bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature Dependence and Critical Behaviour of the Resistivity Anisotropy in Ferromagnetic Metals
Authors: Ky Vudinh 
Published: July 2007

AbstractThe resistivity anisotropy in ferromagnetic metals due to spin—orbit interaction is considered with spin correlation taken into account. The obtained temperature dependence of Δρ shows a round peak in accord with experiment. In the critical region d(Δρ)/dt diverges as (—t)1—(α + φ) (t = (T — TC)/TC, magnetic field h = 0), where φ is the cross‐over exponent.
Electronic Structure of Fe3Si‐Type Alloys I. X‐Ray Spectra of Mn3Si, Fe3Si, and Fe3Al and Comparison with Band Structure Calculations
Authors: Himsel A. , Blau W. , Merz G. , Niederlag W. , Querin U. , Weisbach J. , Kleinstück K. 
Published: July 2007

AbstractAl‐ and Si Kβx emission spectra as well as Mn‐ and Fe L2,3 emission and self‐absorption spectra of the alloys are measured using a primary Bragg‐Soller spectrometer. Within error limits, the energetical positions of features in the spectra agree with those from calculated band structures. It follows that the APW method is applicable also to magnetic alloys if the band model of ferromagnetism is used. In non‐SCF calculations the transition metal configuration 3dn‐14s1 gives better results than 3dn‐24s2, as it is concluded from the relative position of s‐ and d‐bands.
Piezo Hall Effect in p‐Germanium
Authors: Gorbachuk N. T. , Mitin V. V. , Tkhorik Yu. A. , Shvarts Yu. M. 
Published: July 2007

AbstractThe piezo Hall effect is investigated on p‐Ge samples of low (ρ300 K = 0.02 Ωcm) and high (ρ300 K = 16 Ωcm) resistivity in the temperature range 77 to 300 K for the case of current i and uniaxial stress x being parallel to the 〈100〉 and 〈111〉 crystal axes. Taking into account the dispersion law anisotropy for light and heavy holes allows to explain the experimental temperature dependence of the piezoresistivity coefficients for samples of low and high resistivity and orientational dependence of this effect. The deformation potential constants b and d are obtained which vary in the range b = — (2.2 to 2.6) eV, d = — (4.4 to 5.1) eV depending on the values of the band parameters A, B, and C given in literature. These values of b, d are considerably different from those obtained by means of the same experimental data, but without taking into account the dispersion law anisotropy.
A Test of Convergence of the Expansion of the Screening Charge Density for Impurity Ions in Semiconductors
Authors: Mohammad S. Noor 
Published: July 2007

AbstractIn the development of the theory of potential of an impurity ion in semiconductors the Fermi‐Dirac integral F1/2 appearing in the density of the screening charge ϱ(r), is expanded in powers of the potential. In the solution of the Poisson equation with ϱ(r) always the problem arises about how many terms in the expansion of F1/2 one should account for to get a meaningful result. It depends on the convergence of the series. A critical study is made of the convergence of the series. For this new formulae for the Fermi‐Dirac integral are proposed, and it is observed that the said convergence is more pronounced for the degenerate sample than for the non‐degenerate one.
Room Temperature Investigation of the Photostimulated Afterglow in KCl:Eu2+ Crystals
Authors: Vassilev Y. , Karamikhailova M. , Mladenova M. , Georgiev M. 
Published: July 2007

AbstractKCl:Eu2+, γ‐irradiated at room temperature, is known to luminesce on photoexcitation in the F band with the emission spectrum of the impurity ion. Several experiments are made now: firstly, the emission—excitation spectrum is found to exhibit a peak at about 600 nm. Secondly, the samples are excited with the SH of a mode‐locked Nd glass laser. The maximum emission response occurs delayed at about 400 ns relative to the laser‐pulse peak. The luminescent quantum yield is estimated to be about 1%. The decay kinetics of the phosphorescent tail is also followed. A tentative model is discussed in which the luminescence results from a two‐step electron tunneling between excited F and Eu levels.
Peculiar Properties of Surface Magnetism in Thin Film Alloys
Authors: Zagórski A. , Nazarewicz W. , Ferchmin A. R. , Sukiennicki A. 
Published: July 2007

AbstractConcentration and exchange dependent Curie temperature is discussed within the framework of the Ising model as a function of film thickness. Phase diagrams include a magnetic phase induced by the surfaces which is most likely to appear in surface‐enriched films at the percolation threshold.
Dielectric Behaviour of Non‐Crystalline Model Systems Employment of an Embedding‐Field Method
Authors: Lenk R. , Ziegenhals G. 
Published: July 2007

