bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic Properties of Dysprosium Oxisulphate (Dy2O2SO4)
Authors: Hülsing H. , Kasten A. 
Published: July 2007

AbstractBelow TN = (8.05 ± 0.10) K Dy2O2SO4 is a nearly two‐dimensional co‐linear Ising antiferromagnet. At low temperatures (T ≦ 2.4 K) and in external magnetic fields between 1.7 and 2.2 T along the ordering direction there is an intermediate ferrimagnetic phase with a T = 0 magnetization of 1/3 of the saturation value. From Zeeman spectroscopy and theoretical considerations the structure of the magnetic phases are derived. The details of the phase diagram as established by magnetization measurements are not reproduced by mean field calculations. At the boundary between the antiferromagnetic and ferrimagnetic phase there is a hysteresis which is asymmetric with respect to the sweep direction of the external magnetic field. This behaviour can be explained by the occurrence of different magnetization processes. The time constants as determined experimentally are of the order of ten minutes.
A Raman Study of Compositional Disorder in Defect Chalcopyrites
Authors: Razzetti C. , Lottici P. P. , Zanotti L. , Curti M. 
Published: July 2007

AbstractThe growth and Raman scattering results obtained for ZnGa2xIn2(1−x)S4, ZnxCd1−xGa2S4, and CdGa2xIn2(1−x)S4 tetragonal pseudoternary compounds are given and discussed. The phonon spectra display one‐ and two‐mode behaviour. For ZnxCd1−xGa2S4 compounds a virtual crystal model seems to describe the observed one‐mode behaviour.
Spin‐one lattice gas model for isotherm‐reversal in spin‐labelled lipid monolayers
Authors: Chakraborty K. G. , Baret J. F. 
Published: July 2007

AbstractA suitably extended version of a spin‐one lattice gas model, embodying the basic ideas of Cadenhead and Müller‐Landau and Bell and Dunne, is employed to study the “isotherm reversal” appearing in the pressure—area phase diagram of spin‐labelled monolayers. Considering the nine different configurations of molecules as concieved by Bell and Dunne the Hamiltonian is developed and the molecular field approximation is applied to derive the expression for pressure. The phase diagrams are drawn for various values of the model parameters and it is seen that the isothermreversal is a characteristic of the model itself. Unlike the one‐dimensional model of Bell and Dunne, the present model shows the phase transition from a liquid‐expanded to a liquid‐condensed phase.
Calculation of the properties and the structure of ordering alloys of the Cu—Au system
Authors: Kolodeznaya S. F. , Kozlov E. V. 
Published: July 2007

AbstractBy using the method of OPW‐pseudopotential (OPW‐PP) the ordering energy of copper—gold alloys, the short‐range and long‐range order structures, and the transition temperature are calculated. In many parameters the calculated values are in good agreement with the experimental ones. The level of approximation and the ways of the further development of the theory are discussed.
Towards a molecular theory of the solid—liquid phase boundary. Elementary kinetic processes
Authors: Klupsch Th. 
Published: July 2007

AbstractStarting from the molecular, structural theory of the f.c.c. crystal—liquid phase boundary for onecomponent Lennard‐Jones systems near the triple point given by the author, the elementary kinetic processes of particles undergoing solid—liquid transitions are studied, and the absolute transition time is determined which is about 10−10 s. Starting with calculations of the mean square of the fluctuating force for extremely inhomogeneous systems such as the interface, and calculations of a space‐dependent friction coefficient via generalizations of the Mori formalism, the investigations are based on a description of the stochastic single‐particle motion by means of the Smoluchowski equation. It is shown that the stochastic single‐particle motion is closely related to the cell dynamics of stochastic lattice models; the corresponding absolute transition probabilities are calculated.
New arguments to the problem of screening in auger recombination in semiconductors
Authors: Ziep O. , Mocker M. 
Published: July 2007

AbstractThe band‐to‐band recombination rate of Auger recombination is derived by means of correlation functions of non‐equilibrium systems. In distinction to previous work where unscreened exchange interaction or static dielectric functions enter the corresponding matrix elements, the Coulomb as well as the exchange term of the Auger scattering amplitude is described by wave‐vector and frequency‐dependent dielectric functions. The results are compared qualitatively with existing calculations of Auger recombination.
A pseudopotential approach to the lattice parameters for GaAs containing impurity elements
Authors: Ito T. 
Published: July 2007

