bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory of electron spin resonance in graded mixed semiconductors
Authors: Leibler L. 
Published: July 2007

AbstractIn semiconductor alloys with non‐uniform composition the spin—orbit coupling leads to specific spin‐dependent effects in free‐carrier dynamics. As a result, conduction electron states in the uniform magnetic field substantially differ from those in homogeneous alloys. It is shown that the electron spin resonance (ESR) is strongly affected by the composition gradient. The polarization dependence of ESR absorption permits to separate easily the effect of crystal non‐homogeneity. The measurement of ESR in graded mixed semiconductors may furnish parameters crucial for determination of the band structure of semiconductor alloys.
On the nature of the top of the valence band in layered Mo and W dichalcogenides
Authors: Fonville R. M. M. , Geertsma W. , Haas C. 
Published: July 2007

AbstractThe magnetic susceptibilities of single crystals of MoS2, MoSe2, α‐MoTe2, and WSe2 are measured between 2 and 300 K. Above 60 K the susceptibilities are temperature independent and strongly anisotropic. The observed anisotropy is attributed to Van Vleck temperature‐independent paramagnetism of the d electrons. The electrical resistivity and the Hall effect of As‐doped p‐type single crystals of MoS2, MoSe2, α‐MoTe2, WS2, and WSe2 are measured between 2 and 300 K. Electron paramagnetic reasonance of p‐type crystals of MoS2, MoSe2, α‐MoTe2, WS2, and WSe2 shows strongly anisotropic g‐values. An explanation of these g‐values is not possible in terms of only metal d‐orbitals or only chalcogen p‐orbitals, but requires a strong mixing of d‐ and porbitals in the top of the valence band.
Effects of bond dilution on dynamics of anisotropic paramagnets at high temperatures
Authors: Kawasaki K. , Tahir‐Kheli R. A. 
Published: July 2007

AbstractWave‐vector dependent frequency moments, for longitudinal and transverse spin correlations, in a cylindrically symmetric, anisotopic paramagnet at T = ∞ with exchange bond dilution are evaluated. Using the phenomenological, two parameter Gaussian construct for the diffusivity, the correlation functions are computed. Two types of dilution are considered: first, when the existence of transverse and longitudinal exchange bonds depends only on a single random variable, and secondly, when these bonds are functions of two independent random variables. It is found that the independent fluctuation of transverse and longitudinal exchange bonds has far reaching consequences. In particular, for a given concentration of connected bonds, the effects of dilution are considerably enhanced when these bonds are fluctuating independently. The relevance of such a model to amorphous paramagnets is noted.
Theory of the X‐ray and optical properties of polysulphur nitride
Authors: Friesen W. I. , Litvin D. B. , Bergersen B. 
Published: July 2007

AbstractThe extended Hückel method is used to calculate various band structure dependent properties of polysulphur nitride (SN)x. X‐ray emission spectra are computed and are presented as a means of differentiating between conflicting reported band structures. The interband contribution to the imaginary part of the dielectric function is also calculated and is discussed in relation to experimental results quoted in the literature.
Thermal expansion and Grüneisen parameters in alkali metals
Authors: Vaks V. G. , Zarochentsev E. V. , Kravchuk S. P. , Safronov V. P. , Trefilov A. V. , Kravchuk S. P. 
Published: July 2007

AbstractThermal expansion and Grüneisen microscopic and macroscopic parameters γvk and γ(T) in the alkali metals are calculated in the pseudopotential model described earlier. γvk is proved to be sensitive to the form of the dielectric function ε(q) and of the pseupotential V(q) so that measurements of γvk may give an information on the ε(q) and V(q). γ(T) has a pronounced variation at small T. Comparison with experiment reveals a high accuracy of the description of the thermal expansion in Na and Cs with the models from [1] and in K and Rb with the models from [2]. Results for Li disagree noticeably with experiment. The sensitivity of all the results to the form of ε(q) and V(q) is discussed.
Phonon scattering on small‐radius colloids in KCl crystals
Authors: Altukhov V. I. , Kvachadze V. G. 
Published: July 2007

AbstractThe heat conduction of KCl is considered taking into account phonon scattering on colloids of different sizes, Estimations for average sizes and concentrations of colloids in KCl are obtained. Peculiarities of formation of small colloids (10 to 30 Å) are discussed. It is shown that with the increase of low‐temperature reactor irradiation dose (or degree of doping) of crystals four characteristic stages of defect formation can be differentiated: (a) point defects, (b) large size colloids and point defects, (c) small colloids (partially due to the decrease of number of large colloids), (d) small and large colloids which are formed in succession. Annealing (in case of doping) leads to a significant enlargement of colloids (partially due to the decrease in number of point defects).
The electronic band structure and interatomic bond in nickel and titanium hydrides
Authors: Kulikov N. I. , Borzunov V. N. , Zvonkov A. D. 
Published: July 2007

