bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamical Nature of Superexchange Interaction in Y3Fe5O12 Studied by Neutron Spectroscopy
Authors: Ligenza S. 
Published: July 2007

AbstractInelastic neutron scattering is used to investigate spin interactions in polycrystalline Y3Fe5O12. Neutron spectra due to local spin interaction are observed and interpreted by the 6S5/2‐term splitting of Fe3+ ions located in octahedral (a)‐sites and tetrahedral (d)‐sites of the garnet structure. The observed neutron spectra are analyzed using a phenomenological spin Hamiltonian assuming combined interaction of magnetic and quadrupole electric moments of the 3d5 electron shell with a static magnetic molecular field and a static electric field gradient, respectively. The neutron energy peaks connected with various magnetic coordination numbers at (a)‐sites and (d)‐sites are obtained. This phenomenon is interpreted as due to the dynamical nature of superexchange interaction of Fe3+ ions in YIG. The dynamical interactions bring about fluctuations of the magnetic moments with a relaxation rate between 10−8 s > τm > 10−13 s. The quadrupole and superexchange interaction parameters are determined to D = −0.508 meV and Es = 3.00 meV, respectively. The effect of lowering of magnetic moments of Fe3+ ions situated on (a)‐ and (d)‐sites is discussed.
Commensurate‐Incommensurate Transition in a Quasi‐One‐Dimensional Conductor with a Nearly 1/3‐Filled Band
Authors: Fischbeck H. J. , Mertsching J. 
Published: July 2007

AbstractThe commensurate‐incommensurate transition in a quasi‐one‐dimensional system with commensurability three is studied using the continuum, the mean‐field, and the one‐kink‐band approximaions. Except for special cases, the commensurate‐incommensurate transition is discontinuous in general. The lattice distortion, the chemical potential, and the spectrum of the electrons at the transition are calculated and related to known results from alternative approximations.
Electronic Structure of Perfect Chemisorbed Monolayers and of Disordered Surfaces
Authors: Beckmann A. 
Published: July 2007

AbstractOn the basis of a simple tight‐binding model, the local spectrum of a semiinfinite crystal is discussed on the surface layer of which both the local energy levels and the transfer integrals are changed with respect to the bulk. The two cases of an ordered and a substitutionally disordered surface are considered. For the transfer integrals the multiplicative type of Shiba is generally presumed. It is shown that for considerable deviation of the surface transfer integrals from those of the bulk (i) the local density of states shows a quasi two‐dimensional behaviour, and (ii) surface state bands may split into two separate parts.
Ionicity and Static Ionic Charge
Authors: Enders P. 
Published: July 2007

AbstractRecently, Falter et al. have proposed an ionicity scale basing on the longitudinal effective charge eL (that is wrongly identified with the static ionic charge q). It is shown that ionicities that vary linearly with q or eL are, however, not appropriate to construct structural maps, and it is concluded that nor q, nor eL is very relevant or even a measure for structural properties.
Measurements of Proton Channeling Energy Losses in Silicon in the Intermediate Energy Region
Authors: Gehrmann P. , Lenkeit K. , Stolle R. 
Published: July 2007

AbstractThe energy loss of protons in the energy region from 40 to 350 keV is measured for (110), (100), and (111) planar channeling, for 〈110〉, 〈111〉, 〈112〉 axial channeling, and for random directions in silicon. The investigations are carried out by means of the transmission experiment using silicon targets of several thicknesses. Stopping power values are derived from the peak and the leading edge of energy spectra for channeled particles. Special procedures are applied to correct the obtained stopping power data with respect to the target thickness. In the case of leading edge the stopping power data depend strongly on the target thickness. It is shown that only the extrapolation to zero thickness leads to correct stopping power values for best channeled particles. It is found that the ratio of channeled to random stopping power shows a maximum in the energy region at about 70 keV. Here the stopping power for channeling and random directions reach their largest value, too.
Electronic Contribution to the Ordering Energy of a Binary Alloy
Authors: Bortel K. 
Published: July 2007

AbstractThe band theory of the phase transitions in the binary alloy of transition metals is investigated by means of the Landau theory and coherent potential approximation, CPA. The investigation of the mechanisms responsible for the transition from disordered to ordered phase of an alloy is the main purpose of the considerations. It is shown that the asymmetry of interactions and energy transfer are the primary causes of the ordering process in a binary alloy.
Low Energy Electron Exchange Excitation of 4f Transitions and Location of 4f Levels in Rare Earths
Authors: Bauer E. , Kołaczkiewicz J. 
Published: July 2007

