bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effective interatomic forces from one‐particle crystal field parameters
Authors: Adam S. , Adam Gh. , Corciovei A. 
Published: July 2007

AbstractTheoretical results are obtained for the crystal field coefficients which enable us to develop an approach to the use of the crystal field data for the derivation of information on the effective interatomic forces in crystals. The method is applied to the magnetic Sm3+ ion in SmCo5, and it is shown to provide valuable results both for the effective interatomic potential and for the consistency of various sets of crystal field parameters previously proposed in the literature.
Curie temperature and short‐range atomic order in amorphous ferromagnets
Authors: Maksymowicz A. Z. 
Published: July 2007

AbstractA simple description of amorphous AcB1–c alloys with different coordination numbers of the components of the alloy, ZA = ZB, is discussed. Curie temperature is calculated and mean field approximation results are compared with those obtained by a Green function technique for the Ising model with S = 1/2. The chemical short range order is accounted for and its parameter is calculated for the equilibrium state at temperature T. Fluctuations of coordination numbers and exchange integrals are not considered to get a more clear picture on how the Curie temperature is affected by ZA ≠ ZB. For a diluted ferromagnet with ZB of nonmagnetic atoms smaller than ZA, the Curie temperature increases and the critical concentration for magnetic solution is shifted to lower values. Short range atomic order, which favours A–B pairs, shows opposite tendency.
On the coexistence of superconductivity and itinerant ferromagnetism
Authors: Kolley E. , Kolley W. 
Published: July 2007

AbstractThe interplay of superconductivity and ferromagnetism in an itinerant electron system is described by attractive contact and repulsive Hubbard interactions within a substitutionally disordered tight‐binding model. Functional integral formalism at nonzero temperatures is employed in going over from Grassmann variables to collective Bose fields to derive microscopically the quadratic and quartic terms in the loop expansion of the effective action. The configurational averaging is performed on the mean field level to find out a Landau‐type theory for two biquadratically coupled coherent order parameters. It is proved that the coexistence region for the superconducting and ferromagnetic phases cannot be reached in the percolation limit of AxB1–x alloys. For testing the present method the results of the itinerant and localized spin models are compared.
On the theory of time‐resolved band‐tail luminescence in amorphous semiconductors
Authors: Esser B. 
Published: July 2007

AbstractThe time‐dependent moments of a luminescence band due to radiative recombination within electron‐hole pairs localized in band tail states are calculated. Besides the radiative process a competing non‐radiative process by tunneling of the excited electrons (or holes) to defect centres is assumed. The time dependence of the centre of the band ωc(t) and the linewidth σ(t) are shown to be determined by the time evolution of the tail region from which the electrons effectively recombine at t as well as from the time‐dependent electron‐hole separation in the Coulomb interaction. These two mechanisms act in an opposite way and as a result a non‐monotonous behaviour in both ωc(t) and σ(t) observed experimentally is obtained.
On the diamagnetism of deep impurities in quantized semiconductor films
Authors: Imamov E. Z. , Krevchik V. D. 
Published: July 2007

AbstractThe diamagnetic susceptibility (DS) of one‐electron deep impurity centres (DIC) in quantized semiconductor films is calculated. For electrons in bound DIC states Lucovsky's model with the wave function meeting the boundary conditions on the film surface is taken. For certain values of the impurity centre coordinates the DS dependence on film thickness L with fixed zero range potential capacity is studied. The results of Lucovsky's model for massive semiconductors in the limiting case L → ∞ are obtained.
Study of lattice statics and allied properties of zincblende‐type compound semiconductors
Authors: Singh R. K. , Singh R. D. 
Published: July 2007

AbstractAn interionic potential model is developed which incorporates the effects due to the long‐range Coulomb and three‐body interactions and the short—range overlap repulsion operative up to the second‐neighbour ions, and van der Waals dipole‐dipole and dipole—quadrupole attractions. The use of this potential for comprehensive calculations yields satisfactory prediction of the lattice statics and allied properties of zincblende‐type compound semiconductors. These successes reveal the importance of van der Waals and three‐body interactions in these semiconductors.
Analysis of interionic potentials in alkali chalcogenide crystals
Authors: Jain V. K. , Shanker J. 
Published: July 2007