AbstractUsing an approximation for solving the Korringa‐Kohn‐Rostoker equation the band structure of titanium and nickel dihydrides and nickel hydride are calculated. The results are compared with experimental data. The applicability of the anionic and protonic models of hydrides are discussed. From the tendency of the palladium hydride band structure one can conclude that nickel dihydride has a superconducting transition at nonzero temperature. The results of band structure calculations of titanium dihydride allow to explain the f.c.c.‐f.c.t. phase transition for this compound.
On the influence of background radiation on Landau emission spectra
Authors: Müller W. , Overhamm M. , Bauer G. , Gornik E. , Grosse P. , Pötzl H. W. , Rautenberg M. 
Published: July 2007

AbstractLandau emission in n‐InSb has been investigated by photoconductive techniques and Fourier transform spectroscopy (FTS). It is found that effects of 300 K background radiation can strongly influence the observed spectra through the electric field induced variation of the optical constants. Only under 4.2 K background conditions or by using special experimental arrangements the influence of the background radiation can be avoided and pure emission spectra are obtained. Real emission spectra consist of two main lines due to Landau level transitions with different spin orientation and a weak impurity line. No emission is observed above the reststrahlen band.
Local Heine‐abarenkov model potential for covalent crystals
Authors: Soma T. 
Published: July 2007

AbstractA local Heine‐Abarenkov model potential is proposed for diamond type crystals. Two parameters are determined by satisfying the zero pressure condition and the first zero of the empirical pseudopotential interpolated from band calculations. Calculated values of bulk modulus for Si, Ge, and α‐Sn are in good agreement with the experimental data.
Some observable consequences of kinetic many‐body treatment of large energy fluctuations and of rate constants in solids
Authors: Khait Y. L. 
Published: July 2007

AbstractSemiphenomenological classical non‐equilibrium collective treatment of short‐lived large energy fluctuations (SLEFs) of heavy particles (atoms, etc.) in bulk and on surfaces of solids up to ε ≧ E ≫ kT are considered. The SLEF probability and rate constants are calculated. In the Arrhenius approximation the calculated pre‐exponential factors are exponential functions of E, effective coordination numbers χeff, Debye temperatures θ, etc. The new interpretation of diffusion and desorption experimental data narrowing the discrepancies between the latter and theoretical predictions is suggested.
Non‐linear fluorescence quenching in molecular crystals I. Recombination of localized excitons
Authors: Benderskii V. A. , Kh. Brikenshtein V. , Lavrushko A. G. , Filippov P. G. 
Published: July 2007

AbstractFrom the measurements of quantum yield and fluorescence decay time of anthracene and naphthalene crystals for different pumping levels at 300 K the rate constants of bimolecular recombination of excitons are found to γ = (1 ± 0.3) × 10−8 and (3 ± 1.5) × 10−11 cm3 S−1, respectively. The relationship between the recombination constants and the interaction radius R0 is calculated for the dipole‐dipole mechanism of recombination. Based on this assumption the values of R0, (40 ± 5) Å in anthracene and (25 ± 5) Å in naphthalene, agree with the values calculated from the overlap of fluorescence and lower excited singlet state absorption spectra.
Exchange splitting of ionic S‐State in MnFe2O4 studied by neutron spectroscopy
Authors: Ligenza S. 
Published: July 2007

AbstractInelastic neutron scattering is used to investigate spin interactions in polycrystalline MnFe2O4. Neutron spectra connected with local spin interaction (not perturbated by cooperative phenomena) are observed and interpreted basing on the 6S5/2‐term splitting of ions situated in octahedral B‐sites and tetrahedral A‐sites. In the analysis of 6S5/2‐term splitting the phenomenological spin‐Hamiltonian is used, assuming a magneto‐electric interaction of spins. The transition energy peaks connected with different magnetic coordinations at B‐sites and A‐sites are observed. Defining the interaction between pairs of spins as — 2JABSA · SB it is found that JAB/k = (– 20.0 ± 0.7) K, in agreement with the result obtained from magnon dispersion measurements.
Electromigration in liquid metal alloys
Authors: Sorbello R. S. 
Published: July 2007