AbstractEu, Gd, and Tb single crystal films and atomically dispersed layers adsorbed on W(110) surfaces are studied by low energy electron loss spectroscopy. A very sharp dominant loss peak at about 4 eV is analyzed in detail and attributed to spin exchange excitation of the 4f level. This interpretation agrees very well with self‐consistent spin‐polarized free atom and band structure calculations. The results are compared with XPS and other experimentel data which leads to a reconsideration of the interpretation of the 4f XPS binding energies.
Bound Phonons
Authors: Balkanski M. , Jouanne M. , Kanehisa M. 
Published: July 2007

AbstractThe strong electron‐phonon coupling, occurring when the energy of the electronic excitation is comparable to that of the LO mode, is treated in two cases: (i) the electronic state is a localized impurity level and (ii) the electronic excitation is an interband transition continuum between valence or conduction bands in degenerate n‐ and p‐type silicon. In the first case the mixed bound electron‐phonon state has as many bound‐phonon levels as electronic excitation energies, deduced from detailed band structure, coming in close coincidence with the LO‐phonon energy. In the second case the electron‐phonon coupling results in frequency shifts and phonon line deformations due to phonon binding to the electronic states.
Optically Induced Nernst‐Ettinghausen Effect in the Far Infrared and Strong Magnetic Fields in HgTe and InSb
Authors: Knap W. , Stȩpniewski R. , Fantner E. 
Published: July 2007

AbstractVoltage generation in strong magnetic fields (0 to 6 T) in HgTe and n‐InSb under far‐infrared illumination is observed. The fine structure of the observed voltage versus the magnetic field is interpreted as being due to transitions between Landau sublevels. A new method of experimental determination of the nature of the observed voltage is presented. It is shown that for both the materials investigated, the observed phenomenon is due to the optically‐induced Nernst‐Etting‐ hausen effect. From the qualitative analysis it is concluded that at low temperatures and in quantisizing magnetic fields, the phonon drag is the main process responsible for the observed voltage in both, InSb and HgTe.
Light Transmission at the 1s‐Exciton Resonance of CdS in the Presence of a Density Profile of Excitons
Authors: May V. 
Published: July 2007

AbstractThe pumped transmission spectrum of a CdS platelet at the 1s‐exciton resonance is calculated for the case of high exciton densities and spatial inhomogeneous distribution of excitons. The lowering of the Is level and the increase of damping due to high excitations are considered linear in the exciton density. The corresponding wave equation for the electric field strength with spatial varying dielectric function is solved approximately. A remarkable dependence of the transmission coefficient on the density profile in the platelet is obtained.
On the Conductivity Mechanism of Weakly Doped Polyacetylene
Authors: Frankevich E. L. , Kadyrov D. I. , Sokolik I. A. , Pristupa A. I. , Kobryanskii V. M. , Zurabyan N. Y. 
Published: July 2007

AbstractThe decrease of the electrical conductivity of pristine and weakly iodine‐doped polyacetylene, (CH)x, films under the action of an external magnetic field has been revealed. The dependence of the relative decrease of the (CHx) electrical conductivity in the external dc magnetic field is typical for magnetic field spin effects with participation of pairs of paramagnetic species with spin 1/2. The magnetic electron spin resonance signal detected via the (CH)x electrical conductivity change has been revealed. The dependence of the magnetic field effect on the ac magnetic field frequency (up to 9 kHz) has been measured. A model of the observed phenomenon has been proposed based on the magnetic field effect on the probability of the charge carrier hop in pairs of paramagnetic species “polaron‐defect” in the conjugated chain.
On the Suppression of X‐Ray Anomalous Transmission by Acoustic Oscillations
Authors: Entin I. R. 
Published: July 2007

AbstractIt is shown that the Debye‐Waller factor describes correctly the Borrmann effect acoustic suppression only within the short‐wave range (λs ≪ τ, λs ultrasonic wavelength, τ extinction length). The suppression factor is expressed both, for long‐wave (λs ≫ τ) and intermediate (λs ≈ τ) cases. An analysis of the published experimental data establishes that an incorrect description of the suppression effect by the Debye‐Waller factor can cause an error of several orders when determining displacements by the measured attenenuation of anomalous transmission. In some cases experimental results demonstrate the main contribution of X‐ray acoustic resonance to be suppression effect.
Dynamic and Static Aspects in the Theory of Itinerant Spin Glasses
Authors: Kolley E. , Kolley W. 
Published: July 2007

