bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic States of a Binary Ferromagnetic Alloy with Competition of Easy‐Axis and Easy‐Plane Single‐Ion Anisotropies
Authors: Lukanin A. I. , Medvedev M. V. 
Published: July 2007

AbstractThe magnetic phase diagrams of a binary ferromagnetic alloy with positive nearest‐neighbour exchange interactions and competing easy‐axis and easy‐plane single‐ion anisotropies are investigated in the molecular field approximation, especially the possibility of random asperomagnetic and fan states at low temperatures. The spontaneous magnetization vectors for these states are aligned along the crystallographic axes and the transverse projections of atomic spins are frozen in an incoherent spin‐glass like manner.
Valence Bands of the Cu—III—VI2 Chalcopyrites Studied by Photoemission Spectra, X‐Ray Emission Spectra, and Electronic Structure Calculations
Authors: Neumann H. , Bullett D. W. , Sommer H. , Tomlinson R. D. , John W. 
Published: July 2007

AbstractUltraviolet and X‐ray excited photoemission spectra and Cu Kβ5 X‐ray emission spectra are used to measure the valence band density of states in CuGaTe2 and CuInTe2. In both compounds the density of states exhibits five structures which are ascribed to Cu 3d—Te 5p hybridized states, Ga 4s/In 5s—Te 5p bonding states, and Te 5s states. The valence band density of states of all Ga‐and In‐containing Cu—III—VI2 is calculated in an atomic orbital basis with the noble metal d states explicitly included. The agreement between theory and experiment is good for CuGaTe2 and except the In 5s—VI p bonding states also for the CuInVI2 chalcopyrites. Larger discrepancies between theory and experiment are found for CuGaS2 and CuGaSe2.
Position Dependence of Channeling Stopping Power
Authors: Pathak A. A. 
Published: July 2007

AbstractThe position dependence of energy loss rates of MeV α‐particles along (110) and (111) planar channels of silicon single crystals is calculated. The effective electron density responsible for stopping power is estimated by averaging the spherically symmetric radial charge densities corresponding to individual shells of atoms along the relevant planes. This averaging procedure is similar to that adopted in finding the continuum potential, using superposition of interatomic potentials; except that here each individual shell is considered and the contribution is added after planar averaging. The results thus obtained are compared with the recent experimental results of Moak et al.
A Correlation between the Spectral Location of the Absorption Bands Due to the Localized Centers and the Lattice Constant in Alkali Halide Crystals. Anionic Impurity Centers with S2‐Configuration and F Center which Have Cubic Symmetry
Authors: Shimanuki S. , Nishimaki N. 
Published: July 2007

AbstractFor four anionic impurity centers with S2‐configuration (H−, Cu−, Ag−, and Au− centers) and the F center in alkali halides, a correlation between the peak energy, E, of the absorption band concerned and the lattice constant, d is extensively investigated. All the results indicate that the Smakula (STSN) relation, E = ad−n, holds for every alkali family (a and n are adjustable parameters). The values of exponent, n, derived from the analysis for all centers treated show a systematic variation with the defect center, the absorption band, and the alkali ion. It seems that the factor n expresses a degree of the lattice relaxation. In fact, a relation between the n‐value and the Stokes‐shift ΔE concerned, is very simple. An empirical relation, ΔE = bnk, roughly holds and the constants b and k depend only on the crystal structures of the alkali halides.
ESR and Magnetic Investigation of Lithium Intercalated VSe2
Authors: Watanabe Y. 
Published: July 2007

AbstractX‐band ESR spectra are examined during the Li intercalation process of VSe2 in n‐butyllithium solution. The formation of V2+ ions at an early stage of reaction and their subsequent partial disappearance are ascertained in the case of solutions where Li contents are totally deficient for the production of Li2VSe2. The temperature‐dependence of the width of V2+ ESR lines exhibits a broad minimum around 150 K. This is interpreted in terms of effects of the interaction of V2+ ions with other vanadium ions in some different valence states.
The Simulation and Interpretation of the EPR Powder Spectra of Gd3+‐Doped LaAlO3
Authors: Koopmans H. J. A. , Perik M. M. A. , Nieuwennuijse B. , Gellings P. J. 
Published: July 2007