AbstractFor a disordered system composed of identic spherically symmetric multipoles the relationships between averaged local and corresponding macroscopic field quantities are explored for static electric fields. This dielectric problem its analogous to the problem of multiple scattering of waves in a disordered muffin‐tin system. Therefore it is treated by an adaption of an embeddingfield method formerly developed for multiple scattering. The two different versions of the embedding scheme both yield the well‐known Lorentz formula for the local electric field. On the other hand, different results are obtained for the derivative of the field.
Magnetic Interactions in α‐MnSeO4, α‐FeSO4, and β‐FeSO4
Authors: Wegener W. , Hautecler S. , Legrand E. , Will G. 
Published: July 2007

AbstractThe energy distributions of neutrons scattered by α‐MnSeO4, α‐FeSO4, and β‐FeSO4 in their paramagnetic state are measured by means of a time‐of‐flight technique. The values of two exchange parameters can be estimated from a simultaneous analysis of the second moment of these energy distributions and of the Néel temperature computed in the Green's function approximation. Various two‐parameter analyses are performed and checked by comparing calculated and experimental values for θ and χ(TN). For α‐FeSO4 the dominant interactions occur between the first and second neighbours. For β‐FeSO4 two‐parameter analyses do not lead to a satisfactory description of all data; however, one can conclude that the interactions between third neighbours are important, in agreement with the stability conditions for the observed spin configuration.
Impact Ionization and Magneto‐Transport in InSb in High Crossed Electric and Magnetic Fields
Authors: Ašmontas S. , Dargys A. , Subačius L. 
Published: July 2007

AbstractHigh‐field microwave conductivity and impact ionization due to hot carriers are studied experimentally in n‐ and p‐type InSb at liquid nitrogen temperature in magnetic fields B up to 2.3 T. The employment of high microwave fields instead of dc electric fields allowed to overcome the problem of an uncontrollable breakdown caused by the Hall field at the precontact regions in high‐mobility semiconductors. It is found that the threshold field of impact ionization ET increases with B in n‐type as well as in p‐type InSb. In n‐InSb at high magnetic fields (μB » 2π) the ratio ET/B is found to be constant and close to that calculated recently by Bruhns and Hübner. From the measurements of microwave conductivity in prebreakdown fields it is possible to deduce an electron Hall drift velocity vy. It is found that vy is a function of the ratio E/B only, although due to the hot electron effects a systematic deviation of vy from the simple relation vy = E/B is observed.
First‐Order Raman Scattering in NiS2—xSex
Authors: Lemos V. , Gualberto G. M. , Salzberg J. B. , Cerdeira F. 
Published: July 2007

AbstractThe Raman spectra of the system NiS2—xSex are investigated for x = 0.00, 0.10, 0.20, 0.30, and 0.55, at room temperature and at temperatures below the point where the x = 0.55 sample suffers a resistivity change from semiconducting (T ≥ 120 K) to metallic (T ≥ 120 K). No qualitative or anomalous quantitative changes in the spectrum of the sample are found that could be associated with the anomaly in its transport properties. A mode of Ag symmetry appears in the alloys which is absent from the spectrum of pure NiS2. This mode is successfully explained in terms of vibrations of S—Se pairs. Other modes decrease in frequency with increasing selenium concentration, a trend easily understood considering the increase in the unit cell volume with increasing x.
Compositional Dependences of Critical Point Phonons in Mixed Zincblende Crystals
Authors: Jahne E. , Ulrici B. 
Published: July 2007

AbstractThe compositional dependences of long‐ and short‐wavelength critical point phonons in mixed zincblende semiconductors are studied within the framework of an interpolation scheme between the end‐member compound phonons which is founded by an “averaged Green's function” technique. The derived dependences on composition agree with those expected from a model with three virtual atoms per unit‐cell (pseudo‐unit cell model). Explicit results are presented for the compositional dependences of the Γ, X, and L point phonons in In1−xGaxP and Gap1−xAsx and compared with experimentally derived phonon frequencies.
Experimental and Theoretical Investigations on the Picosecond Deactivation Process of Excited F‐Centres in KCl
Authors: Schubebt M. , Vogler K. 
Published: July 2007