AbstractA superfield formulation of the Langevin dynamics for itinerant‐electron spin glasses is developed. Before taking the quenched configuration average the field‐theoretical scheme involves the supersymmetry. For comparison the standard replica method combined with Bogolyubov's variational principle is used to get the statics. The spin‐glass transition temperature is calculated in the presence of spatial fluctuations as well as in the mean‐field limit.
Magnetic Properties of Amorphous Fe90.6Zr9.4
Authors: Beck W. , Kronmuller H. 
Published: July 2007

AbstractThe temperature dependence of the spontaneous magnetization, Ms, and the magnetization curve of melt‐spun amorphous Fe90.6Zr9.4 alloys are investigated by means of a SQUID magnetometer in the temperature range 4.2 K < T < 150 K, and for magnetic fields 1 mT < μ0H < 4 T. At low magnetic fields, μ0H < 80 mT, Ms is found to obey a T2 law whereas for μ0H >0.27 T Bloch's T3/2‐law is obtained. No evidence for a spin‐glass transition at low temperatures can be detected. The high‐field susceptibility points to the presence of circular quasidislocation loops.
Chemical Shifts and EXAFS of the LIII Absorption Discontinuity of Dysprosium in Some of Its Compounds
Authors: Islam M. S. 
Published: July 2007

AbstractThe LIII X‐ray absorption discontinuity of dysprosium is studied in the pure element and in some of its binary and ternary compounds. A graph of the chemical shift ΔE in binary compounds against the effective charge q on the absorbing atoms is plotted. This plot is helpful in determining the effective charges in ternary compounds in which they cannot be calculated theoretically. The EXAFS (extended X‐ray absorption fine structure) in the vicinity of discontinuities is also recorded and interpreted with the help of the graphical method given by Lytle et al.
Green Function, Local Density of States, and Statistical Equilibrium in Muffin‐Tin Systems
Authors: Lenk R. , Solbrig H. 
Published: July 2007

AbstractFor a muffin‐tin potential a multiple scattering problem where all scatterers act only aS black‐box entities is separated in general form from those relations which yield the wave field within a, given muffin‐tin sphere. This separation renders possible the construction of the Green function. In comparison with other formulations the role of the fields incident at the individual scatterers is emphasized. In a second step the close connection is employed between the Green function and the density matrix in a statistical equilibrium state. This yields an explicit and exact formula for the statistical mean values of all intensity‐like quantities which are bilinear in the angular momentum projections of the incident fields. Reciprocity properties are treated, too.
Optical Switching Behaviour in Two‐Beam Experiments with CuCl
Authors: Levy R. , Bigot J. Y. , Frindi M. , Hönerlage B. 
Published: July 2007

AbstractAn investigation is made of the transmission properties of a test beam through CuCl samples and through Fabry‐Perot etalons containing CuCl under simultaneous excitation of a pump beam. For appropriately chosen photon energies of the two beams, the transmission of the test beam through the sample decreases due to nonlinear absorption, or increases when the sample is in a F.P. resonator. The switching behaviour indicates that the nonlinear absorption and dispersion properties of CuCl depend on the exciton and biexciton population dynamics.
Optical Absorption Studies on Colored KCl:Na:Pb Crystals
Authors: Dalal M. L. , Sivaraman S. , Murti V. Y. G. S. 
Published: July 2007

AbstractThe nature of the Pb‐centers in colored KCI:Na:Pb crystals is studied by optical absorption spectroscopy. The crystals are colored by exposure to X‐rays and y‐rays as well as by electolysis and nonstoichiometry. A large number of absorption bands are observed most of which are attributed to either the Pb centers or the Pb° centers.
Study of the Sensitization Effect of Eu2+ Ions on the Trivalent Rare‐Earth Fluorescence in CdF2 Crystals
Authors: Jouart J. P. , Bissieux C. , Mary G. , Egée M. 
Published: July 2007

