bluuebunny/crossref_metadata_2025_split huggingface dataset:
A simple model for amorphous antiferromagnets
Authors: Hasegawa R. 
Published: July 2007

AbstractA molecular field model for amorphous antiferromagnets is considered by taking into account the structural fluctuations which could exist in amorphous materials. The results show that the fluctuations shift the susceptibility versus temperature curves towards or away from the temperature axis with changes in the Néel temperatures. The direction of the shift depends on the sign and on the size of the fluctuations in the exchange integrals. The present results are consistent with the magnetic properties of an amorphous MnPC alloy.
Study of the nuclear‐spin‐lattice relaxation of 23Na in the paraelectric and ferroelectric phase of NaNO2
Authors: Avogadro A. , Cavelius E. , Müller D. , Petersson J. 
Published: July 2007

AbstractThe nuclear‐spin‐lattice relaxation time T1 of 23Na in NaNO2 single crystals is measured between room temperature and 200 °C. The experimental method employed consists of a very long saturation sequence of 90° pulses. The results indicate the existence of a logarithmic singularity of the relaxation rate if the phase transition is approached from both the paraelectric and ferroelectric phase. In addition a discontinuity of T1 is observed at the transition of the paraelectric‐antiferroelectric type. The critical behaviour of the spin‐lattice relaxation rate of 23Na in NaNO2 is described, theoretically by applying the thermodynamics of the ferroelectric phase transition.
A unified six‐dimensional treatment of elastic green's functions and dislocations
Authors: Malén K. 
Published: July 2007

AbstractDislocations together with forces in infinite elastic media are treated in a six‐dimensional formalism. Expressions for the displacement fields of point sources (i.e. the elastic Green's function), of elementary dislocation loops and of straight dislocations and line forces are given both for the static case and for uniform motion. The connection with similar expressions given by others is shown. The relations between matrices, eigenvectors, and eigenvalues are studied. The formalism developed simplifies the evaluation of perturbation expansions and derivatives. It is shown that the same eigenvalue problem appears for different sources suitably chosen.
The mössbauer spectra of substituted systems local molecular field theory
Authors: Coey J. M. D. , Sawatzky G. A. 
Published: July 2007

AbstractAn insulator with two different magnetic ions distributed in several crystallographic sites is considered in the molecular field approximation. As an example a material containing a random distribution of iron and a non‐magnetic ion in equivalent sites is studied, assuming that the superexchange between an iron ion and cations on six nearest‐neighbour sites is the dominant interaction. Provided that a small longer range interaction is present, the Mössbauer spectra predicted for different non‐magnetic concentrations at various temperatures are in agreement with experimental observation except just below the magnetic ordering temperature.
Effect of pressure on the curie point of Cr7□Te8 with the NiAs‐type structure
Authors: Ozawa K. , Yoshimi T. , Yanagisawa S. 
Published: July 2007

AbstractShifts of the Curie temperature of a disordered and an ordered phase in Cr7□Te8 including MLD have been investigated by magnetic induction measurements at hydrostatic pressures up to 5 kbar. The relative magnetization vanishes at the Curie temperature, TC = 343 and 332 °K for the disordered phase (1000 °C) and the ordered phase (400 °C), respectively, at atmospheric pressure. The Curie temperature shifts to lower temperature with increasing pressure at the rate of dTc/dP = −(6.3 ± 0.2) deg/kbarfor Cr7□Te8 (1000 °C)The temperature in parenthesis denotes the quenching one.
and dTc/dP = −(5.6 ± 0.4) deg/kbar for Cr7□Te8 (400 °C), determined from magnetic induction measurements. A certain extent difference in pressure effects dTc/dP was observed between the disordered and the ordered phase. This fact implies that the pressure effect on TC is remarkably influenced by the arrangement of MLD in the crystal lattice. The observed difference, ΔTc = 10 deg in the Curie temperature due to a change in the quenching temperature, is explained by the volume effect of exchange interaction in the interatomic spacing. The dependence of nonstoichiometric parameter δ on the exchange mechanisms in Cr7□Te8 is briefly discussed.
Forbidden transitions (δM = 2) induced by an axial crystal field in electron paramagnetic resonance of 3d5 ions in II–VI compounds
Authors: Clerjaud B. , Marti C. , Billmann A. 
Published: July 2007

