bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of Localized Magnetic Moments in FeCrAl Alloys and the Electron Structure
Authors: Blau W. , Mager S. , Wieser E. 
Published: July 2007

AbstractThe localized magnetic moments of Fe and Cr are determined by combination of saturation magnetization measurements and magnetic diffuse scattering. Power series characterizing the interactions between the different kinds of atoms in the alloys are chosen to describe the concentration dependence of the magnetic moments. The different terms are discussed on the basis of band structure models valid for dilute alloys taking into account their modification by impurity interactions.
Magnetooptical Investigation of Hg1−xCdxTe Mixed Crystals. I. Semimetallic Configuration
Authors: Guldner Y. , Rigaux C. , Mycielski A. , Couder Y. 
Published: July 2007

AbstractSubmillimeter resonance spectroscopy and interband magneto‐absorption are applied to the investigation of the Hg1−xCdx Te alloys system in the range of composition x < 0.3. Magneto‐transmission measurements are performed at 4.2 K up to 60 kG in both the spectral regions (ħω < 16 meV and ħω > 120 meV), on identical unoriented samples, in the Faraday and Voigt geometries. Magnetooptical data are analyzed using the virtual crystal approximation. All interband and intraband magnetooptical transitions are interpreted in terms of Γ6 and Γ8 Landau levels described by the Pidgeon and Brown model. The Kane matrix element, the interaction gap, and the Luttinger parameters are determined for each alloy composition from the comparison between theory and experiments. Magnetooptics also provide information on the evolution of the resonant acceptor states with the composition.
Vibrational and Electronic Structure of Hydrogen‐Related Defects in Silicon Calculated by the Extended Hückel Theory
Authors: Singh Vijay A. , Weigel C. , Corbett J. W. , Roth L. M. 
Published: July 2007

AbstractExtended Hückel theory calculations are carried out for interstitial hydrogen atoms in silicon model crystals without and with vacancies. The energetically stable positions for the hydrogens appear to be the tetrahedral interstitial site in crystals without vacancies; in the case of vacancies the hydrogens favor positions in the dangling bonds of the vacancies 0.35 bond lengths away from the vacancy nearest neighbors. The vibrational frequencies for all defect types considered are in very close agreement with infrared bands observed after proton irradiation of silicon. The frequencies increase with the number of hydrogens in a vacancy. The hydrogen‐related impurity levels are very close to the valence band edge, both above or below.
Positron Annihihtion in Colour Centres
Authors: Nagarajan T. , Ramasamy P. , Ramasamy S. 
Published: July 2007

AbstractThe angular correlation of positron annihilation in NaCl and KCl is compared for various concentrations of F‐centres produced by γ‐irradiation as well as additive doping. The intensity and the “full width at half‐maximum (FWHM)“ ‐Γ1/2 of the narrow component are slightly different for each of the X‐irradiated, electron‐irradiated, γ‐irradiated (light and heavy doses), and addi‐tively doped crystals. The possible role of additional defect centres in trapping positrons is discussed. Also angular correlation measurements of positrons annihilating in the reversible F ⇌ F' conversion centres in equilibrium in additively coloured KCI at −100 °C are given.
On the Theory of Additional Light Waves and Boundary Conditions in Anisotropic Crystals
Authors: Pekar S. I. 
Published: July 2007

AbstractIt is shown that the exciton contribution to the crystal polarization is not quite correctly separated in some papers. Therefore the additional boundary conditions derived there as well as formulas for the reflection coefficients are correct only if the waves in the crystal are strictly transversal. A general method is developed of separating the exciton contribution to the polarization for arbitrary angles between the wave vector and the electric field strength. The case of uniaxial crystals is considered in detail for the frequency region containing two near exciton transitions, both of them contributing to the dispersion. In this case the incident monochromatic ray generates in the crystal two ordinary rays and three nonordinary rays. The boundary conditions are derived for these rays. An expression is obtained for the light reflection coefficient of the crystal.
On Magnon‐Acoustic Phonon Interaction in Magnetic Semiconductors
Authors: Balkarei Yu. I. , Nikitov V. A. 
Published: July 2007