AbstractIt is shown that, under visible or near infrared excitation, the Eu2+ ion sensitizes the [RE3+, F] fluorescence in as‐grown and annealed CdF2 crystals (RE  Sm, Eu, Er) cooled at 77 K and previously irradiated with UV light. Non‐radiative energy transfer from Eu2+ in cubic surroundings to minor [RE3+, F] complexes, via the conduction band of the host lattice, is identified. The sensitization mechanism is based on the photoionization of Eu2+ ions and requires the simultaeous presence of neutral interstitial fluoride ions (F), each associated with a RE3+ ion. This study demonstrates the existence of three kinds of interstitial fluoride ions in CdF2. From the excitation spectrum of the RE3+ fluorescence, a value (1.1 eV) is deduced for the photoionization threshold of Eu2+ ions in CdF2, close to the theoretical value obtained from the Pedrini et al. model. Besides, the Eu3+ fluorescence spectroscopy is used to determine the symmetry of the site occupied by Eu2+.
On the pressure dependence of grüneisen parameter in solids
Authors: Kumari M. , Dass N. 
Published: July 2007

AbstractA simple theory is developed to study the pressure dependence of Grüneisen parameter, γ. The final results show that γ varies linearly with the pressure, that is, γ(p, T) = γ(0, T) – ηp where η is found to be a pressure‐independent but temperature‐dependent parameter. Moreover, it is shown that η is related to some other thermodynamic parameters and hence can have positive or negative magnitude which in turn will decide whether γ(p, T) decreases or increases with pressure. The calculated values of γ(p, T) in the whole range of pressure and temperature are found in very good agreement with the experimental results in case of all the solids studied like NaCl, CaF2, MgO, quartz, Na, K, and Li. Further, it is shown that the second Grüneisen parameter, q, and the Debye temperature, θ, can also be calculated as a function of pressure with the help of the present theory.
Electron potential energy near the ferromagnetic metal– vacuum interface
Authors: Gabovich A. M. , Voitenko A. I. 
Published: July 2007

AbstractThe charge electrostatic energy W(z) near the surface of a metal with an arbitrary spontaneous magnetization 0 ≦ ζ ≦ 1 is calculated using the random‐phase approximation for the metal dielectric function. It is shown that the variation of the surface value W(0) under the ferromagnetic transition amounts up to 12% of its original value and depends on free‐electron concentration. Such a variation can be observed in LEED experiments.
Density functional pseudopotential calculation of the cohesive properties of Ordered (CsCl‐Type) compounds of nontransition metals
Authors: González D. J. 
Published: July 2007

AbstractThe density functional formalism is used to calculate the electron density, equilibrium volume, and heat of formation of ordered (CsCl‐type) alloys of nontransition metals. A cellular method is employed to separate the alloy in atomic cells with appropriate matching conditions at the cell boundaries. The ion cores are substituted by empty core pseudopotentials. The results are compared with other theoretical results and with the experiment.
Time‐resolved luminescence of CdGaInS4 under pulsed laser excitation at 30 K
Authors: Colocci M. , Fermi F. , Querzoli R. , Vinattieri A. 
Published: July 2007

AbstractA detailed study of the time‐resolved luminescence of CdGaInS4, after pulsed laser excitation at T = 30 K is presented. Results are given on the time‐resolved spectra in the range 50 ns to 10 ms of delay time with respect to excitation, on the time decay of the luminescence intensity at 610 nm, and on the time evolution of the integrated luminescence intensity for different emission wavelengths. Finally a simple model is presented for the recombination processes at low temperatures yielding good agreement with the experimental data.
Spectial features of lattice dynamics and electron‐phonon interaction in Re
Authors: Shitikov Yu. L. , Tulina N. A. , Zemlyanov M. G. 
Published: July 2007

AbstractThe dynamic properties of the rhenium lattice are investigated using the methods of neutron and point‐contact spectroscopy. Based on the double differential cross‐sections of inelastic neutron scattering measured at 300 and 500 K the phonon spectra of rhenium are reconstructed with regard to the coherence effects. From the results of measurements of the second derivative of the current–voltage characteristic made in various Re point‐contact, a mean point‐contact function of electron‐phonon interaction is obtained. The features of electron–phonon interaction function coincide within the experimental error with those of Re phonon spectrum on one and the same energy interval. Thus, the phonon spectrum participates entirely in the formation of the electron–phonon interaction function.
Thermal expansion coefficients of ternary AIIIBV solid solutions
Authors: Pietsch U. 
Published: July 2007