AbstractFor certain angles between the magnetic field and the c‐axis of the crystal, “forbidden” magnetic dipolar transitions ΔM = 2, Δm = C, ± 1 (M and m electronic and nuclear azimuthal quantum numbers) can be induced by an axial crystal field in electron paramagnetic resonance. These transitions are observed in ZnS/Mn2+, ZnO/Fe3+, and ZnO/Mn2+ single crystals and compared with theoretical and experimental results.
Vibronic spectra of molecular crystals with participation of non‐totally symmetrical vibrations
Authors: Serikov A. A. 
Published: July 2007

AbstractAn investigation is made of the vibronic spectra of molecular crystals for the case of a combination of the electronic excitation with the non‐totally symmetrical intramolecular vibration. It is shown that, depending on the crystal characteristics determining the values of the theoretical parameters, the excited states of the molecules in the crystal in the electronic‐vibrational frequency range can correspond with : a) vibronic excitons (stable or unstable) and, along with them, two‐particle excitations corresponding to the formation of electronic excitons and intramolecular phonons; b) localized electronic‐vibrational excitations (stable or unstable) of the groups of neighbouring molecules and, along with them, two‐particle excitations corresponding to an electronic excitation of one of the crystal molecules, and a phonon exciton. The shape of the absorption spectra as well as the intensities of the absorption bands corresponding to the different types of excitations are calculated.
On the correlation effects in the Landau‐Pekar polaron method
Authors: Sikivie P. , Kartheuser E. , Evrard R. 
Published: July 2007

AbstractThe conservation of total angular momentum is considered in detail for polarons, using an expansion of the polarization field into spherical waves. This formalism is used to improve the Landau‐Pekar approximation, taking the electron‐phonon correlations partially into account. A value 10 to 20% lower is obtained for the polaron ground state energy for values of the coupling constant α ranging from 8 to 5.
Magnetisierungskurven von Supraleitern zweiter Art mit kleinen Ginzburg‐Landau‐Parametern
Authors: Kumpf U. 
Published: July 2007

AbstractMagnetisierungskurven von homogenen Blei‐Thallium‐Einkristallen mit Ginzburg‐Landau‐Parametern 1/\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt2 $\end{document} ≦ ϰ ≦ 1,8 (Supraleiter 2. Art) zeigen bei Hc 1 ein plötzliches Eindringen des magnetischen Flusses bis zu einer Anfangsinduktion B0. Dies entspricht dem in diesen Materialien beobachteten Gleichgewichtsabstand d0 der Flußlinien in der Shubnikov‐Phase. Dieses Verhalten kann nur durch die Annahme einer bis jetzt noch unbekannten, weitreichenden, anziehenden Wechselwirkung zwischen den Flußlinien erklärt werden. Die Untersuchungen der Temperatur‐ und ϰ‐Abhängigkeit der Anfangsinduktion B0 erlauben Aussagen über den Gültigkeitsbereich der Ginzburg‐Landau‐Theorie.
Conductivity and thermoelectric power of trigonal SexTe1−x single crystals
Authors: Beyer W. , Mell H. , Stuke J. 
Published: July 2007

AbstractConductivity σ and thermoelectric power α of SeTe mixed crystals have been measured in the temperature range from 100 K up to the melting points. The activation energy of the intrinsic conductivity shows a relatively complicated dependence on alloy composition, which can be explained by a transition from the direct gap of Te to the indirect gap of Se at about 40% Se content. The extrinsic conductivity has an activation character in a large part of the system. Formally the activation energy ΔE has to be attributed to the mobility. It decreases continuously towards Te and vanishes at the high Te end. ΔE can be explained by a strongly inhomogeneous hole concentration as for trigonal Se. The density of states mass of holes has been estimated, which increases approximately linearly with Se content from 0.2 m0 for Te to about 1.4m0 for Se.
Disalignment of the g‐ and fine structure tensor axes in the ESR spectra of some copper compounds
Authors: Buluggiu E. , Dascola G. , Giori D. C. , Varacca V. 
Published: July 2007

AbstractIt is shown that for an effective spin S′ = 1 arising from the coupling of two spins S = 1/2 the axes of the g‐tensor and of the fine structure tensor may have different orientations. A phenomenological theory is given that explains the effect on the base of exchange interaction. The experimental results for single crystals of two cupric compounds are reported.
Lattice dynamics of lead: An elastic force model approach
Authors: Gupta H. C. , Tripathi B. B. 
Published: July 2007

