐range order on the melting curves for simple liquids. A comparison with the Pereus‐Yevick (PY) approximation for S(k) shows that at u = 0 SPY(k) is close to SMD(k) and to the experiment, while at u ≈︁ 0.2 SPY(k) and SMD(k) diverge sharply, which is, apparently, due to the decreasing of the accuracy of the PY approximation at considerable values of u.
Random‐Field Correlations and Quantum Critical Phenomena
Authors: Uzunov D. I. , Korutcheva E. R. , Millev Y. T. 
Published: July 2007

AbstractThe effect of quenched random fields on the zero‐temperature critical behaviour is studied by the means of the Wilson‐Fisher renormalisation‐group recursion relations to first order in the ϵ‐expansion. A number of quantum models is considered. The simultaneous influence of both, the random‐field and the classical‐to‐quantum dimensional crossover phenomena on the quantum critical behaviour is investigated. A special attention is paid to the properties of some reasonable particular forms of Gaussian random correlations which might be of relevance to the description of natural systems.
XPS Study on a‐GeOx (1.3 < x < 2) Films Prepared from GeO2
Authors: Takano Y. , Tandoh Y. , Ozaki H. , Mori N. 
Published: July 2007

AbstractAn XPS study is made on a‐GeOx films prepared by deoxidizing GeO2 in Ar—H plasma. The XPS spectra of Ge 3d electrons are decomposed to five components, whose chemical shifts are estimated by taking into account the remote inductive effect and using the modified Sanderson method. The results are well explained by the model for the atomic configuration in the region of 1.3 < < x < 2.
Resonant Raman Scattering in Ga1—xInxP Solid Solutions
Authors: Bedel E. , Carles R. , Zwick A. , Renucci M. A. , Renucci J. B. 
Published: July 2007

AbstractResonant Raman scattering is investigated around the fundamental edge E0 in Ga1—xInxP solid solutions. The strong enhancements of the “forbidden” LO‐like modes are explained by a Fröhlich intraband interaction and lead to replica of the first‐order spectra. The non‐homogeneous activation of the one‐phonon density of states and the unusual sharp enhancements of LA‐like modes are interpreted as due to structural disorder effects. Local chalcopyrite arrangements are suggested.
Laser Induced Defects in GaAs Layers
Authors: Wesch W. , Wendler E. , Götz G. , Unger K. , Röppischer H. , Resagk Chr. 
Published: July 2007

AbstractAnnealing of ion implanted GaAs layers as well as irradiation of unimplanted samples with nanosecond laser pulses is connected with the formation of exponential absorption tails near the fundamental absorption edge with the dependenceK˜ exp [ħω(E)−1] on the photon energy. Identical behaviour is found in weakly damaged ion implanted layers. The observed high near edge absorption is connected with almost no refractive index change. The characteristic energyEis independent on the implanted ion species and increases with the nuclear deposited energy density and the laser energy density from about ≈ 0.1 eV up to a maximum value of 0.52 eV. The defects responsible for this behaviour act as compensating centers for free carriers. The experimental findings and the missing pronounced absorption tail in irradiated silicon supports the conclusion that defects typical for compound semiconductors are produced. Assuming high concentrations of vacancies and anti‐site defects the experimentally found values forEcan be explained from theoretical calculations.
The Effect of a Cu Overlayer on the Magnetization of an Fe Film
Authors: Schröder K. 
Published: July 2007

AbstractThe effect of a Cu overlayer on the magnetization of an Fe film is measured at room temperature in a high‐vacuum system. The deposition of Cu leads to an increase of the magnetic moment. If one associates this with the magnetic moment in the top monolayer of the copper film, then the measurements suggest that the magnetic moment of the copper film surface is equivalent to the magnetic moment of an iron film 0.16 nm thick.
Photoionization Cross‐Section for δ‐Shell Deep Levels
Authors: Masut R. , Penchina C. M. 
Published: July 2007

AbstractA δ‐shell model is presented of deep impurities in semiconductors as a simple but effective extension of the well‐known δ‐function model of Lucovsky, in order to address the problem of fairly sharp photo‐ionization spectra. Whereas Lucovsky treated only the photo‐ionization of electrons from s‐like impurity states to the conduction band (forbidden transitions), this paper considers also the photo‐ionization of holes to the valence band (allowed transitions). The new δ‐shell model gives an improved fit to experimental photo‐ionization data. It can be used to determine the range of the deep impurity potential as well as the binding energy, and can help to determine the nature of the photoionized charge (electron/hole).
Theory of Luminescence Anisotropy of YAlO3:Nd3+ Single Crystals
Authors: Aminov L. K. , Kaminskii A. A. , Chertanov M. I. 
Published: July 2007

AbstractBased on the microscopic model of activator centres in crystals theoretical calculations of the anisotropic intensity of luminescent radiation of Nd3+ ions in the YAlO3 single crystals are carried out. The parameters of the effective electric‐dipole moment operator of Nd3+ ions describing the probabilities of the transitions in 4F3/2 → 4I9/2‐15/2 channels are obtained and the interference of two basic electric‐dipole transition mechanisms are taken into account. In one of these mechanisms electric‐dipole transitions are allowed due to the mixing of opposite parity states to the ground 4fN‐configuration of the lanthanide ions by the odd terms of the crystal field, in the another one the f‐f transitions are induced by variable components of the even crystal field modulated by the radiation field. The obtained anisotropy of the luminescent inter‐manifold branching ratios and calculated lifetime of the 4F3/2 state of Nd3+ ions well agree with experimental situation. Using as an example the results obtained in this work, the question of the applicability of the present model for the analysis of the spectral properties of anisotropic crystals doped with Ln3+ ions, is discussed.