AbstractStarting from an earlier pseudopotential result of Sorbello an expression is obtained for the driving force for electromigration in liquid metal alloys. The resulting force expression is equivalent to the Faber formula. This formula is extended to include electron‐ion potentials which are described by t‐matrices in a phase‐shift representation. Calculations are made for Na–K and Na–Rb alloys using a modified substitutional model for partial ionic structure factors and using the phase shifts computed by Meyer, Nestor, and Young. The theoretical calculations predict reversals in the direction of alloy separation near the experimentally observed values.
Phonon scattering and effect of dislocations on the low‐temperature phonon conductivity in Ge
Authors: Singh M. 
Published: July 2007

AbstractIt is shown that the theory, which is based on the scattering of phonons by bound dangling electrons associated with the dislocation core, gives excellent agreement between the theoretical and experimental results of phonon conductivity for deformed germanium. No adjustable physical parameter is used in the calculation except the difference of energy splitting. From a comparison of theory and experiment is found that the density of dangling electrons is directly proportional to the dislocation density.
Organic metals: Chain stabilisation in bipyridinium‐TCNQ salts
Authors: Ashwell G. J. 
Published: July 2007

AbstractA method of conductivity enhancement applied to bipyridinium‐TCNQ salts is reported. By altering the cation geometry, with careful consideration to the effect on the stacking characteristics of the counter ion, chain stabilisation and conductivity enhancement are achieved. The crystal structures and properties of several bipyridinium‐TCNQ salts are reported. Their conductivities are in the range 10−5 to 103 Ω−1 cm−1 at 300 K. The effect of clathrated solvent molecules on the properties is also discussed.
Quadrupolar–Paramagnetic Critical Temperature of a Spin‐One Isotropic Heisenberg Film with Biquadratic Interactions
Authors: Corciovei A. , Mazilu D. , Mihalache D. 
Published: July 2007

AbstractUsing the Green function method, the transition temperature from the quadrupolar to the paramagnetic phase of an isotropic Heisenberg film with free surfaces in the presence of biquadratic exchange is obtained as the unique solution of a non‐linear system of equations. The other unknowns entering the system are related to the distribution of the quadrupolar order parameters at the critical temperature. The index λ of the relative shift of the critical temperature satisfies the relation λ = 1/ν = 2, ν being the bulk correlation length exponent.
On Integeral Characteristics of the Electron Structure of Crystalline Surfaces
Authors: Bartoš I. , Hietschold M. , Paasch G. 
Published: July 2007

AbstractFormulas giving new applications of the surface Green function formalism to the integral characteristics of surfaces — deviations of the total density and integrated density of electron states, surface energy — are given and applied to a step potential two‐band model of a crystal surface. The role of surface electron states on the behaviour of integrated characteristics is described. The formalism is applicable to any interface problem.
Electron Paramagnetic Resonance of Divalent V, Mn, and Co in Single Crystals of CdI2 and PbI2
Authors: van der Valk H. J. L. , Meertens P. , Haas C. 
Published: July 2007

AbstractEPR spectra are reported of V2+, Mn2+, and Co2+ in CdI2 and PbI2 single crystals. The g‐values of V2+ are strongly affected by covalent mixing of metal 3d with iodine 5p orbitals. The ligand hyperfine interaction is different for Mn substituted in CdI2 and PbI2, respectively. The change is attributed to a different covalent bonding in the two lattices due to the local distortion of the MnI6 octahedra. The temperature dependence of the zero‐field splitting of Mn2+ is explained in terms of the anisotropy of the nuclear vibrations.
Negative Magnetoresistance in Indium Arsenide in the Extreme Quantum Limit
Authors: Mansfield R. , Azhdarov G. 
Published: July 2007

AbstractThe results of magnetoresistance measurements of n‐InAs with carrier concentration ≈ 1016 cm−3 are given in a longitudinal magnetic field up to 40 kG and the temperature range from 20 to 110 K. In a large magnetic field a negative magnetoresistance is observed over the whole investigated temperature range. Under the extreme quantum limit conditions and when impurity scattering predominates, a comparison between the experiment and Argyres and Adams' theory with allowance of Dubinskaya for forward scattering is made and is discussed.
Model Calculations for the Anisotropy Formation by Resputtering Processes during the Growth of Amorphous GdCo Films
Authors: Müller H.‐R. , Perthel R. 
Published: July 2007