AbstractAn analysis of the interionic potentials is performed in 14 alkali chalcogenide crystals. New values of the van der Waals potentials are used. Different values of repulsive hardness parameters are introduced for different nearest‐neighbour and next nearest‐neighbour pair interactions. Cohesive energies, bulk modulus and its pressure derivative are calculated for the entire family of crystals under study.
On a ferromagnet coupled to the paramagnetic system: Fluctuations and spin reorientation
Authors: Loos J. 
Published: July 2007

AbstractThe Stratonovich‐Hubbard functional integration method is applied to the isotropic ferromagnet coupled by an antiferromagnetic exchange to a paramagnetic system. Such system represents a simple model e.g. for rare earth iron garnets, The general correspondence between the quantum statistics and the classical description leading to the effective classical Hamiltonian of the fluctuations is outlined. This formalism is applied to the spin‐reorientational phase transition.
Optimization of tosi‐fumi ionic radii for F.C.C. alkali halide crystals
Authors: Damm J. Z. , Chvoj Z. 
Published: July 2007

AbstractOn the basis of several empirical relations between a property (mostly connected with the presence of some point defects) on the one hand and the radii ratio (pj) of the lattice ions and interionic distance (cj) on the other, it is possible to raise the accuracy of Tosi‐Fumi ionic radii values. Pertinent calculations are performed for nine alkali halides (chlorides, bromides, and iodides of sodium, potassium, and rubidium). Using above empirical relations in which accurate cj and pj values (the latter obtained in this work) are introduced, in most instances a very good agreement is ascertained between calculated and experimental values related with appropriate properties.
The band structure of Cd3P2 in the presence of a magnetic field
Authors: Singh M. , Cisowski J. , Wallace P. R. , Portal J. C. , Broto J. M. 
Published: July 2007

AbstractThe band structure of Cd3P2 is presented on the basis of Bodnar's model which is extended by Wallace in presence of magnetic field. The oscillations of the Fermi level with magnetic field are calculated and it is found that the amplitude of the oscillations in Cd3P2 is larger than in Cd3As2. The effect of the so‐called free‐electron term is included in the calculation of the g‐factor and cyclotron effective mass. The correction due to the free‐electron term in the g‐factor is smaller (gf ≪ 2) than anticipated and depends on energy. Another interesting result of the calculation is that there is linear relationship between cyclotron effective mass and energy.
Local partial al DOS in FeAl and AlAl
Authors: Müller Ch. , Ziesche P. 
Published: July 2007

AbstractThe energy eigenvalue results obtained by a linear KKR method for B2 FeAl and an hypothetical B2 AlAl of the same lattice spacing are used to calculate the local partial DOS (densities of states) as well as the corresponding valence‐electron numbers per muffin‐tin sphere (MTS) of these two systems. The comparison of the two different local partial Al DOS indicates that the Al states in the FeAl compound are strongly affected by the antiresonance effect caused by the presence of the resonant Fe scatterer in the neighbourhood. The charge transfer is also discussed in connection with the antiresonance effect.
Nonlinear excitations in superionic crystals near the nonuniform state transition temperature
Authors: Bondarev V. N. , Kuklov A. B. , Rublyov I. S. 
Published: July 2007

AbstractThe amplitude solitonic solutions are investigated on the phenomenological base applied earlier to the superionic conductor (SC) phase transition into the charge density wave (CDW) state. These solitons ‐ long range CDW modulations ‐ can be produced by an external electric field in the SC symmetrical phase. For sufficiently strong fields such solitons represent the unstability channel with respect to the CDW formation throughout the crystal above the transition point. Due to the additional charge redistribution the mentioned solitons can be observed experimentally.
On the problem of electron localization in a two‐dimensional system
Authors: Bonch‐Bruevich V. L. , Mironov A. G. 
Published: July 2007

AbstractRenormalization group method is extended to take account of the correlation between the energy levels. It is shown that in a d = 2 system, as contrasted to d = 1 and d = 3, all or not all levels are localized depending upon some dynamical properties of the system.
Temperatur‐ und magnetfeldabhängigkeit einer transversalen schallgeschwindigkeit im tetragonalen paramagneten mit dem gesamtdrehimpuls J = 1
Authors: Ulner J. 
Published: July 2007