AbstractThe lattice dynamics of lead is discussed within the framework of elastic force models which include volume forces in addition to the central and the angular ones. The volume forces have been taken on the lines of Sharma and Joshi, while both Clark, Gazis, and Wallis (CGW) type of angular forces and that of de Launey (DAF) type have been used. The results of the phonon dispersion curves and the Debye temperatures have been compared with the experimental ones. The agreement obtained with both the angular force models is satisfactory. In the phonon dispersion curves, Kohn anomalies are seen using the DAF type angular force model but not using the CGW type. It is shown that the CGW model gives better results than the DAF one.
Optical anisotropy of ZnO in the ultraviolet region
Authors: Klucker R. , Nelkowski H. , Park Y. S. , Skibowski M. , Wagner T. S. 
Published: July 2007

AbstractThe reflectivity of ZnO single crystals was measured at near normal incidence in the energy region from 3 to 25 eV with linearly polarized light, the electric field vector lying perpendicular and parallel to the c‐axis. From the reflectivity the optical constants n and k, the complex dielectric constant ε = ε1 ε i ε2 and the energy loss function L = |Im ε−1| have been computed by a Kramers‐Kronig analysis for both directions of polarization. The profiles of the spectra differ completely from those of other II–VI compounds of the wurtzite structure. The energetic positions and the polarization dependence of the peaks in the reflectivity and the ε2 spectra can be related to the results of the first complete band structure calculation accomplished by Rössler using the Korringa‐Kohn‐Rostocker method.
Investigation of Anomalous Transmission of X‐Rays in the General Case of Laue Diffraction
Authors: Kovev E. K. , Novikova L. P. , Efimov O. N. 
Published: July 2007

AbstractExperimental integral characteristics of the anomalous transmission of X‐rays for unsymmetrical Laue diffraction and for crystals with a centre of symmetry were obtained using the example of (220)‐reflection of Si single crystals. The integral characteristics for crystals without a centre of symmetry were investigated for unsymmetrical (111)‐reflections of InAs single crystal. The data obtained agree well with the results of theoretical considerations published earlier [1].
Extension of the Mollwo‐Ivey Relation for Impurity Centres in Alkali Halide Crystals
Authors: Sethi V. C. , Karguppikar A. M. , Tyagi R. C. 
Published: July 2007

AbstractA Mollwo‐Ivey type relation has been obtained empirically, which predicts the absorption bands for thallium (Tl+) in different alkali halide crystals. The values of the exponent n and constant K (in Mollwo‐Ivey relation i.e. EF = K Rn) depend upon the ionic radii of the host and the impurity ions.
A Particular Many Beam Situation in Transmission Electron Diffraction
Authors: Serneels R. , Gevers R. 
Published: July 2007

AbstractA systematic analytical and numerical study is made of the many beam situation where the reciprocal lattice vector 2 g is in exact Bragg orientation. Absorption effects are neglected. In a first part the three beam case (0, g, 2 g) is studied for different electron accelerating potentials. Analytical expressions for the amplitudes and intensities of the different beams are derived. Special attention is also given for the energy dependence of the eigenvalues and eigenvectors of the dynamical matrix. In a second part the influence of the systematic reflections 3 g and −g is investigated. Intensity calculations are performed to check the efficiency of the three beam calculations at different electron energies and for different types of reflections.
Effet Voigt‐Cotton‐Mouton en région d'absorption dans les cristaux non magnétiques dopés
Authors: Boccara A. C. , Moreau N. 
Published: July 2007

AbstractNous présentons des résultats théoriques et expérimentaux concernant le dichroïsme linéaire magnétique (effet Voigt‐Cotton‐Mouton) de substances dia‐ ou paramagnétiques. Nous étudions le cas de centres cubiques ou uniaxes orientés et considérons en particulier l'influence des éléments de matrice non diagonaux de l'hamiltonien Zeeman. Les résultats expérimentaux obtenus pour Nd3+ dans CaWO4 sont en bon accord avec la théorie proposée.
The Second Order Magnetoelectric Effect in Yttrium Iron Garnet
Authors: Cardwell M. J. 
Published: July 2007