AbstractThe EPR powder spectra of Gd3+ doped LaAlO3 are simulated for a number of temperatures between 4 and 800 K by means of the usual spin‐Hamiltonian. Values are found for the zero field splitting parameters B(n, 0) only, which agree with single crystal measurements. For an accurate simulation of the axial powder spectra a variable linewidth has to be introduced, because an inhomogeneous broadening of the resonances in the xy plane is observed. This broadening is successfully described by a variable B(2, 2) parameter. This indicates that the Gd3+ ion does not fit within the LaAlO3 lattice, because GdAlO3 is not isostructural with LaAlO3. Crystal field calculations support this assumption.
Thermoelectric Power and Electrical Resistivity of Fe2Nb3Se15
Authors: Bansal C. , Surendranath K. 
Published: July 2007

AbstractSeebeck coefficient and resistivity of a new Fe‐substituted NbSe3 compound of stoichiometry Fe2Nb3Se15 are studied in the temperature range 77 to 300 K. It is found to show a charge density wave transition followed by a metal‐insulator transition at lower temperatures.
Conductivity of an Electron Gas in a Low‐Frequency Electric Field Due to Large‐Scale Fluctuations
Authors: Radunović J. B. 
Published: July 2007

AbstractAn expression for the conductivity of an electron gas in a low‐frequency electric field (ω < ωL) is derived. The collision integral which accounts for both, the electron‐electron (e‐e) and the electron‐phonon (e‐p) type of interactions is represented in the ν‐approximation. Furthermore, the electron gas is assumed to be a state close to equilibrium. The results are expected to be of interest for the studies of the static electron conductivity.
Structural Disorder Model of Amorphous Semiconductors: Ge and Si
Authors: Vaid B. A. , Sharma K. C. 
Published: July 2007

AbstractA structural disorder model for the amorphous semiconductors, Ge and Si, is proposed in terms of dangling bonds which are treated as point defects. Generalizing the well‐known concept of packing fraction and exploiting the strong correspondence between the crystalline and amorphous phases near the transition temperature, the contribution of dangling bonds to various thermodynamic quantities is shown to be very important. Its importance and new features are also discussed.
Theory of Compression in Ionic Crystals
Authors: Shanker J. , Narain J. , Rajauria A. K. 
Published: July 2007

AbstractA theoretical method based on interionic potentials is developed for evaluating the compression of alkali halide crystals corresponding to different values of pressure. The short range overlap repulsive interactions between first neighbours as well as between second neighbour ions are taken into account. The traditional Born method for determining the repulsive parameters is replaced by a more plausible method due to Decker. Recent values of the van der Waals dipole‐dipole and dipole‐quadrupole interaction coefficients derived from the Kirkwood‐Muller formula are used in the present calculations. Pressures are calculated corresponding to different values of compressions. The results are found to compare well with available data.
Effect of Pressure on the Raman Scattering Efficiency of GaP
Authors: Aoki K. , Cardona M. 
Published: July 2007

AbstractThe effect of pressures up to 10 GPa on the efficiencies for Raman scattering by TO and LO phonons is measured in GaP for the 1.92 and 2.18 eV laser lines. These scattering efficiencies show a logarithmic decrease with pressure. From the measured efficiencies, the lattice and electro‐optic contributions to the Raman polarizability are obtained as functions of pressure. The decrease of STO with increasing pressure is interpreted as a preresonant process induced by the increase of the E0‐gap with pressure. The second order susceptibility is also discussed on the bases of a simple dispersion model.
Charge Transfer and Energy of Formation in Binary Alloys: CsCl Intermetallic Compounds
Authors: Chakraborty S. , Manna A. , Ghosh A. K. 
Published: July 2007

AbstractThe density functional obtained through Löwdin's α‐expansion method is utilized to study equi‐volume charge transfer and energy of formation of equiatomic ordered transition intermetallic compounds having CsCl structure. Electronic charge is transferred, by and large, in the direction as expected from the Pauling electronegativity series. The computed formation energies predict the stability of compounds satisfactorily. It is concluded that the α‐expansion method may be applied with confidence to study ground state properties of metals and alloys.
Two‐Phonon Resonance Raman Scattering and Quantum Interference Effects in Polar Semiconductors in High Magnetic Fields
Authors: Belitsky V. I. , Goltsev A. V. , Lang I. G. , Pavlov S. T. 
Published: July 2007