AbstractIn order to understand the formation of a magnetic anisotropy during the preparation of amorphous GdCo films by bias sputtering, model calculations are carried out for simple cubic or hexagonal close packed lattices. A structural anisotropy is always obtained, if differences in the binding energies of CoCo, GdCo, and GdGd pairs are assumed. The anisotropy can be described as a difference of the pair numbers parallel and perpendicular to the film plane. Sign and magnitude of the anisotropy depend strongly on the surface configurations involved in the resputtering process (adatoms or inner atoms) and on the binding energies assumed for the different pairs.
Phase Transformations in Hydrides of Rare‐Earth Metals under Pressure. II. The Sc‐H and Yb‐H Systems under High Hydrogen Pressure
Authors: Bashkin I. O. , Ponyatovskii E. G. , Kost M. E. 
Published: July 2007

AbstractThe ScH and YbH systems are investigated at hydrogen pressures up to 13 kbar. A new scandium hydride of the composition ScH2.80 and an ytterbium hydride of the composition YbH2.72 is obtained. The hydrides obtained liberate hydrogen at atmospheric pressure to compositions YbH2.70 and ScH≈2.65. According to the results of X‐ray studies, YbH2.70 remains cubic (a0 = 5.178 Å), while the metastable ScH2.65 consists of the following two phases: f.c.c. (a0 = 4.784 Å) and h.c.p. (a0 = 3.380 Å; c0 = 6.135 Å; c/a = 1.815).
Higher Anharmonicities in the Improved Unsymmetrized Self‐Consistent Field Approximation for a Crystal. I. General Consideration
Authors: Zubov V. I. 
Published: July 2007

AbstractStrongly anharmonic crystals are described by the unsymmetrized self‐consistent field method. When the lowest‐orders anharmonicities are taken into account, the basic nonlinear integral equation is reduced to a set of transcendental equations which can be solved numerically. Such an approach is used as a zeroth‐order approximation. The statistical perturbation theory enables one to take into account the effect of higher‐order anharmonicities on the Helmholtz free energy and on the thermodynamic properties of strongly anharmonic crystals. First‐ and second‐order perturbation theory is considered. The various contributions to the properties of solid Ar are calculated versus temperature and volume.
Localized Bipolarons in Ionic Crystals
Authors: Vinetskii V. L. , Kudykina T. A. 
Published: July 2007

AbstractThe localized bipolaron state in ionic crystals is investigated taking account of the exchange interaction. The state is shown to be thermally stable under all values of the parameter ϵ/n2 (ϵ is the dielectric constant, n is the index of refraction). At large enough values of ϵ/n2 (> 26) the existence of two electron centres and positive vacancies is energetically profitable, and the one‐electron (neutral) centres are absent. Such a situation is apparently realized in chalcogenide glasses where the local lattice distortions near the centres are large and hence the local polarization is large as well.
Propagation of High‐Frequency Electromagnetic Waves in the Voigt Configuration through Samples of Bi at 45, 70, and 300 GHz
Authors: Braune W. , Lebech J. , Saermark K. 
Published: July 2007

AbstractExperimental results on the propagation of very high frequency electromagnetic waves through Bi are presented. The experiments at the frequencies 45 and 300 GHz are performed at 4.2 K on a sample of thickness d = 0.89 mm, and the experiments at 70 GHz are performed at 1.4 K on a sample of thickness d = 1.3 mm. The waves observed propagating through the samples are of the cyclotron wave type. It is pointed out that a satisfactory theoretical understanding of the wave phenomena can only be hoped for if realistic numerical calculations, including all ellipsoids of the Bi Fermi surface and a finite ωτ value, are carried out.
Raman Spectra and Superconductivity of Various Phases of a High‐Tc Superconductor: NbN
Authors: Kaiser R. , Spengler W. , Schicktanz S. , Politis C. 
Published: July 2007

AbstractThe first‐order Raman spectra of β‐, γ‐, and ϵ‐NbN and the defect‐induced first‐order Raman scattering of cubic NbNx are determined. In nearly stoichiometric δ‐NbN the centre of the Raman spectrum after division by the Bose factor is at the same frequency of 150 cm−1 as the centre of the phonon density from neutron scattering. With increasing deviation from stoichiometry the lowest Raman peak in δ‐NbNx due to acoustic phonons shifts to higher frequencies and Tc decreases sharply. This behaviour indicates the existence of phonon anomalies.
Peierls Distortion and Antiferromagnetism in the Quasi‐One‐Dimensional Peierls‐Hubbard Model
Authors: Mertsching J. 
Published: July 2007