AbstractIm Rahmen der Theorie der rotationsinvarianten magnetoelastischen Wechselwirkungen wird die Temperatur‐ und Magnetfeldabhängigkeit einer transversalen Schallgeschwindigkeit im tetragonalen J = 1‐Paramagneten bestimmt. Dabei wird eine Green‐Funktionsmethode formuliert, die die Eigenschaften des Gesamtdrehimpulses exakt berücksichtigt. Es wird der Fall eines kooperativen Jahn‐Teller‐Überganges diskutiert.
Luminescence of high density electron‐hole plasma in CdS and CdSe in a wide temperature range
Authors: Yoshida H. , Shionoya S. 
Published: July 2007

AbstractTime‐resolved spectra of the spontaneous luminescence of the high density electron‐hole plasma (EHP) in CdS and CdSe are observed in a wide range of temperature which is surely higher than the calculated critical temperature for electron‐hole liquid formation, in order to carry forward discussion on dynamic nature of the EHP previously observed in 4.2 K experiments. Spectra in the late stage are analyzed, and obtained values of the reduced bandgap energy and chemical potential are compared with those theoretically calculated for higher temperatures. The aspects of the change of the spectral shape in the late stage are hard to understand. Unfortunately, no clear conclusion is drawn on the nature of the EHP produced at 4.2 K. The only thing one can say is that the condensed electron‐hole liquid state, which is in equilibrium with the exciton state, is not realized.
Mean‐square displacement and Lindeman's criterion for melting of alkali metals
Authors: Soma T. , Kagaya H.‐Matsuo , Nishigaki M. 
Published: July 2007

AbstractThe temperature dependence of the mean‐square displacement for alkali metals is quantitatively calculated from first principles. Lindeman's criterion for melting obtained is nearly constant for the five alkali metals. The Debye temperature at higher and lower temperatures is also estimated using Debye's model.
Analysis of the equation of state of lithium and sodium halides
Authors: Shanker J. , Singh K. 
Published: July 2007

AbstractA theoretical analysis of the equation of state is performed for the halides of lithium and sodium. The variation of volume with pressure is calculated using seven different potential functions for the short‐range overlap repulsive energy. The van der Waals dipole‐dipole and dipole‐quadrupole interactions derived from thevariational method are taken into account. The results obtained are compared with available experimental data. In most of the crystals studied, the Varshni‐Shukla exponential potential for the repulsive energy gives the best agreement with experimental data for the equation of state.
Thermally‐stimulated excitation of electrons from deep traps of insulators in electric fields
Authors: Köster H. , Iassievich I. N. , Hübner K. 
Published: July 2007

AbstractAn analytic expression for the probability of thermal activation of electrons trapped in deep defect states of an insulator is derived taking explicitly into account an electric field and lattice vibrations. From the activation probability a detrapping current intensity is calculated, which is in good agreement with corresponding experimental results obtained, for example, by means of the thermally stimulated electron emission (TSEE). In this way, for the TSEE effect a possible microscopic explanation is found for the first time.
EPR of iron‐boron centres in silicon
Authors: Gehlhoff W. , Segsa K. H. 
Published: July 2007

AbstractThe EPR spectra of one type of iron‐boron centres detected in low‐resistivity B‐doped p‐silicon after iron doping are investigated in detail. The spectra are characterized by a dominating zerofield splitting and a resolved SHF structure due to the interaction with the boron isotopes and arise from interstitially incorporated Fe+ ions adjacent in 〈111〉 directions to B− ions on substitutional sites.
Electronic structure and stability of amorphous PdSi alloys
Authors: Buschow K. H. J. , Eifert H.‐J. , Elschner B. 
Published: July 2007

AbstractAmorphous alloys Pd1−xSix near x = 0.2 doped with small amounts of Gd are prepared by melt spinning. The g‐shift, the residual linewidth, and the thermal broadening of the EPR linewidth are determined. Doped and undoped amorphous alloys are also investigated by means of differential scanning calorimetry. Values are reported for the glass temperatures, crystallization temperatures, heat of crystallization, and heat of activation. It is shown that electronic properties of amorphous alloys are unlikely to exert much influence on the thermal stability of these alloys.
Divacancy binding energy in F.C.C. metals
Authors: Kornblit L. 
Published: July 2007

AbstractDivacancy binding energies Eb2V in f.c.c. metals are calculated with aid of an atomistic‐continual model used earlier for single vacancy formation energy calculations. The main part of Eb2V stems from the first nearest‐neighbor (Inn) atomic environment of the divacancy. The outer region which is treated as an elastic continuum contributes a relatively small part.
The use of an iteration method for calculating the potential energy of nonhomogeneous dielectrics
Authors: Fokin A. G. 
Published: July 2007