AbstractThe deactivation behaviour of optically excited F‐centres in KCl is investigated for the first time by picosecond laser spectroscopy. It is found, that a certain portion of them returns to the ground state during 20 to 150 ps. This fast deactivation process, which depends on the F‐center concentration and the coloration method, can be explained by a model based on energy transfer between excited F‐centres, whereby an inhomogeneous spatial distribution can be taken into account. The critical transfer distance is observed to be R0 = (106 ± 15) Å. Quantitative characteristic results about the inhomogeneous spatial distribution of the F‐centres are presented.
Optical Nuclear Polarization in the 1:1 CT‐Crystal Anthracene/Tetracyanobenzene. Consequences of the Phase Transition at 206 K
Authors: Auch W. , von Schütz J. U. 
Published: July 2007

AbstractIn the 1:1 CT‐complex anthracene/tetracyanobenzene the optical excitation of triplet states causes a nuclear polarization (ONP), which is two orders of magnitude larger than the Boltzmann magnetization. In single crystals this ONP is investigated as a function of the temperature (1.6 K ≦ ≦ T ≦ 300 K), of the magnetic field (0 < Bp ≦ I T) and of the angle between Bp, and the molecular axes. From the extrema of the ONP curves the identity and orientation of the triplet state inducing the ONP may be determined. In addition from cross‐relaxation experiments a quadrupole coupling constant A = (1.0 ± 0.1) MHz and an asymmetry factor η = 0.08 ± 0.02 for the 14N nuclei of TCNB is found. Below the phase transition temperature at Te = ± 206 K the anthracene molecules occupy two magnetically inequivalent positions. For the ONP process between 205 and 40 K this magnetic inequivalence is released by the delocalisation of the triplet state as an exciton.
The Linear Transverse Ising Model with Four‐Spin Interactions
Authors: Morgan M. J. 
Published: July 2007

AbstractA systematic approximant expansion due to Suzuki is applied to a simple quantum spin system; namely the linear transverse Ising model with four‐spin interactions (lattice coupling) described by the Hamiltonian . The free energy per spin and specific heat of this quantum model is calculated for the first three approximants to the partition function, and the results are discussed within the framework of the findings of other authors.
Temperature Dependence of Raman Scattering and Partial Disorder in AgI Crystals
Authors: Mariotto G. , Fontana A. , Cazzanelli E. , Fontana M. P. 
Published: July 2007

AbstractA detailed study is made of vibrational dynamics in silver iodide by the temperature dependence of Raman scattering from liquid helium temperature up to melting. A complete set of data like temperature dependence of intensity of all features, of the degree of polarization of the spectra, of peak position and halfwidth clarifies the complex nature of dynamics of β‐AgI. It is shown that the anomalous features of Raman spectra are very likely due to the one‐phonon density of states connected with the onset of partial disorder in the β‐phase. In α‐phase an anomalous decrease of Raman cross section is found with increasing temperature: this effect is connected with the possibility of a continuous partial order‐disorder transition at ≈︁ 430 °C.
Investigation of the Electronic Structure of Uranium Compounds UX2 (X Pnigogen) and UAsY (Y Chalcogen) by Positron Annihilation
Authors: Dȩbowska E. , Rozenfeld B. 
Published: July 2007

AbstractThe electron momentum density distributions ϱ(p) in USb2, UP2, and UAsS are calculated for various sets of lattice harmonics Fϱ, using Mijnarends's method. The selection of the adequate set of harmonics is made by a comparison of the anisotropic parts of ϱ(p) with “difference” momentum density distributions ϱr(p) obtained on the basis of the difference angular correlation of positron annihilation quanta curves. From “summed up” distributions ϱs(p) = ϱpoly(p)+ ϱr(p) Fermi momenta along different directions are estimated. The character of the Fermi momenta changes suggests an ellipsoidal shape of Fermi surface, which corresponds to extremely large anisotropy of electric conductivity along [001] and [100] directions of the tetragonal unit cell of these compounds.
Electrical Conductivity of Ammonium Bromide
Authors: Taylor B. E. , Laskar A. L. 
Published: July 2007