AbstractThe electronic mechanism of spin‐acoustic phonon interaction is investigated in a wide band ferromagnetic semiconductor with high concentration of charge carriers at temperatures when the magnon system is highly excited. The dispersion equation for longitudinal acoustic phonons is obtained and is studied in the region of their interaction with the spectrum of the magnon branch. It is shown that the dimensionless constant of magnon‐acoustic phonon coupling in degenerate semiconductors can be larger than the ordinary magnetoelastic interaction constant and is very close to it in non‐ degenerate ones. A principal possibility to single out experimentally the electronic part in the spin‐acoustic phonon coupling constant is discussed.
The Application of CPA to Calculations of the Mean Magnetic Moment in the Gd1‐x‐,Nix, Gd1‐x ‐,Fex, Gd1‐x ‐,Cox, and Y1‐x ‐,Cox Intermetallic Compounds
Authors: Szpunar B. , Kozarzewski K. 
Published: July 2007

AbstractCalculations are made of the mean magnetic moment per atom of the transition metal and the rare‐earth metal in the intermetallic compounds, Gd1‐x,Nix, Gd1‐x Fex, Gd1‐x Cox, and Y1‐x Cox. A simple model of the disordered alloy consisting of spins localized on the rare‐earth atoms and interacting with a narrow d‐band is considered. The magnetic moment of the alloy at zero temperature is calculated within the molecular field and Hartree‐Fock approximations. Disorder is treated in the coherent potential approximation. Results are in good agreement with the experimental data obtained for the crystalline and amorphous intermetallic compounds.
Transformations of the Hubbard Model
Authors: Mertsching J. 
Published: July 2007

AbstractThe significance of some transformations of the Hubbard model with an arbitrarily occupied symmetric band in a magnetic field is studied. The repulsion‐attraction transformation yields nontrivial relations between solutions of the Hubbard model with a positive and a negative correlation energy, respectively. As an example, the connection between an antiferromagnet in a magnetic field and a superconductor with a non‐half‐filled band is discussed.
The Derivation of a Direct Formula for the Hall Coefficient
Authors: Schiller W. , Röke G. , Buhr G. , Christoph V. 
Published: July 2007

AbstractA direct formula for the Hall coefficient is derived by using the non‐equilibrium statistical operator formalism of Zubarev‐McLennan. The formula for the Hall coefficient expressed by correlation functions is discussed in the weak scattering limit, and the equivalence to the Kubo expression for the Hall coefficient is shown.
Many‐Body Effects on the Fourth‐Order Elastic Constants of Ionic Solids
Authors: Garg V.K. , Puri D. S. , Verma M. P. 
Published: July 2007

AbstractExpressions for the fourth‐order elastic (FOE) constants are derived from the Lundqvist potential for ionic solids along the line adopted in the derivation of the expression for the second‐order elastic (SOE) and third‐order elastic (TOE) constants. As in the case of the SOE and the TOE constants it is observed that the Cauchy relations among the FOE constants are broken even at O K and discrepancies in these relations are directly expressible as functions of the many‐body term in the crystal potential. The expressions for the FOE constants suggest that they must satisfy four identities so that the number of independent constants is only seven. It is suggested that measurements of fourth‐order elastic constants at O K in conjunction with these identities can provide an useful test for the validity of the Lundqvist potential in ionic solids.
Subnanosecond Time‐Resolved Spectroscopy of the Biexciton Luminescence in CuCl
Authors: Ostertag E. , Grun J. B. 
Published: July 2007

AbstractThe biexciton luminescence of CuCl at 4.2 K is studied under intense UV picosecond excitation, and its time dependence is investigated in the range of 0 to 800 ps by means of an ultrafast optical sampling gate. The time‐resolved spectra of the luminescence due to the radiative recombination of biexcitons show a change in shape of this emission band during the first 100 ps, which may be due to the relaxation time of the biexcitons by means of acoustical phonons. A dynamical model, taking into account the collisions between biexcitons and excitons, is proposed, which provides an acceptable fit for the time dependence of the luminescence if a value TM= 1 ns of the spontaneous radiative decay time of the biexcitons is assumed.
Phenomenological “Dilution Model” for Kondo‐Type Effects in Concentrated Alloy Systems
Authors: Yao Y. D. , Arajs S. , Anderson E. E. 
Published: July 2007

AbstractPossible phenomenological treatments of Kondo‐like behavior in non‐dilute metallic systems are described. The approach is a “dilution” treatment of non‐dilute alloys in which moment clusters are considered as approximate single impurity magnetic moments. Possible consequences of this phenomenological approach are briefly discussed.
Determination of Tb2Ni17, Er2Ni17, and Tm2Ni17 Magnetic Structure by Neutron Diffraction
Authors: Yakinthos J. K. 
Published: July 2007