AbstractA method of solving linear boundary‐value problems is developed, based on the interpretation of the problems in terms of functional analysis. The potential energy is presented in the form of the functional, which can be generally expanded into a series. The boundaries are obtained, enclosing the exact value of the potential energy.
Diffusion of Frenkel excitons in anisotropic crystals
Authors: Glushko E. Ya. , Efremov N. A. 
Published: July 2007

AbstractThe temperature dependence of the diffusion tensor Dik(T) of coherent excitons in anisotropic molecular crystals is considered. The influence of such exciton energetic band peculiarities as effective mass tensor anisotropy and nonanalyticity of exciton energy on the dependence Dik(T) is analyzed. It is shown that the dependence D ∼ T−1/2, which is characteristic of isotropic crystals, is retained only at weak anisotropy of the effective mass tensor mmax/mmin ≈︁ 1 with no regard for nonanalyticity. At the same time, at great values of the nonanalytic part of the exciton energy the diffusion tensor component dependences vary from Daa ≈︁ Dcc ∼ T−1 ≪ Dbb ∼ T−2 at weak anisotropy of the effective mass tensor to Daa ≈︁ Dcc ≈︁ const ≪ Dbb ∼ T−3/4 at strong anisotropy.
The 3/2 kT problem in the low‐temperature polaron mobility theories
Authors: Peeters F. M. , Devreese J. T. 
Published: July 2007

AbstractThe linear de mobility of Fröhlich polarons is studied in the limit of small electron‐phonon coupling and low temperature. The well‐known discrepancy with a factor of 3/2kT/hωLO between the results appearing in the literature is understood in the light of an interchange of the limits limits lim lim.
Impurities and electron localization in V2O5 crystals
Authors: Grunin V. S. , Patrina I. B. , Zonn Z. N. 
Published: July 2007

AbstractV2O5 crystals doped with different impurities of the Mn+ (n = 1 to 6) type are investigated by the EPR method. It follows from the experiment that all the paramagnetic defects are connected with the impurities present in the crystals. The main paramagnetic centre in V2O5 is an electron localized on two 51V nuclei. There is no local compensation of its charge and so it easily destroys in the course of oxidation. It is shown by hyperfine structure investigation that the electron states are localized in a wide temperature range (4.2 to 290 K). The substitutional impurity tends to occupy the vanadium positions near the VV pair. A complex paramagnetic centre is created with electron density distribution dependence on the donor‐acceptor characteristics of the cations. This results in the nonequivalence of the electron interactions with different vanadium atoms, in different values of the HFS constants for differently doped crystals, and in different valency of the impurity cations. Centres of this type are locally compensated and therefore stable to oxidation or reduction.
Second‐order quadrupole shift in the incommensurate structures of Rb2ZnBr4 and Rb2ZnCl4
Authors: Aleksandrova I. P. , Grande S. , Moskvich Yu. N. , Krieger A. I. , Koptsik V. A. 
Published: July 2007

AbstractThe angular dependences of second‐order 87Rb (1/2 → −1/2) shift in the incommensurate phases of Rb2ZnBr4 and Rb2ZnCl4 are interpreted and EFG‐tensors at the special points of the displacement profile are determined. The EFG‐tensor of I‐structure is described in the approach of perturbance theory: Vij{S} = V{S} + ΔV{S} where the EFG‐tensor of the paraelectric phase is taken as zero‐approximation. It is most important that the form of “modulation correction” tensor ΔVij is not arbitrary. The symmetry properties of one‐dimensional incommensurate modulated atomic chain determine the selection rule for the non‐zero components of the tensor of modulation corrections. The existence of supersymmetry for structurally incommensurate systems follows from the presented NMR‐experiments. The abstract symmetry conservation law at commensurate‐incommensurate transition seems to be demonstrated in this experiment.
Effect of varying the orientation of a quantizing magnetic field on the effective electron mass in degenerate tetragonal semiconductors
Authors: Chakravarti A. N. , Ghatak K. P. , Ghosh K. K. , Mukherjee H. M. 
Published: July 2007