AbstractThe EHP contribution to the two‐phonon resonance Raman scattering (RRS) cross‐section is calculated for a polar semiconductor located in a high magnetic field H. This contribution is of order α, where α is the Fröhlich electron (hole)‐LO phonon coupling constant (in the case H = 0 the cross section is of order α2). This α‐dependence results from the quasi one‐dimensional motion of the electron (hole) in a high magnetic field. For such a polar semiconductor as InSb (α ≈ 0.013 ≪ ≪ 1) a high magnetic field leads to a sharp increase of the secondary radiation intensity. The two‐phonon RRS cross section is an oscillating function of the magnetic field H and (or) of the incident light frequency ω1. The oscillations exist due to the increase of the density of states near the Landau zone bottom. It is shown that in the vicinity of a number of values of the magnetic field H = H0/L, where H0 = mecωLO/|e|, (me(e) = effective mass (charge) of electron, L = 1/2, 1, 3/2, 2, …, there is a number of additional contributions of interferential character to the cross section, which lead to a resonance decrease of the secondary emission intensity.
Effect of Magnetic Field on the F‐Band Absorption in NaCl and KCl Single Crystals Irradiated with X‐Rays under DC Fields
Authors: Chaudhary R. K. , KrishnaRao A. V. , Rao K. V. 
Published: July 2007

AbstractOptical absorption is measured in the F‐band region of NaCl and KCl single crystals X‐ray irradiated under de fields and also later subjected to a magnetic field perpendicular to the (100) faces. The presence of de fields during irradiation seems to produce an absorption band overlapping the F‐band on the long wavelength side. The magnetic field tends to resolve this band from the F‐band of these crystals. An attempt is made to understand these results.
Effect of Forced Vibrations on the Scattering of X‐Rays and Mössbauer Radiation by a Crystal (I)
Authors: Dzyublik A. Ya. 
Published: July 2007

AbstractA general scattering theory of photons (particles) by field targets, periodically depending on time is developed. On the basis of this formalism the scattering of γ‐quanta is considered by a crystal, which performs enforced vibrations under the influence of alternating fields. The Raman scattering amplitudes and corresponding cross‐sections for scattering and absorption of γ‐quanta by the crystals are calculated. The possibility of compensation of the recoil energy for γ‐resonance at energies ≈200 keV by infrared lasers is analysed.
Magnetization and Spin‐Flip Raman Scattering in Cd1−xMnxS
Authors: Nawrocki M. , Planel R. , Mollot F. , Kozielski M. J. 
Published: July 2007

AbstractHigh‐magnetic field magnetization data are reported on Cd1−xMnxS alloys, with x = 3% and 15%. Effective parameters describing the Mn—Mn interaction are deduced. Spin‐flip Raman scattering from donors provides a measure of the s—d exchange interaction.
Low‐Temperature FMR and FMAR Measurements of Metal Single Crystals. II. Saturation Magnetization, Magnetocrystalline Anisotropy, and g‐Factor Determination
Authors: Půst L. 
Published: July 2007

AbstractFMR and FMAR fields measured on Fe—3.16 wt% Si single crystals between 3.5 and 300 K at microwave frequencies between 35 and 96 GHz are used to evaluate the saturation magnetization μ0Ms, the first magnetocrystalline anisotropy constant K1, and the g‐factor temperature dependences with accuracies of ±0.5 mT, ±0.15 kJ/m3, and ±0.0004, respectively. The g‐factor is found to be temperature independent and the temperature dependence of μ0Ms is described according to the spin‐wave theory.
On the Thermoelectric Power of Amorphous Ferromagnets
Authors: Richter R. , Goedsche F. 
Published: July 2007

AbstractThe spin‐disorder model is adopted to calculate the electrical resistivity and thermoelectric power of ferromagnetic metallic galsses within the molecular field approximation. The resistivity expression interpolates correctly between the low (T = 0 K) and the high temperature (T ≧ TC) results derived previously. Using Mott's formula a magnetic contribution Sm(T) to the thermopower is calculated which exhibits a nonlinear temperature dependence. Both, sign and curvature of Sm(T) are correlated with the actual position of 2kF in the structure factor. For a combined spin and potential scattering the total thermopower is evaluated according to the Nordheim‐Gorte rule. The results reproduce qualitatively sign and curvature of the thermopower observed experimentally in ferromagnetic metallic glasses.
First‐Principles Calculation of Deformation Potentials of Copper Halides
Authors: Christensen N. E. 
Published: July 2007

AbstractSelf‐consistent, relativistic LMTO band structure calculations, using the local‐density approximation, are performed for strained CuCl and CuI crystals in the zinc‐blende structure. Equilibrium volumes and bulk moduli are derived. Calculations for uniaxially strained crystals are used to deduce deformation potentials for splitting of the Γ15‐state (top of the valence band) with and without spin—orbit coupling (SO). In case of trigonal strain, these quantities are calculated as a function of the internal‐strain parameter ζ. It is shown that the deformation potentials can be evaluated by moving the potentials obtained by one self‐consistent calculation for the unstrained crystal to the lattice positions of the strained crystal. The inclusion of SO is important in the calculation of the trigonal‐shear deformation potentials but affects only slightly those for tetragonal strain.
Visible Luminescence of Colour Centres in Sapphire
Authors: Springis M. J. , Valbis J. A. 
Published: July 2007

