bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anomalous Mössbauer Lineshapes in the Magnetically Ordered Ga2O3–Fe2O3 System
Authors: Nagarajan R. , Srivastava J. K. 
Published: July 2007

AbstractMössbauer measurements show that an incomplete annealing of the magnetically ordered Ga2O3–Fe2O3 system gives rise to anomalous Mössbauer spectra which are characterised by an enhancement in the intensity (or percentage absorption) of their central portions as compared to the intensity of outer absorption peaks. Measurements carried out in an external magnetic field confirm that the observed anomalous Mössbauer lineshapes are due to ionic spin fluctuations (either due to the motion of individual spins, i.e. electronic relaxation effects, or due to the collective motion of large number of spins in a small region of material, i.e. superparamagnetic effects) and are not a result of any distribution of hyperfine field or the presence of critical superparamagnetism in the incompletely annealed solid solutions.
Dynamical Response of Electrons in GaAs at 300 K
Authors: Brauer M. 
Published: July 2007

AbstractNumerical calculations are made on the time response of the high‐field electron distribution function at T = 300 K in GaAs both for instantaneously and periodically varying electric fields. According to Rees the method of calculation is an iterative process due to Kellogg for solving a homogeneous Fredholm integral equation of the second kind derived from the Boltzmann equation. The time evolution of the average drift velocity, the mean energy of the electrons in the central valley, and the fraction of electrons in the satellite valleys is presented for an instantaneous application E(t) = E · θ(t) of the electric field. Finally the time dependence of the average drift velocity and the satellite valley population fraction is calculated for a sinusoidal electric field E(t) = Eac × sin ωt with Eac = 5 kV/cm and ω = 2.2 × 1011 rad/s. The results obtained are discussed, taking into account the band structure and the effective scattering processes.
Numerical Results of the Hubbard III Approximation for Arbitrary Values of the Correlation Energy and the Electron Density (with Application to Disordered Alloys)
Authors: Kammler F. , Elk K. 
Published: July 2007

AbstractFor the Hubbard model the density of states and the damping are calculated numerically for arbitrary values of U and n. The magnetic properties of the ground state are studied by a self‐consistent calculation of the magnetization m. It is shown, that the ferromagnetic state is unstable for each value of U and n. Using the same procedure binary alloys are considered, too.
The Boson Field Analysis of the Critical Temperature Region in Ferromagnets
Authors: Tošić B. S. , Marinković M. M. , Berar S. 
Published: July 2007

AbstractA new method is proposed which makes it possible to apply the boson picture to ferromagnetics at high temperatures. A result of such an approach is the appearance of an additional level that leads to a phase transition from the ferromagnetic to the antiferromagnetic phase which takes place in the majority of rare earths. It is also shown that the boson picture of the ferromagnetics yields a richer physical content than the other, usual ones. Its main consequence leads to the conclusion that the Heisenberg model of ferromagnets works best to weak ferromagnetics (mainly rare earths).
Effect of Crystal Field on the Inelastic Neutron Scattering Cross‐Section
Authors: Sugawara K. 
Published: July 2007

AbstractThe magnetic inelastic scattering of neutrons by paramagnetic rare‐earth compounds where the rare‐earth ion has a substantial crystal‐field splitting is studied theoretically. Using the time‐dependent spin correlation functions, the effects of the crystal‐field and exchange to the first and second moments of inelastic neutron scattering cross section are investigated. The results are applied to the singlet ground‐state Pr‐ and Tm‐compounds. We also discussed the relationship between the temperature dependence of the intensity of quasi‐elastic scattering and those of longitudinal relaxation rates of NMR and EPR.
The Effects of Coordination Polyhedron Structure on Rare‐Earth Ion Spectra
Authors: Korolkov V. S. , Makhanek A. G. 
Published: July 2007

AbstractInvestigations are made of some regularities in the position of Stark components and a number of conclusions are drawn on the nearest surrounding structure rare‐earth (RE) ions. Since the splitting of the J‐manifold is generally defined by the overlap of RE ions and ligand orbitals, it is possible to establish a relation between the phenomenological crystal field parameters \documentclass{article}\pagestyle{empty}\begin{document}$ B_{t_p \overline {r^t}} $\end{document} (CFP) and the structure of the nearest surrounding. It is important that the various multipolarity CFP (t = 2, 4, 6) in the overlap model depend identically on R while their values in the CF theory are proportional to \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {r^t } /R^{t + 1} $\end{document}. The dependence on the ligand angular coordinates is similar for the two models.
Raman Scattering from Tunnelling and Hindered Rotational States of CN− Molecules in KCl
Authors: Durand D. , Luty F. 
Published: July 2007