AbstractThe electrical conductivity of NH4 Br single crystals is measured by both ac and dc techniques over the temperature range 50 to 130 °C. The dc conductivity as a function of temperature in both, pure and Cd2+ doped NH4Br samples shows excellent Arrhenius behavior. The activation enthalpy for conduction is 1.14 eV. Ac measurements exhibit a pronounced frequency dependent plateau at lower temperatures (≈ 50 to 100 °C). This plateau is believed to be due to a “proton loss”. Due to the existence of the plateau that masks any extrinsic region, the dc technique is more useful in the study of ionic defects in NH4Br. Assuming that transport is due to a vacancy mechanism, the enthalpy of vacancy migration is estimated to be 0.55 eV. The polarity of the vacancy is not uniquely determined.
Single‐Site Theory of Wannier Excitons in Disordered Semiconductors 11. Numerical Results
Authors: Fischbeck H. J. , Strehlow R. 
Published: July 2007

AbstractThe VKE model for semiconducting alloys (mixed crystals) and the point scatterer model with both, a discrete and a continuous distribution of impurity levels as a model for heavily doped and glassy semiconductors, respectively, are considered in a simple parabolic two‐band structure which can be direct and indirect as well. It allows to handle analytically the 𝓀 space integrals occurring in the expression for the dielectric function, which is given in the first part of this paper. In dependence of various parameters 1s exciton lines are calculated in these models mainly in a direct band structure. In the VKE model also indirect bands are studied.
Chemical Bonding, Internal Surfaces, and the Topology of Non‐Crystalline Solids
Authors: Phillips J. C. 
Published: July 2007

AbstractThe rarity of glass‐forming materials requires the existence of topologically specific principles (over and above the randomness implied by the absence of long‐range order) which optimize the glass‐forming tendency (gft). For covalent glassy semiconductors an algebraic condition predicts correctly the composition dependence of the gft. Quite generally substantial medium‐range order associated with quasi‐regular internal surfaces can be found in glasses at distances as large as 1000 Å in suitably selected thin films.
Nonstationary States of Inhomogeneously Heated Charge Carriers
Authors: Bonch‐Bruevich V. L. 
Published: July 2007

AbstractThe behaviour of the charge carriers heated in homogeneously by an intraband light absorption is studied in a hydrodynamical approximation. Conditions are stated under which a stable electron temperature superlattice exists as well as the conditions under which there are no stable stationary states; the electron liquid then moves stochastically, its temperature and velocity being bounded and randomly time‐dependent.
Conductance et magnétorésistance transversale á partir de I'équation de Boltzmann quantique
Authors: Charbonneau M. , Van Vliet K. M. 
Published: July 2007

AbstractNous discutons une équation de Boltzmann quantique obtenue récemment. Cette équation est valable pour les cas où la nature quantique du transport est d'une importance fondamentale. Comme première application, nous étudions la conductivité électrique contrölée par la diffusion sur des impuretés. Les résultats sont en accord avec ceux de Chester et Thellung et de Verboven. En deuxième lieu, nous étudions la magnétorésistance transversale dans des champs magnétiques fort et extrëmement fort, Ià où I'équation de Boltzmann elassique est complètement inadeptée. Dans le cas de la diffusion sur des impuretés, on retrouve la formule de Adams e t Holstein qui a été obtenue par une méthode d'opérateur densité ou par la théorie de Kubo. Pour le cas des collisions binaires, Line extension du résultat de Adams et Holstein a été obtenue.
On Energy‐Wave Number Characteristics F(q) in Metals as Derived from Experimental Phonon Spectra
Authors: Brosens F. , Derveese J. T. , Cornelis J. , Nihoul J. 
Published: July 2007

AbstractA method to determine the energy‐wave number characteristic of metals directly from experimental phonon spectra is discussed with respect to the uniqueness problem, and in connection with the hypothesis of a central interatomie potential.
Luminescence from an Electron‐Hole Liquid in the Indirect Compound Ga(As1−xPx)
Authors: Wilke I. , Schwabe R. , Bindemann R. , Jacobs K. , Seifert W. 
Published: July 2007

AbstractThe radiative recombination from an electron‐hole liquid (EHL) is investigated in highly excited pure Ga(As1−xPx) with indirect band structure. The experimental results reveal an arsenic‐induced radiative no‐phonon (NP) transition from the liquid phase. The comparison of the experimental and calculated lineshape of the EHL luminescence band provides the fundamental parameters of the EHL obtained for a sample with x = 0.88. The equilibrium carrier density and the work function at T = 2 K are determined to be neq = 9 × 1018 cm−3 and Φ = (20 ± 1) me V, respectively. The influence of the arsenic atoms on the energetic properties of the EHL is qualitatively discussed.
On the Influence of a δ‐Correlated Random Field upon the Interband Optical Absorption
Authors: Mironov A. G. 
Published: July 2007