AbstractThe colour centres introduced in sapphire crystals by neutron irradiation and by thermochemical treatment exhibit polarized luminescence. In neutron‐irradiated crystals an absorption band at 4.1 eV and luminescence bands at 2.45 and 3.8 eV are due to one type of centres, most probably interstitial aluminium ions. Other donor‐type centres give rise to an absorption band at 2.75 eV and a luminescence band at 2.2 eV. In magnesium containing crystals similar centres absorbing at 2.93 eV and emitting at 2.35 eV can be introduced by thermochemical treatment in reducing atmosphere. The preliminary study of the red luminescence indicates its connection with the absorption bands at 3.45 and 3.8 eV.
Investigation of the Equation of State and the Grüneisen Parameters for Transition Metal Oxides
Authors: Agrawal S. K. , Narain J. , Shanker J. 
Published: July 2007

AbstractThe equations of state of the four transition metal oxides MnO, FeO, CoO, and NiO are investigated from the knowledge of interionic potentials. Recently determined values of the Van der Waals dipole—dipole and dipole—quadrupole interaction energies are used in the present paper. The repulsive interaction energies for unlike ion pairs as well as like ion pairs are taken into account upto second neighbours. Different values of repulsive hardness parameters are used for different pair interactions. The compression values corresponding upto about 250 kbar are calculated and reported. Good agreement between theoretical and experimental values is obtained. The second neighbour interactions between the oxide ions are found to be quite significant and much stronger than the interaction between transition metal ions. Values of the Grüneisen parameter and its volume derivative are also estimated for the crystals under study.
New Results on the Decay Properties of Perturbed and Unperturbed M‐Centers in NaCl:CaCl2
Authors: Bosi L. , Gagliardelli P. , Nimis M. 
Published: July 2007

AbstractLifetime measurements concerning the relaxed excited state of the perturbed and the unperturbed M‐center in X‐ray colored NaCl:CaCl2 samples, give the following results: a) the decay spectra are characterized by two components, due to the perturbed ((18.2 ± 0.5) ns at 9 K)) and to the unperturbed ((26.5 ± 0.5) ns at 9 K) M‐center respectively, in the temperature range 9 to 320 K: the component due to the perturbed M‐center disappears at higher temperatures; b) the lifetime of the M‐perturbed center is a decreasing function of the temperature contrary to what happens in KCl samples doped with divalent impurities, where it is constant up to room temperature; c) no difference from the data obtained in undoped NaCl samples is noted for the unperturbed M‐center and it is shown, for the first time, that its lifetime decreases above 310 K; d) the simple scheme of a two‐channel decay process is not valid for the perturbed M‐center whereas it enables to fit with accuracy the data concerning the unperturbed M‐center (by assuming a de‐excitation energy value equal to (0.46 ± 0.02) eV). An analysis of the optical properties of the M‐perturbed center in NaCl:CaCl2 samples leads to the assumption that the perturbative effect is low compared to that observed in KCl doped with divalent impurities: in particular, it seems to be inefficient as regards the absorption properties; this hypothesis also enables to explain the absence of formation of Z4‐centers in the same samples.
Thermal and Magnetic Properties of CrxMn1−xAs Compounds
Authors: Bärner K. , Santandrea C. , Neitzel U. , Gmelin E. 
Published: July 2007

AbstractThe specific heat of magnetically ordered metallic CrxMn1−xAs crystals is determined in the temperature range 100 K < T < 500 K for nine compositions. Several anomalies in the specific heat are observed and assigned to carrier localization effects, spin fluctuations, and long range spin ordering. For the compositions x = 0.5, 0.4, 0.2, and 0.1 a sequence of two magnetic specific heat peaks are observed and interpreted in terms of a “magnetic alloy” model.
Solitary Clusters of Spin Deviations and Lattice Deformation in an Anharmonic Ferromagnetic Chain
Authors: Pushkarov Kh. I. , Primatarowa M. T. 
Published: July 2007