AbstractThe low lying tunnelling and hindered rotational states of dilute (≈ 10−4) systems of substitutional CN− ions in KCl are studied by Raman techniques. The tunnelling splitting of the ground state could be directly observed as a resolved side‐band structure of the CN− stretching vibration. The observed splitting is in quantitative agreement with the previously derived value for the tunnelling splitting, while the appearance of this splitting only in the T2g scattering geometry confirms definitely the 〈111〉 dipole model. Hindered rotational structure (in the 10 to 30 cm−1 range), which is partially resolved, is detected, both in the low energy and stretching‐side‐band spectrum in Eg and T2g symmetry. The observed Raman data can be fitted to the Raman positions and intensities calculated by Beyeler, using the V4 + V6 Devonshire model parameters derived from high resolution IR work.
Crystal Field Parameters for Gd3+ in Gd2(MoO4)3
Authors: Guttel C. , Antic E. , Caro P. E. 
Published: July 2007

AbstractThe absorption spectrum of Gd3+ in orthorhombic Gd2(MoO4)3 single crystal is measured at temperatures from 4 to 453 K. Nd3+ (10% and 50%) and Dy3+ (23%) substituted to Gd3+ give rise to little shifts of the absorption spectrum. The positions in the energy scale of the Stark components of the 6P levels of the 4f7 configuration of Gd3+ are obtained. A parametric computation of part of the C2v crystal field parameters yields the following values: B = − 222, B = +489 cm−1. Ground state 8S7/2 zero field splitting is predicted as a result of the calculation.
Comments on the Static Dielectric Function of Jellium
Authors: Brosens F. , Lemmens L. F. , Devreese J. T. 
Published: July 2007

AbstractThe equation of motion for the Wigner distribution function in a homogeneous electron gas, linearized to first order in the applied external field, and decoupled using the Hartree‐Fock prescription, rigorously describes the dynamical exchange effects in the dielectric response to a ‐weak perturbation. This equation of motion can approximately be solved with a variational principle, and a trial solution for the Wigner distribution function can be found, yielding a density that exactly satisfies its equation of motion. The dielectric function ϵvar obtained in this way thus includes dynamical exchange interactions. Comparing ϵvar with the dielectric function ϵit obtained from an iterative procedure, where exchange effects are supposed to be small compared to the Hartree terms, it turns out that ϵit provides the terms to order e4 in the geometric progression of ϵvar in powers of e2. In the static limit ϵit is the dielectric function calculated by Geldart and Taylor from a diagrammatic expansion. Thus a theoretical justification is given for Sham's approximation that the static susceptibility including exchange is obtained by considering the susceptibility from the diagrammatic expansion as the first two terms in a geometric progression.
Localized States on Imperfections and Red Shift of the Absorption Edge in Some Ferromagnetic Semiconductors
Authors: Čápek V. 
Published: July 2007

AbstractA theory is presented for the red shift of the absorption edge of some ferromagnetic semiconductors as being due to localized electronic states on lattice imperfections influenced by the usual s–d coupling. A good correspondence with the experiment on some chromium chalcogenide spinels is obtained.
Infrared Absorption by an Optical Polaron in a Magnetic Field
Authors: Huybrechts W. J. 
Published: July 2007

AbstractThe infrared absorption by an optical polaron in an external magnetic field is discussed for weakly polar semiconductors at low temperatures. The broadening of the cyclotron resonance and the anomaleous behaviour of the cyclotron mass are evaluated to first order in the electron‐phonon coupling using a well‐known perturbational approximation.
The Resonant States of the Ti(d2) Impurity in CdSe
Authors: Kocot K. , Baranowski J. M. 
Published: July 2007

AbstractOptical and electrical investigations show that Ti introduces a shallow donor in CdSe. The character of this donor is determined by the well localized 3d2shell of the Ti impurity substitutional on cadmium sites. The energy position of the Ti(d2) level depends on temperature and hydrostatic pressure. It is demonstrated that at high temperatures the Ti (d2) ground state becomes degenerate with the conduction band of CdSe. It is also shown that the excited 3T1 (F) and 3T1(P) states of the Ti (d2) are resonant states. Autoionization of the excited Ti (d2) impurity is observed in photoconductivity measurements.
Quantum Theory of the Order–Disorder Transition Energy in AuCu3
Authors: Kozlov E. V. , Emelyanov V. N. , Antonov V. A. 
Published: July 2007