AbstractThe coefficient characterising the second order magnetoelectric effect in YIG has been measured over the temperature range 100°K to the Curie point. Two mechanisms have been proposed to explain the origin of this effect and the temperature dependence calculated using a two sublattice model shows quantitative agreement with experiment.
A Curvature in the Arrhenius Plot for the Diffusion of Iron in Single Crystals of Nickel in the Temperature Range from 1200 to 1400°C
Authors: Bakker H. , Backus J. , Waals F. 
Published: July 2007

AbstractThe diffusion of Fe‐59 in single crystals of nickel was measured in the temperature range from 1200 to 1400°C. The Arrhenius plot exhibits a clear curvature. The addition of iron impurities up to 1.5 at% had only a slight influence on the nickel self‐diffusion coefficient, while a measurement of the isotope effect for the diffusion of Fe‐55 and Fe‐59 at 1330°C yielded a quite “normal” value. The curvature in the In D versus 1/T plot for the diffusion of iron in nickel could not be explained.
Hyperfine Fields at Fe57 in Nickel–Manganese Alloys
Authors: Chandra G. , Radhakrishnan T. S. 
Published: July 2007

AbstractCo57‐doped alloys of nickel with manganese in the concentration range 0 to 33 at%, have been studied using Mössbauer spectroscopy at 77°K and some higher temperatures. The alloys were suitably heat treated for maximum ordering. The alloys with small Mn concentration showed simple magnetic h.f.s. while the higher concentration alloys exhibited complex behaviour. This is attributed to the co‐existence of long‐range ordered and disordered phases and accordingly these spectra could be resolved into contributions originating from two Fe57 sites by least squares fitting. A further check was obtained by disordering an alloy near Ni3Mn by quenching from 800°C, whereupon a simple h.f. pattern resulted. The Fe57 hyperfine fields in these alloys as a function of Mn concentration showed no variation except in the case of the long‐range ordered phase near Ni3Mn where the field was higher by about 20%. incidentally, the saturation magnetic moment of the alloy also showed a maximum in this region. It is shown that the Co57 atoms are likely to occupy the nickel sites in the case of the ordered stoichiometric alloy Ni3Mn.
Collective Oscillations of Atomic Electrons in the Statistical Theory of Atoms
Authors: Ishmukhametov B. Kh. 
Published: July 2007

AbstractStarting from the integral equation for the self‐consistent potential it is shown that the eigenfrequencies of the collective oscillations form a discrete spectrum. According to the calculations for argon the spectrum covers a rather narrow band of frequencies 3×1016S−1≦ ≦ ω ≦ 1017 S−1. The value of the estimated damping decrement γ ≈ 7 × 1015 S−1 indicates that at frequencies of about 1017 S−1 the proposed plasma mechanism will be predominant in the absorption and emission processes of radiation. It is expected that the considered collective states may be observed in X‐ray emission and absorption spectra of solids as well as of gases.
Empirical Relations of the Hilsch and Pohl Law Type in Alkali Halides
Authors: Serban T. 
Published: July 2007

AbstractThe effective Madelung energy of a transition leading to the generalization of the law of Hilsch and Pohl is defined. A very simple empirical method is given for the determination of the effective Madelung energy of a transition in crystals. The method enables to estimate the position of the maxima for bands α, β, U(H−), I−, A(Tl+), B(Tl+), C(Tl+), D(Tl+), C(Ag−), etc. Also, valuable indications are obtained regarding the nature of transition and the mode of participation of the lattice ions in the transition.
Screening of a Fixed Charge in the Modified Hubbard Approximation
Authors: Pathak A. P. 
Published: July 2007

AbstractUsing a modified Hubbard approximation for the static dielectric function, numerical calculations of the screening charge density around a fixed foreign charge in an electron liquid are presented for values of rs corresponding to the metallic density range. The screening parameter has been taken to reproduce the compressibility limit properly. The results are compared with those based on the original Hubbard approximation as calculated by Langer and Vosko, and it is found that the difference is small but not negligible.
Diffusion of Anisotropic Point Defects in Cubic Crystals in the Presence of a Field of Force
Authors: Kronmüller H. , Frank W. , Hornung W. 
Published: July 2007

AbstractThe diffusion equation for the migration of low‐symmetry point defects in the presence of a field of force has been derived. The discreteness of the lattice and the capability of reorientation of the symmetry axes of the defects were taken into account. An essential point of this description is that different interaction energies in the equilibrium and the saddle‐point configurations could be accounted for. The equations for the diffusion of tetragonal and crowdion interstitials in cubic crystals are presented.
The Effects of Short‐Range Order and Long‐Range Order on the Equilibrium Configuration of Superdislocations in FeCo : 2 at% V — Consequences on Flow Stress
Authors: Moine P. , Eymery J. P. , Grosbras P. 
Published: July 2007