AbstractAn attempt is made to investigate the effects of varying the orientation of a quantizing magnetic field on the effective mass in tetragonal semiconductors. It is found, taking n‐Cd3As2 as an example, that the crystal‐field splitting results in different effective masses at the Fermi level corresponding to different magnetic sub‐bands. These effective masses are found to be significantly influenced by the orientation of the magnetic field with respect to the c‐axis. This behaviour is further noted to be strongly dependent on the carrier concentration but is relatively much less sensitive to changes in the magnetic field strength.
On the theory of the nonlinear acousto‐optical effect in semiconductors
Authors: Cam Hoang Ngoc , Van Hieu Nguyen , Tan Ha Vinh 
Published: July 2007

AbstractThe modulation of the dielectric susceptibility of direct band gap semiconductors due to the interaction with sound waves is considered up to second order of the deformation tensor. The role of the Coulomb interaction between electrons and the holes, i.e. that of exciton states with discrete and continuous energies, is taken into account.
On the Brillouin zone integration
Authors: Reser B. I. 
Published: July 2007

AbstractA brief and simple description is given of three new methods of integration in the Brillouin zone: direct, ray, and hybrid tetrahedron, proposed by Chen, McDonald et al. These methods are analyzed in detail in application to the calculation of the density and number of states of s.c., b.c.c., and f.c.c. crystals using tight‐binding and empty lattice models. It is shown that all the methods considered exhibit a high accuracy: several hundred initial k points in the irreducible part of the Brillouin zone with not very complicated dispersion relations make it possible to calculate such a quantity, as the density of states, with an average error of less than 1%. The hybrid tetrahedron method is proved to be simpler and many times more effective than the other two methods. Only with dispersion relations close to isotropic is the ray method preferable.
Thermal expansion coefficient of alkali metals
Authors: Soma T. , Kagaya H.‐M. , Kimura Y. 
Published: July 2007

AbstractThe thermal expansion of alkali metals is investigated using a local Heine‐Abarenkov model potential in the perturbational method. The mode Grüneisen parameters and the temperature‐dependence of both the mean Grüneisen constant and the thermal expansion coefficient are calculated, and the obtained results are quantitatively in good agreement with the experimental data.
Thermoelectric properties of GeTe at high hydrostatic pressure up to 8.5 GPa and its valence‐band structure
Authors: Khvostantsev L. G. , Sidorov V. A. 
Published: July 2007

AbstractThe thermopower and the relative electrical resistance of rhombohedral α‐GeTe and orthorhombic γ‐GeTe polycrystalline samples with hole density between 3.9 × 1020 and 2 × 1021 cm−3 are measured under hydrostatic pressure up to 8.5 GPa at room temperature. The phase transition of α‐GeTe to the cubic rocksalt structure (β‐GeTe) reported earlier at 3.5 GPa under nonhydrostatic pressure is not observed up to 8.5 GPa. Orthorhombic γ‐GeTe also exhibits no phase transition. The pressure dependences of the thermopower provide support for the multiple valence‐band model of GeTe.
Nonlinear magneto‐optical phenomena of the third harmonic in semiconductors
Authors: Stramska H. 
Published: July 2007

AbstractThe calculations are carried out starting from the Boltzmann equation. The Faraday rotation and ellipticity of the third harmonic in the current density, are associated with the energy dependence of the momentum relaxation time for a parabolic band and with the nonparabolicity of the band for a constant relaxation time. The present results predict a large enhancement due to resonance at high magnetic fields. It is shown that the magneto‐optical effects have an oscillatory region.
Satellite structure of ZnO and Zn(II) halides studied by X‐ray photoelectron spectroscopy
Authors: Scrocco Marisa 
Published: July 2007

AbstractThe satellite structure in the X‐ray photoelectron spectra of Zn(II) halides and ZnO is examined, particular attention being paid to the 3p, 3s metal subshells and the valence region. The nature of the phenomena giving rise to these satellites and their relative importance in each spectral region, is discussed with reference to known theoretical results.
A binary ferromagnetic alloy with magnetic moments dependent on local environment. I. The Jaccarino‐Walker Model in the effective field approximation
Authors: Zaborov A. V. , Medvedev M. V. 
Published: July 2007

AbstractA binary ferromagnetic alloy, in which the magnetic moments depend on their local chemical environment in a step‐like manner (the Jaccarino‐Walker model), is considered. It is assumed that Heisenberg exchange interactions of the nearest neighbours are responsible for the ferromagnetic ordering of these magnetic moments. Both, the Curie temperatures versus concentration and the percolation thresholds of the existence of the long‐range magnetic order are investigated for different variants of dependences of both the magnetic components on their local environments. The spin‐wave spectrum is analyzed as well.