AbstractThe stability conditions of the short‐ and long‐range orders are formulated and numerical calculations are made of the order‐disorder heat of transition as well as the total ordering energy of a AuCu3 solid solution having the Ll2 superstructure.
Coherent Ladder Approximation for the Random Hubbard Model
Authors: Kolley E. , Kolley W. 
Published: July 2007

AbstractDynamical effects of the electron–electron interaction in binary alloys with off‐diagonal disorder are described in a self‐consistent theory obtained by unifying a local ladder approximation for the random Hubbard model and a modified CPA. Numerical results are presented for partially averaged densities of states, self‐energies which fulfil the Luttinger theorem, and effective two‐particle vertices. The totally averaged density of states exhibits tails with strongly damped correlation humps.
Magnetooptical Investigation of Hg1‐xCdxTe Mixed Crystals II.Semiconducting Configuration and Semimetal → Semiconductor Transition
Authors: Guldner Y. , Rigaux C. , Mycielski A. , Couder Y. 
Published: July 2007

AbstractAn investigation is made of the interband magnetoabsorption at photon energies 120 to 370 meV on semiconducting Hg1‐‐xCdxTe alloys (x ≦ 0.3). Magnetooptical spectra obtained in the Voigt (ϵ ∥ H) and Faraday (σ+, σ‐) geometries are interpreted in the framework of the Pidgeon and Brown model. The band parameters are estimated for each composition by fitting the transition energies. First observations are reported of polaron effects inducing interband magnetooptical anomalies. By extending the magnetoabsorption measurements to alloys of very small interaction gaps, the evolution of Γ8, Γ6 levels in the region of the semimetal → semiconductor transition is described.
The One‐Dimensional Fourier Transform of Compton Profiles
Authors: Sciiülke W. 
Published: July 2007

AbstractTheorems on the one‐dimensional Fourier transform of directional Compton profiles are given within the frame of the one‐electron approximation. The theorems relate the one‐dimensional Fourier transform of Compton profiles with the three‐dimensional Fourier transform of the momentum density, with the off‐diagonal elements of the first‐order density matrix, with the translation invariance of the lattice, and with the density of Bloch k‐states (Fermi surface) respectively. Possible applications of these theorems are discussed and demonstrated by means of the Fourier transform of experimental Compton profiles of Si and Li.
On the Polymorphic Phase Transition in Alkali Halides
Authors: Charabarti S. K. 
Published: July 2007

AbstractEarlier calculations of the equation of state and phase transition data at 298 K for a potassium chloride crystal are extended to include the other alkali halides. It is shown that both the elastic and phase transition data are well reproduced by the three‐body potential model (TBPM). Since the calculations tend to become lengthy, a simpler procedure of calculating the equation of state and transition pressure with the help of the Murnaghan's equation is also suggested. The procedure gives reasonably good agreement with experimental results.
Diffusion Correlation in Random Primitive Cubic Alloys
Authors: Buin H. J.De , Bakker H. , Van Der Mey L. P. 
Published: July 2007

AbstractCorrelation effects for diffusion in random cubic alloys are calculated by Monte Carlo computations. Using two independent models the parametersfB,fA,fv, the correlation factors, and ‐ tB, the net probability that a B‐tracer will return to its original lattice position, are obtained and analyzed. Evidence is presented that the relation, fB = (1+‐tB)‐ /(l − tB), is not strictly valid in these alloys where symmetry around the vacancy jump vector does not normally exist. However deviations are not large for realistic vacancy‐atom exchange frequencies WA/WB> 0.1).
Spin‐dependent recombination at exchange‐coupled dislocation centres in silicon
Authors: Wosiński T. , Figielski T. 
Published: July 2007