AbstractAn anisotropic Heisenberg ferromagnetic chain is considered where the lattice deformation caused by the spin deviations is taken into account both, in harmonic and anharmonic approximation. The possibility of solitary bound formation between spin clusters and lattice deformation is investigated. It is shown that such a solitary “domain” can exist and propagate along the chain with constant velocity and without “smearing”. In this way a magnetic moment can be transferred without dissipation.
Polarizability Studies of Amorphous Silicon
Authors: Ravindra N. M. , Morhange J. F. , Thomas P. A. , Ance C. 
Published: July 2007

AbstractAn attempt is made to evaluate the polarizability of amorphous silicon. These evaluations are carried out for samples prepared by chemical vapour deposition (CVD) and glow‐discharge (GD). Spectroscopic models like that of Wemple‐Didomenico and Ance are employed for the purposes of calculation. This study may serve as a bridge between experimental results that follow from Raman or infra‐red spectroscopy and those that are obtained from absorptance/reflectance studies.
A Calculation of Absorption Potentials for Low Energy Electrons in MgO, 2H‐MoS2, and 2H‐NbSe2
Authors: Smith A. E. 
Published: July 2007

AbstractA simple calculation scheme for determining the absorption potential for low energy electron scattering in crystalline materials, based on experimental values of the dielectric loss function, is outlined. In particular calculations are performed for the semiconductors magnesium oxide and molybdenum disulphide together with the metal niobium diselenide. A larger value of the mean absorption potential for the metallic compound is found and its implication for low energy total current measurements is commented upon.
Resonant Energy Transfer in Ruby under Magnetic Field
Authors: Ferrari M. , Montagna M. , Gonzo L. , Viliani G. , Pilla O. , Farace G. 
Published: July 2007

AbstractThe effect of a magnetic field on the single ion‐single ion resonant transfer in ruby is investigated theoretically by using a simple model. It is found that the field induces a quenching of the resonant transfer. The results are compared with recent experimental data.
Quantum Freeze‐Out of Carriers in Semimetallic and Semiconducting Thin Wires
Authors: Arora V. K. , Spector H. N. 
Published: July 2007

AbstractA semimetal—semiconductor transition is predicted to take place due to the quantum freeze‐out of carriers in semimetallic thin wires. These wires are assumed to be cylinders of radius R0 although this quantum freeze‐out effect is also predicted to take place in thin wires of rectangular cross section as well. In cylindrical wires, the onset of semiconducting behavior is expected to occur at a critical radius R*0 = α01ħ/(2M Δ)1/2, where α01 = 2.405 is the first zero of the Bessel function of the zeroth order, M = memh/(me + mh) is the reduced mass of the electron—hole system, and Δ is the overlap of the conduction and valence bands. For wires of radii smaller than R*0, the electrical conductivity of the thin wire will exponentially decrease with temperature because of the presence of an effective band gap Eg = (αħ2/2 M R) ‐ Δ > 0.
Ultrasonic Attenuation in Quasi‐One‐Dimensional Ferroelectrics
Authors: Aksenov V. L. , Yu. Didyk A. , Plakida N. M. 
Published: July 2007

AbstractThe ultrasonic attenuation in uniaxial ferroelectrics with the stronglyanisotropic spectrum of order‐parameter fluctuations is considered. It is shown that quasi‐one‐dimensional character of fluctuations dispersion leads to qualitatively new effects in the behaviour of ultrasonic velocity and attenuation. The theory allows one to explain qualitatively recent experiments on ferroelectrics CsH2PO4.
Multiphoton Absorption in Solids Non‐Perturbative Approach in the Weak‐Field Limit
Authors: Brandi H. S. , Jalbert Ginette , Malta O. L. 
Published: July 2007

AbstractA closed analytical expression for multiphoton transition rate, in direct gap crystals, is obtained from a non‐perturbative approach in theweak‐field limit. This scheme is related to an approximate high order perturbation theory and compared with tunneling‐like theories as proposed by Keldysh. The accuracy and the limitations of the use of the saddle‐point in this type of methods are discussed.
Screening in a System of Many Particles Composed of Two Charged Fermions Application to Excitons
Authors: Stolz H. , Zimmermann R. 
Published: July 2007

AbstractA many‐particle system of composite particles consisting of two different fermions each and interacting by the Coulomb potential is considered. For the case that the composites are present in bound states only the constituent self‐energy is calculated to linear order in the densitytaking all symmetries of the many‐body wavefunctions into account. The correlational part (screening part) of the selfenergy is calculated in the Born collision approximation. Numerical values for the shift of the continuum‐edge of the spectrum of excitons in GaAs are presented.