AbstractA simple numerical calculation, which is applicable to estimate the impurity effects of tetrahedral compounds containing various kinds of impurity, is performed by using a pseudopotential perturbation treatment based on a simplified Heine‐Abarenkov model potential. The author proposes a new calculation method to determine potential parameters for the component elements of III–V compound semiconductors. Calculated values of total crystal energy and bulk modulus are in good agreement with the previously reported experimental data. A calculation application to GaAs lattice parameter changes caused by group VI elements (S, Se, Te) is successfully achieved.
Thermopower and thermomagnetic effects in kane semiconductors under conditions of electron and phonon heating and their mutual drag
Authors: Gasymov T. M. , Katanov A. A. , Babaev M. M. 
Published: July 2007

AbstractThe thermopower and the transverse Nernst‐Ettingshausen (NE) effect of degenerate semiconductors with Kane electron spectrum are considered taking account of electron and phonon heating and their mutual drag. It is established that in absence of a mutual drag and phonon heating the electron part of the thermopower Ve as well as the NE voltage U grow sharply on raising the external electric field strength ˜ E4 while the phonon part of the thermopower Vp does not depend upon E. It is shown that the phonon heating leads to a growth of the phonon parts Vp and Up with E: Vp ˜ E2 and Up ˜ E6. The nonparabolicity of the electron spectrum results in the growth of the phonon parts and the decrease of the electron parts of the thermopower and NE voltage if the phonons are nonheated. Mutual drag leads to a higher growth of all the above‐mentioned effects on raising the mutual drag degree γ0 if the electrons and phonons are heated. In the parabolic case under the conditions of a strong mutual drag (γ0 → 1) Up = 0. If the electrons are scattered by piezoacoustic phonons in a weak magnetic field the electron part of the NE coefficient Qe firstly decreases with growing γ0 (being positive), reaches zero at γ0 = 2/9, and then reverses its sign and grows in magnitude. A similar situation takes place in a strong magnetic field also, the only difference is that Qe = 0 at γ0 = 2/5.
Self‐heating of dense exciton Gas in CdTe single crystals
Authors: Baltramiejūnas R. , Kuokštis E. , Žukauskas A. 
Published: July 2007

AbstractHeating of the dense exciton gas is observed in highly photoexcited CdTe single crystals radiating mainly due to the exciton‐exciton collisions at the lattice temperature T = 77 K. The effective exciton temperature turned out to be an increasing function of the excitation density while the heating is independent of the exciting quantum energy. A model of exciton selfheating due to the binding and radiative recombination processes under strong interparticle interaction is proposed for the explanation of the experimental data.
Elastic fields of dislocations piercing the interface of an anisotropic bicrystal
Authors: Belov A. Y. , Chamrov V. A. , Indenbom V. L. , Lothe J. 
Published: July 2007

AbstractThe elastic field of a dislocation piercing the interface of an anisotropic bicrystal is obtained for the general case of a dislocation line refracted at the interface. The theory is based on the method of dislocation‐line force fans which reduce the three‐dimensional elastic field of the dislocation in the bicrystal to the superposition of two‐dimensional fields of straight dislocations and line forces in an infinite homogeneous medium. The suggested method should be suitable for numerical calculations of the elastic fields of dislocations in arbitrary bicrystals.
Low temperature thermal conductivity of amorphous (Fe, Ni, Co) (P, B, Si) alloys and their change by heat treatment
Authors: Pompe G. , Gaafar M. , Büttner P. , Francke Th. 
Published: July 2007

AbstractThe thermal conductivity of amorphous metallic alloys (Fe, Ni, Co)1—x (B, P, Si)x is measured in the temperature range 2 to 100 K in the as‐produced and heat‐treated states. By taking into account the results of Matey and Anderson the influence of the nature of the metalloid and the number of metallic components can be discussed. The change of the thermal conductivity due to a structural relaxation caused by a heat treatment is very different. In the whole range of temperature a rise of the phonon thermal conductivity of the Fe—Co—B alloy is obtained, whereas no change is observed for the Fe—B alloy. At low temperature (< 40 K) the thermal conductivity of the Fe—Ni—P—B alloy increases by heat treatment, whereas at higher temperatures a reduction is observed. Additionally the thermal conductivity of the recrystallized alloy Fe80B20 is investigated.
Effect of valence band splitting on the biexciton binding energy in wurtzite‐type semiconductors
Authors: Flohrer J. , Porsch M. 
Published: July 2007