AbstractThe recent experimental results on spin‐dependent recombination at dislocations in Si are reviewed. A theoretical model including an exchange interaction between unpaired electrons in the dislocation core is proposed. The numerically calculated exchange integral appears to have a positive value. The model presents a dislocation as consisted of segments of exchange‐coupled paramagnetic centres. The magnetization of the segments, calculated in Ising approximation is compared with the experimental results.Kürzliche experimentelle Ergebnisse von spinabhängiger Rekombination an Versetzungen in Si werden erneut diskutiert. Ein theoretisches Modell wird vorgeschlagen, das Austauschwechsel‐wirkung zwischen ungepaarten Elektronen im Kern der Versetzung annimmt. Das numerisch berechnete Austauschintegral scheint einen positiven Wert zu haben. Das Modell liefert eine Versetzung, die aus Abschnitten von Austausch‐gekoppelten paramagnetischen Zentren besteht. Die Magnetisierung der Abschnitte, die mit der Ising‐Näherung berechnet wird, wird mit den experi‐mentellen Ergebnissen verglichen.
The “extra” phase transition in TTF‐TCNQ
Authors: Phillips J. C. 
Published: July 2007

AbstractHigh‐resolution heat capacity data show an “extra” phase transition at 46 K in TTF‐TCNQ powders in addition to the five phase transitions observed in bulk samples between 38 and 54 K. The “extra” phase transition in powders can be explained as a surface phase transition which corresponds to the bulk phase transition at 48 K. In powders the latter is shifted to 49 K by ferroelastic interactions between the “bulk” phase in grain interiors and the compressed surface phase.
Optical properties of cuprous halides in the 4 to 30 eV range
Authors: Lewonczuk S. , Gross J. G. , Khan M. A. , Ringeissen J. 
Published: July 2007

AbstractThe reflection spectra of CuCl, CuBr, and CuI monocrystals are measured in the 4 to 30 eV range, mainly with synchrotron radiation of ACO in Orsay. The band structure of CuCl and CuBr are calculated. The highest valence band is predominantly d‐like, as already stated, the second band is p‐like. Information about the band structure is also obtained by recent photoemission measurements which permit an evaluation of the densities of valence states. A disagreement appears when the results of the two methods are compared, in particular for the shape of the second valence band. The experimental features are discussed taking into account theoretical and photoemission results.
A New Approach to the Theory of X‐ray Spectra of Metals with Allowance for the Finite Lifetime of the Deep Hole
Authors: Sokolov O. B. , Grebennikov V. I. , Turov E. A. 
Published: July 2007

AbstractThe effect is analyzed of the deep hole forming on the inner level during X‐ray transition on the form of the corresponding emission and X‐ray photoelectron spectra of metals. The intensity of both the types of spectra is calculated in one common approach within the framework of the theory of scattering of the exciting photon on the electronic metal system. A generalization of the Wigner‐Weisskopf theory of radiation damping of excited atomic state is proposed for the case of a many‐particle system. The new approach permits to make allowance for the effect of the process of readjustment of valence electrons on the rate of radiation decay. It is shown that these phenomena can be taken into account formally if an effective non‐Hermitean Hamiltonian of a definite type is introduced into the theory. The general formulae obtained permit comparison of the results of different approaches in the theory of the spectra under investigation. The spectra can be analyzed numerically not only near the excitation threshold but also over the whole energy interval on the basis of simple models.
Magnetic susceptibility anisotropy of holes in tellurium
Authors: Vorontsov S. A. , Dolgopolov D. G. , Poltoratskii V. I. , Svechkarev I. V. 
Published: July 2007

AbstractAn expression for the spin contribution to the magnetic susceptibility anisotropy of holes in tellurium is derived. The total hole susceptibility anisotropy including spin and orbital terms is calculated with scattering taken into account. The complete quantitative description of the experimental data for hole concentrations of 3.5 × 1016 ≦ n < 3.5 × 1018 cm−3 and T = 4.2 K is obtained by means of selection and more precise definition of the spectrum parameters which determine the spin contribution. The discrepancy between calculated and experimental temperature dependences of the hole magnetic susceptibility anisotropy at temperatures above 60 K appears to be due to the thermal variation of the spectrum parameters.
Frequency spectra of disordered chains with short‐range order
Authors: Wu Shi‐Yu , Cocks J. A. , Chiu V. 
Published: July 2007

AbstractThe frequency spectra of five binary chains with equal atomic concentrations but various strengths of short range order are computed using Wu's approximate method. The configurations associated with the pseudolocalized resonance and localized modes are identified and the probabilities of their appearance are correlated to the short range order parameter Pij.
Resonance scattering of X‐rays in metals
Authors: Sokolov O. B. , Grebennikov V. I. , Turov E. A. 
Published: July 2007