AbstractNeutron diffraction measurements on the intermetallic compounds Tb2Ni17, Er2Ni17, and Tm2Ni17 show that these materials are ferrimagnet,ic below their Curie temperatures 178, 166, and 152 K, respectively. This magnetic property is in agreement with previous susceptibility data. Tb2Ni17 and Er2Ni17 have collinear magnetic structure with magnetic moments which are perpendicular and parallel to the c‐axis of the crystals. Tm2Ni17 has a canted magnetic structure. The coupling between rare earth and nickel moments is negative, whereas the coupling between atoms of the same kind is positive. The measured mean value of the rare earth moment in the above compounds is 8.6, 8.0, and 6.0μB. respectively. The nickel moment is 0.3μB. Bertaut's macroscopic theory gives magnetic modes compatible with the magnetic structure experimentally observed. Crystal field calculations give two different anisotropy directions for the two rare earth sites.
Semi‐Empirical Pseudopotential Calculation for the Electronic Structure of Polymeric Sulfur Nitride
Authors: Chelikowsky J. R. , Schlüter M. , Cohen M. L. 
Published: July 2007

AbstractA three‐dimensional band structure calculation is performed for polymeric sulfur nitride. Using the semi‐empirical pseudopotential method, we calculate the electronic density of states with and without pressure, the optical spectrum, the valence charge density, and the Fermi surface. The bonding properties of (SN)x are explored via an analysis of the valence charge density as a function of energy and by means of an angular momentum projection of the electronic density of states. The shape of the Fermi surface is investigated. Estimates for the electron‐phonon coupling constant, λ, are given, and the increase of Tc with pressure is discussed.
Effect of the Next‐Nearest Neighbour Coupling in a Semi‐Infinite Ferrimagnet
Authors: Diep‐The‐Hung  
Published: July 2007

AbstractThe surface spin‐wave energy in a semi‐infinite Heisenberg ferrimagnet is calculated. The study is based on a body‐centered‐cubic structure with a (100) surface as the outermost layer and where the exchange interactions between nearest‐neighbours,J1and between next‐nearest neighbours,J2, are taken into account. The conditions under which the uniform spin configuration becomes unstable are derived by considering a surface “soft” mode. Surface spin rearrangement is also discussed.
Plasma Oscillations in a Superlattice
Authors: Shmelev G. M. , Ciiaikovskii I. A. , Pavlovich V. V. 
Published: July 2007

AbstractTho spectrum of plasma oscillations, propagating along the superlattice (SL) axis is calculated in the random phase approximation (RPA) taking the umklapp processes into account. In the case of strong screening the plasmon frequency is determined by SL parameters and temperature and found to do not depend on wave number. At weak screening quasineutral electron oscillations occur. In the case of small wave numbers the oscillations follow the acoustic law of dispersion and propagate with a frequency of the same order as the electronic ones along the SL axis. The characteristic feature of plasmons propagating along the SL axis, is the absence of Landau damping since the decay of these plasmons in pairs of quasi‐particles is forbidden by energy‐momentum conservation laws. The existence of plasmons, propagating along the axis, may be an indication of electron tunnelling between layers.
Kinetics of Dilute Solid Paramagnets under “Bottleneck” Conditions
Authors: Grinberg E. S. , Nicmatullin R. R. 
Published: July 2007

AbstractKinetic equations, describing a dilute paramagnet in “bottleneck” (BN) conditions, are obtained in the case of spin‐lattice mechanism of longitudinal and transverse relaxation of electron spins (direct processes). The spectral distribution function of phonons, obtained in stationary conditions, is compared with the corresponding function for a concentrated paramagnet. The influence of the resonance phonons on the spin‐system is considered. The possibility of studying the phonon avalanche in dilute paramagnets by pulse techniques is mentioned.
Multiple Scattering of Electrons by an Infinite Lattice Plane II. On the Properties of the Planar Scattering Matri
Authors: Solbrig H. 
Published: July 2007

AbstractThe symmetry properties of both the angular momentum representation and the plane wave representation of the planar scattering matrix are derived and discussed. The generalized optical theorem is obtained from the current balance of the muffin‐tin layer. For the case without absorbing medium the absorption matrix of the muffin‐tin layer is calculated in terms of the partial absorption cross sections of the muffin‐tins.
Optical Properties of Cu and Ag in the Intermediate Region between Pure Drude and Interband Absorption
Authors: Hollstein T. , Kreibig U. , Leis F. 
Published: July 2007