AbstractAs experimentally established recently the atoms of a particular sublattice of ternary AIIIBV solid solutions are elongated out systematically of their regular positions. Using a Keating like approach for the strain energy of the relevant binary compounds the thermal expansion coefficient of some ternary solid solutions are calculated by means of a perturbation treatment relative to the values which are interpolated linearly between these ones of binary end components. The calculated bowing parameters coincide with the experimental findings published till now.
Theoretical analysis of the chemical activivity of noble gas atoms in silicon
Authors: Gagarin S. G. , Mudryi A. V. , Pushkarchuk A. L. , Ulyashin A. G. , Teterin Yu. A. 
Published: July 2007

AbstractThe possibility of formation of a chemical bond between noble gas atoms (Ne, Ar), ion‐implanted into silicon, and matrix atoms is treated theoretically in a cluster representation using both, the scattered‐wave Xα (SW‐Xα) and complete, neglect of differential overlap (CNDO/2) electronic structure methods. It is shown that the presence of noble gas atoms in the silicon lattice results in formation of inner valence molecular orbitals (MO) when Ar and Ne atoms interact with Si atoms. A theoretical analysis is made of the results of possible investigations of these structures by photo‐electron spectroscopy measurements.
Electron states in periodic dislocation networks in semiconductors
Authors: Nabutovskii V. M. , Romanov D. A. 
Published: July 2007

AbstractThe misfit dislocation electron propagation is studied as an example of quantum particle behavior in a periodic network. Transitions in the net sites are described by the S‐matrix formalism. The energy band structure for a rectangular network cell is investigated. Particularly, the analytical form of the dispersion law is obtained in the quadratic cell case. It is shown that the incommensurability of lattice periods leads to an intrinsic stochasticity of the electron spectrum. Anomalies of conductivity, galvanomagnetic, and high‐frequency properties as functions of band occupation and applied electric and magnetic fields are discussed.
EPR of Nd3+ ions in Y‐type zeolites
Authors: Trif Eleonora , Nicula Al. 
Published: July 2007

AbstractAn analysis is made of the EPR spectrum of Nd3+ ions entered by ion exchange (1%) in Y‐type zeolite. The hydrated samples show an isotropic EPR signal at geff ≈︁ 2.73. This resonance arises from ions located in sites of C3 symmetry. The experimental EPR signal is identified with the theoretical isotropic EPR transitions at g = 2.62. The isotropy of the EPR signal advocates the pathology of the zeolite crystals, i.e. the absence of the complete long‐range order in Y‐type zeolites.
Fractional moments. New source of information in radiospectroscopy
Authors: Nigmatullin R. R. 
Published: July 2007

AbstractA new fractional moments method for the absorption and dispersion curves in radiospectroscopy is suggested. The fractional moments solve the problem of moments existing in the mathematical statistics and enable one to restore the complex susceptibility ξ(ω) and the relaxation function Φ(t) completely. The bond between the fractional moments of the ξ(ω) and the function Φ(t) is found. The possible applications of this method for experimental measurements are shown.
Conductivity tensor of a two‐dimensional electron gas in a strong magnetic field in higher orders of perturbation theory. Quantum hall effect
Authors: Balev O. G. , Boiko I. I. 
Published: July 2007

AbstractThe components of the conductivity tensor σ are considered for the case of a strong magnetic field H. The investigation of the higher orders in perturbation theory up to the fourth order in static scattering potential shows that for an electric field E under the condition E ≪ E0  [heH3/2m2c3]1/2 the Hall conductivity magnified image and the transverse conductivity σyy ∼ exp (−E/E2here Ne, is the carrier concentration. In virtue of the extreme small collisional contribution to the conductivity the picture of the quantum Hall effect is similar to that for an ideal noninteracting two‐dimensional electron gas.
Off‐diagonal conductivity and magnetization of PdFe, PdCo, and PdNi alloys in coherent potential approximation calculated on the basis of realistic models of component densities of states
Authors: Voloshinskii A. N. , Ryzhanova N. V. , Vishnekov L. Yu. , Obukhov A. G. 
Published: July 2007

AbstractThe concentration dependence of the off‐diagonal component of the electroconductivity tensor and that of the average magnetic moment are calculated for PdFe, PdCo, and PdNi alloys in the coherent potential approximation (CPA). These calculations are based on realistic models of the component densities of states (DOS's). Experimental and theoretical results are compared.