AbstractA theory is proposed of resonance scattering of X‐ray radiation on the electronic system of a metal which reasonably takes into account the damping of the intermediate states with a hole on the inner level. In virtue of the formulae obtained for the cross‐section of photon scattering, expressions are derived for absorption and threshold emission spectra. Adequate allowance for the finite lifetime of the deep hole permits the description of the re‐emission process. Investigated are the emission spectra arising in the event of transition of an electron between the inner levels of the atom of the metal when excited by a radiation whose frequency is less than the ionization threshold of the corresponding level.
On the theory of parametric excitation in quantum electron–phonon systems
Authors: Anh Vo Hong , van Trong Nguyen 
Published: July 2007

AbstractThe problem of parametric excitation of electromagnetic vibrations of a quantum electron‐phonon system is studied using a formalism based on the equation of motion for the quantum distribution function of an electron gas interacting with phonons in the presence of high‐intensity radiation field and the complete system of Maxwell equations. Calculations of the growth rates and the threshold values of the external electric field E0 are presented for both, uncoupled electron and electron‐phonon systems in different regions of wave number κ for κ ‖ E0 as well as for κ ⊥ E/0.
Asymptotic oscillations of the radial distribution function in a quasi‐crystalline model of liquids
Authors: Medvedev N. N. , Naberukhin Yu. I. 
Published: July 2007

AbstractThe radial distribution function (RDF) behaviour at large R in a quasi‐crystalline model of liquids (crystal lattice with lattice sites smeared out by the Gaussian distribution) is studied by numerical calculations. RDF asymptotic oscillations are found to be describable by the Fisher formula obtained from general statistical laws, if the model is based on b.c.c. and f .c.c. lattices, and not to be describable by this formula for hexagonal close packing. It is also established that the parameters of experimental RDF asymptote for liquid argon differ from those for the three above‐mentioned lattices.
On F‐ and FH‐centres in cesium halides
Authors: Vandekhaeghe A. , Jacobs G. 
Published: July 2007

AbstractFg‐centres are formed in CsI doped with foreign halogen ions, by irradiation in the F‐band at 180 K. They are observed in CsI:Br−, CsI:Cl−, and CsI:F−. The lifetime of the relaxed excited state of the F‐centre in pure CsI and of the FH‐centre is determined by measuring the repopulation of the ground state after depletion with laser light. The results are τR = 3 μs for the F‐centre in CsI, 360 ns for CsI: Br−, 400 ns for CsI: Cl−, 290 ns for CsI: F−. The luminescence decay time of the F‐centre in CsCl is found to be 2 μs, the relaxed excited state lying 0.07 eV under the conduction band. The results on the FH‐centre suggest that the lowest emitting level is 2s with a large admixture of 2p character. Simultaneously with the formation of FH‐centres, new absorption bands appear in the M‐band region, possibly due to MH‐centres.
Wave‐vector dependence of the electron energy losses of PbS, PbSe, and PbTe
Authors: Büchner U. 
Published: July 2007

AbstractThe wave‐vector(q‐)dependence of electron energy losses of cubic PbS, PbSe, and PbTe up to q‐values near the first Brillouin zone boundary and up to energies of 40 eV is given. Anisotropic effects of the derived energy loss functions Im [−ε(ω, q(ijk))]−1 and dielectric functions ε2(ω, q(ijk))[(ijk) = (100), (110), (111)] are observed and discussed in terms of present band structure calculations.
Ladungszustand von Bor in Boriden der Übergangsmetalle
Authors: Aleshin V. G. , Serebryakova T. I. , Kharlamov A. I. 
Published: July 2007

AbstractMit der Methode der Röntgen‐Photoelektronen‐Spektroskopie werden die Bindungsenergien von Rumpfelektronen in einer Gruppe von Boriden der ersten Übergangsperiode gemessen. Es wird gezeigt, daß in Boriden der Metalle, die am Anfang der Periode stehen, die Elektronendichte an den Bor‐Atomen größer und in Boriden der Metalle, die am Ende der Periode stehen, kleiner ist als die Elektronendichte in reinem Bor. Das Übergangsmetall ist in alien Fällen ein Donator. Die beobachtete Änderung des Ladungszustandes der Bor‐Atome befindet sich im Einklang mit den vorhandenen Vorstellungen über den Typ der chemischen Bindung in Boriden.