AbstractThe variations in flow stress of FeCo : 2 at% V as a function of test or quench temperature exhibit a maximum near the critical temperature for ordering, Tc. Transmission microscope study of thin foils reveals the existence of paired dislocations not only at temperatures below Tc but also at temperatures above Tc where only short‐range order exists; calculations of their equilibrium spacing using the quasi‐chemical theory [6] are in agreement with experimental results. The peak in flow stress may be explained assuming that for high values of S (S is the long‐range order parameter) the dislocation sources are constituted by paired dislocations which keep parallel configurations when operating, and that for low values of S (or S = 0) sources are constituted by single dislocations or by paired dislocations with only one of them operating.
The Influence of Temperature on Slip Behaviour of Molybdenum Single Crystals Deformed in Tension in the Range from 293 to 573 °K .II. Slip Geometry and Structure of Slip Bands
Authors: Richter J. 
Published: July 2007

AbstractThe slip line pattern of molybdenum single crystals deformed in tension at temperatures between 293 and 573 °K (T/Tm = 0.1 to 0.2) was systematically investigated using optical and electron microscopy. The transition from parabolic stress‐strain behaviour to three‐stage hardening which occurs in a transition range Tt ≈ 340 to 400 °K [1] is associated with a basic change in the slip line pattern. At temperatures T < Tt multiple slip occurs whereas for T > Tt single slip in stage I is characteristical. For T > Tt the slip lines are pronounced wavy or zigzag‐like indicating that at elevated temperatures cross‐slip is an important slip process. Furthermore, composite slip on non‐parallel {110} planes was found at temperatures T > Tt. The observations suggest that the influence of temperature on slip line pattern results from the strong increase of mobility of screw dislocations with increasing temperature.
Nuclear Magnetic Resonance in Non‐Crystalline Tellurium
Authors: Koma A. , Mizuno O. , Tanaka S. 
Published: July 2007

AbstractNuclear magnetic resonance of 125Te in rapidly solidified tellurium has been observed, and a new line has been found which seems to come from the non‐crystalline (amorphous) part in the specimens. The structure of non‐crystalline tellurium is discussed on the basis of the experimental results.
The Lattice Dynamics of the Hexagonal Close‐Packed Metals
Authors: Trott A. J. , Heald P. T. 
Published: July 2007

AbstractA Born‐von Kármán model of the hexagonal close‐packed lattice, which includes a combination of central and angular forces extending out to third nearest neighbours, is used to study the harmonic properties of beryllium, magnesium, and zinc. The phonon dispersion curves and frequency spectra of these metals are computed and compared with previous experimental and theoretical results.
Energy band structures of Cd3P2 and Zn3P2
Authors: Lin‐Chung P. J. 
Published: July 2007

AbstractA pseudopotential energy band calculation is carried out for a hypothetical crystal which corresponds to Cd3P2 and Zn3P2. From these results, the conduction band effective masses as well as the interband transition assignments associated with the optical reflectivity peaks are deduced. The temperature dependence of the energy gap for these materials is estimated and dEg/dT is shown to be negative.
On the stability of different cubic lattices for the ionic compounds of AC‐type
Authors: Vukcevich M. R. 
Published: July 2007

AbstractThe stability of cubic CsCl, NaCl, and ZnS type lattices at zero pressure is considered. Assuming completely ionic bonding and Huggins‐Mayer repulsion potential, the lowest‐energy criterion and the mechanical stability conditions are combined into a new stability criterion. The combined criterion is presented in a form of a diagram which is divided into the stability regions for the three cubic lattices, in terms of two parameters: the range of repulsive forces and the difference between ionic radii. Data on all alkali halides and eight compounds of zinc and cadmium are compared with theory. In 25 cases, out of 28 considered, the combined stability criterion correctly predicts the stable lattice. In the three cases where the theory fails the measured elastic constants disagree with the Cauchy relations to such an extent that the central force model is, presumably, inadequate. In addition, diagrams are presented in which the elastic constants of all three cubic structures are plotted as functions of the range of the repulsive forces and the difference in ionic sizes.