AbstractThe one‐dimensional Peierls‐Hubbard model with a half‐filled band is studied in the Hartree‐Fock approximation. Peierls distortion and antiferromagnetism cannot coexist in this approximation, except in the case of special coupling parameters, when the pure Peierls state and the pure antiferromagnetic state are degenerate.
The Effective Magnetic Interactions between Impurity and Conduction Electrons for the Wolff Model
Authors: Spałek J. , Oleś A. M. , Chao K. A. 
Published: July 2007

AbstractA new canonical transformation of a Schrieffer‐Wolff (S‐W) type is applied to the Wolff model at the strong correlation limit to derive an antiferromagnetic (kinetic) exchange interaction between the electrons on the impurity site and the host sites. The problem of the singularity in the original S‐W transformation is removed. The condition for the formation of localized moments is obtained by solving the Green's function with a moment conserving decoupling scheme. If localized moments exist, the high temperature susceptibility, derived in the mean field theory, has a Curie‐Weiss form χ = C/(T + θ) with θ > 0, in agreement with experiments.
A Contribution to the Phenomenological Theory of the Anomalies of the Elastic Constants near a Structural Phase Transition
Authors: Wiszt E. 
Published: July 2007

AbstractRelations for the temperature and frequency dependence of the linear elastic constants for crystals of arbitrary symmetry near a second‐order structural phase transition are derived on the basis of a thermodynamic potential including time and space (one‐, two‐, or three‐dimensional) fluctuations of the order parameter. The calculation is based on a perturbation expansion with respect to the small deformation tensor components and is given in detail for a two‐component order parameter. The results are used for the explanation of the elastic constant anomalies of GMO and Hg2Cl2. The influence of the higher‐order interaction terms above or below the phase transition is investigated with an application to the case of Hg2Cl2.
On Coherent Neutron Diffraction in Nematic Liquid Crystals
Authors: Cvikl B. 
Published: July 2007

AbstractThe differential cross‐section of the coherent neutron diffraction in the nematic phase is derived. It is shown that spontaneous distortions, which enter the theory through the intermolecular part of the structure factor and may be associated with two different diffusive optic soft modes of this phase, influence the neutron diffraction patterns through the correlations in space of the preferred molecular axes. The structure factor is anisotropic and exhibits for 1 Å−1 < Q < 4 Å−1 two distinct peaks depending on the relative orientation of the neutron scattering vector and the uniaxial nematic direction in quantitative agreement with the observations. For 0.4 Å−1 < Q < 1 Å−1 an intense peak is obtained in the calculations.
Electronic Structure and ESR of Ti2+ in Fluorite Type Crystals
Authors: Yunusov N. B. , Zentsov V. P. 
Published: July 2007

AbstractExpressions are given for the spin‐Hamiltonian parameters for an arbitrary transition metal ion in a cubic lattice, according to the multi‐electron ligand field theory, taking into account all possible single‐electron contributions. These expressions together with the results of the electronic structure calculation of the [TiF8]6− complex are used for the calculation of the magnetic parameters of the 47Ti2+ ion in fluorite type crystals MF2 (M = Cd, Ca, Sr, Ba). The calculated values are in satisfactory agreement with the experimental data.
Transverse and Longitudinal Nernst‐Ettingshausen Effect in p‐Te
Authors: Gavaleshko N. P. , Gorley P. N. , Kavyuk P. V. , Solonchuk L. S. , Tarasyuk I. I. , Shenderovskii V. A. 
Published: July 2007

AbstractUsing a variational method, general formulae for the kinetic tensor components describing the galvanomagnetic phenomena in anisotropic semiconductors of the p‐Te type are obtained in terms of matrix elements of different scattering mechanisms for the case of arbitrary magnitude and direction of the non‐quantizing magnetic field. Theoretical and experimental results of the temperature and field dependences of the transverse and longitudinal Nernst‐Ettingshausen effect in p‐Te are compared and discussed.
Influence of Finite Carrier Concentrations on the Electronic Spectrum of a Ferromagnetic Semiconductor
Authors: Matlak M. , Nolting W. 
Published: July 2007

AbstractStarting from the atomic limit‐solution of the s‐f model a diagram technique is used to obtain the one‐particle spectrum of a ferromagnetic semiconductor, valid first of all for low carrier concentration n in the small bandwidth case. It turns out that the conduction band is split, due to the s‐f interaction, into two subbands for every electron spin direction. The lower edge of the lower ↑subband is shifted to higher energies with increasing band occupation explaining herewith recent experiments on EuO. The approximation fulfills the exactly calculable (n = 0, T = 0)‐limiting case.