AbstractA lower bound for the biexciton binding energy in wurtzite‐type semiconductors is calculated using a 64 × 64 matrix Hamiltonian obtained by the k · p method which takes into account the interband coupling‐induced nonparabolicity of the two upper valence bands A and B as well as their different anisotropies and symmetries. A properly symmetric variational ansatz for the ground state vector of the Γ1 biexciton (with AB and BB biexciton states admixed) yields an analytic expression for the binding energy. Its numerical evaluation for CdS as a function of the nonparabolicity parameters U and W shows a sensitive dependence on U, but only a weak dependence on W. It turns out that a strong valence band coupling (U = – 2h2/2m0 as proposed earlier) would result in a marked increase of biexciton binding energy due to the strong nonparabolicity of the A valence band in this case.
Changes in the electron wave phases at the exit surface of a scattering crystal located near the reflection position
Authors: Maksimov S. K. , Borgardt N. I. 
Published: July 2007

AbstractThe regularities in the changes of the electron wave phases at the exit of a scattering crystal are studied within the framework of the two‐wave dynamical theory for the Laue case with foil thickness and excitation error varying. The dynamical effects are shown to lead to a non‐linear phase change of the transmitted and diffracted waves. The results obtained are used to explain experimental defocused micrographs of a wedge‐shaped crystal with nanometer steps on its surface.
Texture analysis by iteration. I. General solution of the fundamental problem
Authors: Imhof J. 
Published: July 2007

AbstractA summary is given of the texture analysis from the elements to the solution of its fundamental problem. The crystal symmetry of the orientation and the unreduced pole‐figure is examined. The division of the orientation space is determined from the division of the pole‐figures and vice versa. The general relation for reproduction of the orientation distribution function from pole‐figure data is obtained with the help of probability theory. The applicability of the approximative formulae is analysed.
Annealing behavior of hydrogenated amorphous silicon—nitrogen alloy films prepared by sputtering
Authors: Morimoto A. , Oozora S. , Kumeda M. , Shimizu T. 
Published: July 2007

AbstractElectron spin resonance and infrared absorption measurements are performed for hydrogenated amorphous silicon—nitrogen alloy films prepared by reactive sputtering. Annealing experiments reveal the relation between paramagnetic defects and H incorporation scheme. The Si—H bond with a nearest‐neighbor N atom is found to be more heat resistant than that without a nearest‐neighbor N atom. As a result, the increment in the content of dangling bonds due to H effusion by annealing for N rich film is smaller than that for Si rich film.
A Neutron Scattering Study of Phonons in Per‐Deuterated S‐Triazine
Authors: Dove M. T. , Heilmann I. U. , Kjems J. K. , Kurittu J. , Pawley G. S. 
Published: July 2007

AbstractThe lattice dynamics of a fully‐deuterated single crystal of s‐triazine is investigated using the technique of coherent inelastic neutron scattering. Detailed measurements of the temperature dependence of the dispersion of the soft acoustic mode associated with the ferroelastic phase transition are reported and compared with the qualitative behaviour of other acoustic modes. The results are in agreement with an analysis of the acoustic dynamical matrix for this material which predicts that in the high‐temperature phase the combination of elastic constants C2eff = 1/2(C11 − C12) C44 − C214 should become unstable on cooling towards the transition temperature. This effective elastic constant is found to have a temperature dependence of the form Ceff = C0(T − T0) with C0 = 3.404 × 106 Nm−2K−1 and T0 = 172.4 K. Measurements of some optic mode frequencies are also reported.
Optical Quenching of Photoconductivity in a‐Si: H Films
Authors: Fuhs W. , Welsch H. M. , Booth D. C. 
Published: July 2007

AbstractThermal and optical quenching of photoconductivity are studied in undoped a‐Si: H‐films prepared by glow discharge decomposition of silane and rf‐sputtering. It is suggested that the quenching effects arise from thermal and optical excitation of trapped minority carriers (holes) and that the amount of quenching is controlled by the density of dangling bonds, which act as recombination centers. In the glow discharge deposited films one type of quenching centers is found which is attributed to states in the valence band tail. The thermal activation energy amounts to Et ≈ 0.3 eV whereas the cut‐off‐energy in the optical quenching spectra is considerably higher, E0 ≈ 0.65 eV. In sputtered films a second deeper set of hole traps exists possibly due to impurity contamination with energies Et ≈ 0.6 eV and E0 ≈ 0.9 eV.
Self‐Consistent Kink Lattice in a Quasi‐One‐Dimensional Peierls‐Fröhlich System with a Nearly One‐Third‐Filled Band. I. Analytical Solution
Authors: Fischbeck H. J. 
Published: July 2007