AbstractThe frequency dependence of the light absorption coefficient is calculated in the tail region for disordered semiconductors with the Gaussian Δ‐correlated random field. The optimal fluctuation method is employed. The frequency dependence of the absorption coefficient reproduces the density of states energy dependence (up to some coefficients in the exponent).
Lattice Dynamics of Crystals with Off‐Centre‐Type Impurities
Authors: Plakida N. M. , Ivanov V. V. 
Published: July 2007

AbstractA model of a defect crystal with substitutional impurities in the potentials with several off‐centre minima is considered. Employing the self‐consistent phonon theory some necessary conditions for the off‐centre displacements of impurities are obtained and the resonant mode frequency is calculated. The importance of impurity fluctuations at the “local phase transition” is stressed. The theoretical results are compared with experiments in defect systems as KBr:Li+.
The Contribution of Reciprocal Lattice Vectors to Processes of Phonon‐Phonon Interaction and Lattice Thermal Conductivity
Authors: Segal A. 
Published: July 2007

AbstractOn the basis of a reformulation of the known wave vector conservation law in interaction processes with three phonons, the Boltzmann equation is solved and an equation of the lattice thermal conductivity is obtained. In this equation the average value of reciprocal lattice vectors occurs, which contribute to the three phonon interaction processes. An application of the equation obtained for different substances would offer information regarding the reciprocal lattice vectors which contribute to these processes.
ENDOR Study of Atomic Hydrogen on Cation Sites in KCl Doped with Sr++
Authors: Studzinski P. , Niklas J. R. , Spaeth J. M. 
Published: July 2007

AbstractAtomic hydrogen trapped on cation sites (H0s, c‐centres) next to Sr2+ in [110] in KCl is investigated by ENDOR and ENDOR‐induced ESR. The superhyperfine and quadrupole interactions and their relative signs of three types of inequivalent nearest Cl‐nuclei are determined. The transition energy for the first excited vibrational hydrogen state is derived from the superhyperfine temperature dependence. A further H0s, c‐centre is found with Sr2+ probably on a [200] site. The superhyperfine data are discussed considering the local lattice distortion around the cation vacancy.
Landau Model of a Spin Glass with Two Order Parameters: Stability and Derived Physical Properties I. Stability
Authors: Deutges D. , Heber G. 
Published: July 2007

AbstractA Landau‐type theory of phase transitions with two order parameters is used to describe modificated ferromagnetic and spin glass phases. Phase transitions to “normal” ferromagnetic or paramagnetic states are investigated. We shall be interested mainly in the conditions of stability and the resulting consequences for the choice of coefficients in the Landau free energy. The critical behaviour of the modificated ferromagnetic and spin glass phases against external magnetic fields is shown. Physical properties as susceptibility, magnetization, and specific heat are deduced by chosing suitable linear temperature dependences of the coefficients of the free energy. The competing phases are considered.
Antiferromagnetic Polarization Induced by Localized Moments in Metals
Authors: Oleś A. M. , Chao K. A. 
Published: July 2007

AbstractThe polarization of the conduction electron cloud around the impurity is investigated with a variational trial function for the Wolff model. When there is a local moment, an antiferromagnetic polarization is obtained. The polarization moment on the nearest neighbours of the impurity only partially compensates the impurity moment. That is in agreement with the long‐range nature of the polarization cloud.
Neutron Powder Diffraction Studies of Fluorite and Pyrochlore NdxZr1−xO2−x/2 Solid Solutions with 0.25<x<0.55
Authors: Van Dijk T. , Helmholdt R. B. , Burggraaf A. J. 
Published: July 2007

AbstractNeutron powder diffraction studies on stoichiometric and non‐stoichiometric pyrochlore phases of the ZrO2‐ Nd2O3 system show remarkable differences in the occupation factor of the 8b site of space group Fd3m to which the pyrochlore phase belongs. Stoichiometric Nd2Zr2O7 can be described as a perfect pyrochlore phase in which the 8b site is either vacant or at least has a low occupation factor. The occupation factors of the 8b sites of non‐stoichiometric NdxZr1−xO2−x/2 pyrochlores reveal that these contain a large degree of disorder in the anion sublattice. Best refinement results on non‐stoichiometric materials are achieved when the overall structure of the non‐stoichiometric pyrochlore phase is described as a hybrid phase consisting of a major volume fraction of the stoichiometric pyrochlore phase and a minor fraction of the defect fluorite phase.