AbstractThe complex dielectric constant ϵ of thick Cu and Ag films on fused quartz substrates is determined at 300 and 1.5 K by a modified v. Fragstein‐Kampermann method in the spectral region between 0.41 and 0.71 m̈n. The relaxation frequency of the conduction electrons is determined and the contributions of electron‐phonon, electron‐surface, electron‐lattice, and electron‐electron scattering are separated. No further absorption mechanisms have to he taken into consideration to explain the experimental results. By decomposing ϵ into interband and conduction electron contributions, the temperature dependence of the interband transition edge of Cu is evaluated. The edge is shifted from 2.18 eV (1.5 K) to 2.15 eV (300 K). There are indications of indirect transitions, but a quantitative determination is not possible.
A New Group‐Theoretical Approach to Cell‐Preserving Phase Transitions in Crystals
Authors: Aoyei A. K. , Birman J. L. 
Published: July 2007

AbstractIn a previous paper the crystal space group representations associated with cell‐preserving phase transitions and the independence of sublattice transitions were investigated. Based on that paper, a simple method for determining the space group and microscopic structure of the daughter crystal arising in any such transition is developed. In the process a new, “site” subduction criterion is derived, which is more restrictive than the Birman subduction criterion. The theory is applied to the structural transition that occurs in the A‐15 compounds. The daughter‐crystal space group of V3Si and Nb3Sn is found to be C74V. This group and the predicted microscopic daughter‐crystal structure are consistent with the available experimental data.
Influence of a DC Field on the Free Polaron Infrared Absorptio
Authors: Huybrechts W. J. 
Published: July 2007

AbstractThe optical absorption by polarons in weakly polar semiconductors is studied in the presence of an external dc field as function of temperature. The LO‐phonon field is treated by perturbation theory. Firstly, a comparison is made between the absorption curves obtained for different orientations of the dc field with respect to the polarization vector of the infrared radiation, and secondly, the temperature‐dependent approximation is compared with the well‐known Gurevich‐Lang‐Firsov perturbational result calculated for zero external electric field.
Exchange Energy of a Strongly Inhomogeneous Electron Gas
Authors: El‐Mamoun E. , Ropke G. 
Published: July 2007

AbstractThe problem of exchange energy of a strong inhomogeneous electron gas is treated within a special model. An explicite expression for the density of exchange energy is given in dependence on the electron density as well as the gradient of the electron density, where the electron density and its gradient independently can take any arbitrary value. As a result, the relative difference between this expression and the local density approximation for the exchange energy strongly depend on the fractional change in the electron density over the local Fermi wavelength. The deformation of the Fermi‐hole in a strong inhomogeneous electron gas is considered.
Theory of Absorption and Dispersion Profiles of Molecular Transitions in Dense Media
Authors: Paeeschke H. , Süsse K.‐E. , Welsch D.‐G. , Wilhelmi B. 
Published: July 2007

AbstractStarting from quantum theoretical principles the phase relaxation is described of a molecule localized in a dense medium by an integro‐differential equation. Using this equation, which leads to a non‐exponential phase decay, general formulas are derived for calculating the absorption and dispersion profiles of vibronic and vibrational transitions of the guest molecule. In detail the calculations are performed for the case that the acoustic phonons of the medium are responsible for the phase relaxation. Especially it is shown, that in comparison with the Lorentz profile the wings of a real absorption profile become steeper with increasing ratio between dephasing rate y and Debye frequency wD‐ Only for γ/wD ≪ 1 the absorption profiles are expected to be Lorentz profiles. The dispersion is found to increase with increasing ratio γ/wD. Both the real absorption and dispersion curves are asymmetric ones.
Theory of Surf‐Riding Electrons on the Wake Potential of Ion Beams in a Metal
Authors: Suzuki K. , Ohtsuki Y. H. , Kitagawa M. 
Published: July 2007

AbstractThe surface plasmon excitation and the quantum‐mechanical effect are taken into account in the surf‐riding electrons on the wake with ion beams in the metal. It is concluded that the surface plasmon excitations play an important role when the glancing angle of the incident ion beams to the crystal surface becomes smaller. The binding energy levels and the angular distribution of the surf‐riding electrons are calculated in detail.
Formation Energy of Spherical Cavities in Metals
Authors: Gyémánt I. , Solt G. 
Published: July 2007