AbstractThe continuum limit of the one‐dimensional Fröhlich model with a nearly one‐third‐filled band is solved in the mean‐field approximation. The gap function connected with the static lattice distortion exhibits a periodic array of amplitude‐modulated 2π/3 phase kinks which gives rise to the formation of a band of electronic states within the Peierls gap of the trimerized phase. The selfconsistent gap function and the electronic energy spectrum are analytically calculated.
Texture Analysis by Iteration. II. Special Cases of the General Solution
Authors: Imhof J. 
Published: July 2007

AbstractThree special solutions of the general system of equations in part I are examined with the help of an accurate model function. It is concluded that the parameters of the general solutions are of importance in the case of finite pole‐figure data. An unfavourable effect of the conditional ghost correction method suggested by Matthies and Vinel is shown.
An Analytical Theory of FMR in Bulk Metals (Parallel Configuration). I. Dispersion Relations
Authors: Fraitová D. 
Published: July 2007

AbstractA linear solution of Maxwell's equation for the propagation of electromagnetic waves in a ferromagnetic metal in the region of ferromagnetic resonance is presented; the motion of the magnetization vector is described by the Landau‐Lifshits equation (including the exchange effect in the damping term). Dispersion relations (DR) are derived for the roots of the bicubic secular equation, representing three waves of generally combined electromagnetic‐spin‐wave character. They are compared with the DR for the case of low‐conductivity ferromagnets; the crossover effect is discussed.
Dielectric Relaxation at the Glass Transition as a Free Volume Process. A Single Relaxation Time Approach
Authors: Alegria A. , Barandiarán J. M. , Colmenero J. 
Published: July 2007

AbstractFree volume theories describing structural relaxation in glasses are applied to the α‐dielectric relaxation occurring around Tg (the glass transition). Only a single relaxation time, τ, which represents the main contribution to the experimentally observed distributions, is considered. The influence of the thermal story is discussed. The unrealistic experimental values of the activation energy and preexponential factor found in the glassy zone are explained in this framework as also are the compensation laws associated with the glass transition. Measurements of τ in the range 10−8 to 104 s are performed in PVC and PAr, showing good agreement with the used model.
The Temperature Dependence of the Conductivity near the Localization Threshold
Authors: Zvyagin I. P. 
Published: July 2007

AbstractIt is shown that in the region of weakly localized states the conduction in both three and two‐dimensional systems may be due to non‐optimal hopping. The regime of non‐optimal hopping is characterized by a smaller hopping distance and energy compared to the conventional variable range hopping problem. The temperature dependence of the conductivity in this regime is discussed.
Order‐Disorder Phase Transition in TEA+(TCNQ)2‐
Authors: Brau A. , Farges J. P. , Filhol A. , Grassi H. 
Published: July 2007

AbstractThe results of measurements of cell parameters by X‐ray diffraction and of differential scanning calorimetry, versus temperature, on TEA · TCNQ2are presented and compared to the σ1de conductivity behaviour. The differential scanning calorimetry measurements show a first order phase transition at 220 K attributed to the TEA disorder. From the thermal expansion a dispersion is observed of the cell parameterafor temperatures below 220 K, attributed to a certain amount of cation “ordering” at low temperatures. The variation of the cell parameterc(the direction of the TCNQ chains), versus temperature, permits the calculation of the contribution of the TCNQ columns to the total heat capacity of the TEA · TCNQ2by a simple linear model of coupled oscillators. It is found to be dominated by intramolecular vibrational TCNQ modes and by the cation movements. The chain axis component of the Debye temperature and of the Grüneisen coefficient are θc≈ 150 K and γc≈ 7.5.
Dynamic Behaviour of the s‐d Model
Authors: Wesselinowa Julia M. 
Published: July 2007