AbstractThe formation energy of a spherical cavity in a metal is calculated by means of the density functional formalism, with gradient expansion for the kinetic energy. The method adds to earlier work by studying the energy as a function of the cavity radius S at a given density of the metal. Further, combining the statistical formalism with a pseudopotential description of an embedded ion, the heat of solving one (like or unlike) atom in the metal is also obtained. Despite the crude simplifications in the method, i.e. the statistical treatment of the density functional problem and the inherent limitations of the jellium model on the one hand, and the low flexibility of the simple trial density function on the other hand, the cavity formation energies and the trends in the energies of solution are realistic in the majority of cases.
Effect of Pressure on the Spectrum of Praseodymium‐Doped Single Crystals
Authors: Voloshin V. A. , Krimnus M. G. 
Published: July 2007

AbstractThe absorption spectrum of praseodymium‐doped single crystals at 78 K and P = 22 kbar is analyzed. It is found that the shift of the LSJ levels under pressure is due to the change of the electrostatic interaction of 4f electrons.
A Pseudopotential Approach to the Electronic Theory of Short‐Range Order
Authors: Khvaya F. A. , Katsnelson A. A. , Silonov V. M. , Khrushchov M. M. 
Published: July 2007

AbstractExpressions for the local ordering energy and short‐range order parameter of the substitional solid solution with components having different valencies are obtained by using the pseudopotential method in second order perturbation theory. The calculations give a satisfactory agreement with experiment for the Al‐Zn system.
Adsorption of oxygen at room temperature on polycrystalline titanium studied by ultraviolet and X‐ray photoelectron spectroscopy
Authors: Hagsteöm A. L. , Platau A. , Kaelsson S.‐E. 
Published: July 2007

AbstractTitanium films, freshly evaporated and exposed to varying amounts of oxygen, are studied by ultraviolet and X‐ray photoelectron spectroscopy (UPS and ESCA), using HeI, HeII and AlKα1,2 radiation. The valence band results are compared with previous experimental results and with reported densities of states. Contrary to previous results, no pronounced decrease in the emission from Ti 3d states is observed in the 21.2 eV spectrum at exposures of ≦ 3 × 10−4 Torr s. Information about the reaction kinetics is extracted from ESCA measurements. The intensity of the O Is photoelectron line is found to increase with exposure according to a logarithmic relation below about 10−6 Torr s and to saturate above about 10−4 Torr s. In the saturated region recordings of the Ti 2p doublet revealed presence of a TiO2 layer with a thickness of one to two monolayers.Titanschichten, die unmittelbar nach dem Aufdampfen unterschiedlicher Sauerstoffexponierung ausgesetzt waren, werden mit Hilfe von Ultraviolett‐ und Röntgen‐Photoelektronenspektroskopie (UPS und ESCA) untersucht. Dabei wird HeI, HeII‐ und AlKα1,2‐Strahlung angewendet. Die Ergebnisse, die für das Valenzband erhalten werden, werden mit früheren experimentellen Ergebnissen und mit Zustandsdichten aus der Literafcur verglichen. Im Gegensatz zu früheren Ergebnissen wird keine deutliche Abnahme der Emission aus Ti 3d‐Zustanden im 21,2 eV‐Spek‐trum bei Exponierungen ≦ 3 × 10−4 Torr s beobachtet. Aus den ESCA‐Messungen können Informationen über die Reaktionskinetik gewonnen werden. Die Intensität der O Is‐Photoelektronen‐Linie steigt bei Exponierung unter ca. 10−5 Torr s gemäß einer logarithmischen Beziehung und geht oberhalb von ca. 10−4 Torr s in eine Sättigung über. Im Sättigungsgebiet zeigt das Auftreten des Ti 2p‐Dubletts, daß eine TiO2‐Schicht mit einer Dicke von ein bis zwei Monoschichten vor‐handen ist.
Temperature and hydrostatic pressure dependence of vibrational modes in PbTi1–xZrxO3
Authors: Bäuerle D. , Holzapfel W. B. , Pinczuk A. , Yacoby Y. 
Published: July 2007

AbstractThe room temperature Raman spectra of PbTi0.1Zr0.9O3 at hydrostatic pressures up to 68.5 kbar indicate three phase transitions. At 5.71 kbar a new phase appears, most probably the rhombo‐hedral high‐temperature phase, FR(HT) which is in coexistence with the rhombohedral low‐temperature phase FR(HT). Between 8 and 9.1 kbar the relative intensities of all lines change and two additional structures appear. It is likely that this change is due to a transition into the orthorhombic antiferroelectric phase. A further transition between 39.7 and 42 kbar cannot be positively interpreted on the basis of the present data. The temperature dependence of the Raman spectra gives evidence that the additional structure in the FR(LT) phase is due to the doubling of the unit cell, i.e. PbTi1–xZrxO3 seems to show one‐mode behaviour.