AbstractA Green function technique is developed to study the excitations and the damping of the excitations of the s‐d interaction model below Tc. The spectrum of the magnetic excitations is obtained, which consists of an acoustic and of an optical spin‐wave branch. The E+ mode is overdamped near Curie point Tc, while it is nearly undamped at low temperatures. The electronic damping is also discussed. Some numerical calculations of various effects are given, using parameters appropriate to the ferromagnetic chalcogenide spinels (such as CdCr2S4).
The Interpretation of Broadened Gd3+ EPR Spectra of Polycrystalline Ceramics
Authors: Koopmans H. J. A. , Perik M. M. A. , Nieuwenhuijse B. , Gellings P. J. 
Published: July 2007

AbstractAn interpretation is given of the broadened EPR spectra of Gd3+ ions, which are frequently observed in polycrystalline ceramics and glasses. A reasonable simulation of the spectra is obtained, when these are regarded as a superposition of a large number of normal EPR powder spectra, each of which can be described with the usual spin‐Hamitonian. These originate from the many different surroundings of the Gd3+ ions in these compounds due to the structural disorder. The result is, that only those transitions, which are independent of the zero field splitting parameters in the spin Hamiltonian, remain visible in the derivative spectrum. The interpretation is supported by the EPR powder spectrum of the Gd3+ doped compound CaHf4O9, which changes from broadened into clearly resolved, when the compound is ordered by an annealing process.
A Model for Inhomogeneous Mixed‐Valence f‐Semiconductors
Authors: De Menezes O. L. T. , Troper A. 
Published: July 2007

AbstractA simple model for an Anderson lattice, to describe inhomogeneous mixed valence f‐semiconducting compounds, is studied. The virtual excitation of 4f‐electrons to 5d‐states is an important mechanism responsible for the effective interaction between 4f‐rare earth sites. This interaction is connected to an unusual self‐energy term associated to the f‐f Green function. Considering electron‐phonon interaction in the periodic Anderson model, it is possible to describe either first order or second order semiconductor‐metal phase transitions, under increasing applied pressure. Valence changes are to be expected associated with the displayed transition.
Higher Harmonics Generated by Mobile Carriers in Semiconductors
Authors: Stramska Hanna 
Published: July 2007

AbstractA theory describing the nonlinear current density in the de external magnetic fields H in semiconductors is proposed. The addition of an energy relaxation time to the Boltzmann equation provides an analytical expression for the magneto‐conductivity in a high ac electric field. It is shown that the third harmonic in the current density is not critically dependent on the dependence of the momentum relaxation time on carrier energy, thus for r = 0 (where index r describes the type of the scattering mechanism) the conductivity has the warm form σ = σ0(1 + β(ω) E.
Comment on the Identification of Z Centres in LiF:Mg and LiF:Mg, Ti Single Crystals
Authors: Watterich A. , Földvári I. , Corradi G. , Opyrchal H. 
Published: July 2007

AbstractThe Z‐centre hypothesis in LiF:Mg and LiF:Mg, Ti systems is re‐investigated. On the basis of available optical absorption measurements, summarizing the already emerged contradictions of this hypothesis, and by comparing the characteristic properties of the Z centres in LiF with those in other alkali halides it is established that the Z centre identifications in LiF can not be considered as proved.
Photo‐Chemical Reaction Studies in Selenium‐Doped Potassium Iodide
Authors: Prakash J. 
Published: July 2007

AbstractThe absorption bands due to an isolated Se2−—anion vacancy dipole in KI lie in the near ultraviolet range. Irradiation in the short wavelength absorption bands at 243 K is found to be responsible for photo‐chemical reactions (PCR). During PCR, an impurity—vacancy dipole is destroyed with the simultaneous formation of an F‐centre. No PCR is observed when the system is irradiated at LNT. Irradiation in the long wavelength absorption bands is found to be ineffective in producing PCR.
Magnetostatic Waves in a Coaxial Cylindrical Magnetic Domain
Authors: Sigal M. A. 
Published: July 2007

AbstractThe magnetostatic problem of a coaxial cylindrical magnetic domain (CMD) (two coaxial oppositely magnetized cylinders) is solved. A disintegrated set of equations which describe separately surface and volume modes in a CMD and the matrix is derived. The characteristic equations determining the eigenfrequencies of the magnetostatic modes are obtained. It is shown that the uniform mode in CMD is a surface one and its eigenfrequency depends on the ratio of the cylinder radii, whereas the uniform mode in the matrix is a degenerate volume mode with the corresponding frequency ωa ‐ γHa.