bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Pinning Induced by Nickel Layers on Permalloy Films
Authors: Hoffmann F.
Published: July 2007

The dynamical pinning induced by thin layers of nickel on epitaxial permalloy films is investigated by stationary spin wave resonances at 17 and 35 GHz. The effective surface anisotropy is determined by comparing the location of resonance peaks for films without layer and for composite films. The high value and the d.c. field dependence of the effective surface anisotropy are attributed to the presence of exchange coupling between the films.
Spontaneous Raman Scattering by Polaritons. I. General Theory
Authors: Obukhovskii V. V. , Ponath H. , Strizhevskii V. L.
Published: July 2007

A general theory of Raman scattering (RS) by polaritons in anisotropic crystals with an arbitrary number of phonon branches is developed. A classification of possible scattering variants is given for both uniaxial and cubic crystals. Formulas defining the angular dependence of the integral intensity and scattering line shape are obtained. Some possible ways of determining the ratios of electronic—ionic and pure electronic contribution to the RS intensity are discussed. The scattering intensity by longitudinal phonon is also investigated.
Spontaneous Raman Scattering by Polaritons. II. The Case of CdS and LiNbO3 Crystals
Authors: Obukhovskii V. V. , Ponath H. , Strizhevskii V. L.
Published: July 2007

On the base of a general theory of Raman scattering (RS) by polaritons, previously developed by the authors, polariton RS in CdS and LiNbO3 crystals was calculated at scattering radiation with λ1 = 5145 Å and λ1 = 4880 Å, respectively. The angular dependences of RS line integral intensities and besides this for CdS the scattering line shapes were calculated. It is shown in particular that in the CdS scattering spectrum at small angles the auxiliary low‐frequency “photon‐like” line consisting of two similar components should appear besides the usual “phonon‐like” line. In LiNbO3 some scattering variants are studied at the excitation of nine phonon branches of E‐type and of four branches of AI‐type.
Ultramarine study by EPR
Authors: Więckowski A.
Published: July 2007

By EPR, ion‐radicals ˙S−,˙S, and ˙S are found to arise in the process of synthesizing ultramarine. Typical, blue ultramarine contains ˙S ions. At room temperature, the line width is found to be determined to a large extent by spin–lattice interaction, whereas at liquid nitrogen temperature (77° K) almost exclusively by spin–spin interaction. The EPR line shape was analyzed by linear anamorphosis of the resonance curve. The second moment was used for computing the density of polysulfide ions ˙S according to Van Vleck's formula. The results indicate that the ˙S radicals form a face centred cubic lattice in an elementary cell with lattice constant d′ = 2 d = 18.12 Å, where d is the lattice constant of the elementary cell determined by the X‐ray method.
An electron spin resonance study of photoproduced trivalent iron and divalent vanadium in silver chloride
Authors: Cheema S. U. , Smith M. J. A.
Published: July 2007

A method is described which allows Fe2+ and V3+ to be formed in the same specimen of silver chloride. Exposure to blue or to red light produces Fe3+ and V2+. The effect of blue light is explained in terms of hole capture by Fe2+ and electron capture by V3+ whereas that of red light is explained in terms of a charge‐transfer absorption by the trivalent forms of iron and vanadium. A re‐arrangement in the environment of Fe3+ occurs on warming to about 203° K. After blue irradiation at 93° K some of the V2+ is believed to be associated with two silver‐ion vacancies. A re‐orientation of the vacancies is observed on warming to about 110 and at about 150° K a further re‐orientation takes place and one vacancy is removed. Photoproduced Fe3+ and V2+ are stable at 93° K. At room temperature they decay at the same rate with a half life which is of the order of minutes.
Inelastic neutron scattering investigation of spin waves and magnetic interactions in α‐Fe2O3
Authors: Samuelsen E. J. , Shirane G.
Published: July 2007

Spin waves in antiferromagnetic α‐Fe2O3 have been studied at temperatures of 240 and 290° K by means of inelastic neutron scattering. We report here the first determination of the acoustical branch throughout the entire Brillouin zone and the first observation of the optical branch. The latter shows little dispersion throughout the zone, and has an energy of 1125° K (97 meV) at the zone centre. At the zone boundaries a gap of 20 to 70° K exists between the two branches. Heisenberg interaction parameters Jm defined through a Hamiltonian \documentclass{article}\pagestyle{empty}\begin{document}$ H\, = \, - \,\sum\limits_{i,j} {J_m } (r_{ij} )S_i \cdot S_j $\end{document} were obtained through fitting of the data to theoretical expressions for the dispersion relations. The following values were obtained for the first five nearest neighbours: J1 = 6.0 ± 1.6° K, J2 = 1.6 ± 0.6° K, J3 = −29.7 ± ± 2.0° K, J4 = −23.2 ± 1.0° K and J5 = −1.0 ± 1.0° K. Interactions to farther neighbours were found to be weak. Neutron intensity data were partly invoked in obtaining the interaction parameters, as two sets of parameters could fit the energy data almost equally well, but they predicted different relative intensities for the two branches in certain regions of the reciprocal space. All spin waves of energy larger than 80° K, including the entire optical branch, were found to be unaffected by the Morin spin‐flip transition at 261° K temperature. The spin‐wave data were used to calculate the sublattice magnetization, the Néel and the Curie‐Weiss temperatures, the perpendicular susceptibility at low temperatures and the density of spin‐wave state spectrum.
Diffusionsanisotropie in Eisen–Silizium‐Legierungen
Authors: Forsch K.
Published: July 2007

Die magnetfeldinduzierte Anisotropie wurde an FeSi‐Einkristallen mit 4,2; 6,7; 9,8 und 14 At% Si untersucht. Zwischen 50 und 350°C zeigt die Diffusionsanisotropie sowohl in [100]‐ als auch in [110]‐Richtung fast die gleiche Abhängigkeit von der Meßtemperatur wie die Kristallanisotropie. Die Zeitabhängigkeit der in einer Probe mit 4,2 At% Si in [100]‐bzw. [110]‐Richtung induzierten Anisotropie läßt sich gut durch eine einzige Relaxationszeit mit τ0 = 3 × 10−14±1.5 s und Q = (2,35 ± 0,2) eV beschreiben. Die Kristalle mit höheren Si‐Gehalten zeigen ein komplizierteres Verhalten.
Experimental verification of the theoretical model for the photoionization of deep impurity centres in semiconductors
Authors: Zavadskii Yu. I. , Kornilov B. V.
Published: July 2007

The wavelength dependence of the photoionization cross‐section (PCS) of the Zn acceptor level at Ev + 0.31 eV in silicon has been determined for temperatures of 85 and 290 °K from an investigation of the photoexcitation of holes from this level into the valence band. The experimental results are compared with the theoretical predictions based on a deep‐centre model using a short‐range potential. The agreement between theory and experiment is reasonable.
Fine structure of weak kinematical diffraction beams emerging from wedge‐shaped crystals
Authors: de Ridder R. , van Landuyt J. , Gevers R. , Amelinckx S.
Published: July 2007

The fine structure of a weak kinematical diffraction beam, due to the presence of a wedge shaped crystal part in the selected area, is derived by applying a Fourier transformation to the expression of the wave function deduced within the two‐beam kinematical theory. Also the correspondence between the fine structure of a weak beam and the dark field image, produced by this beam, is analysed. Two general types of wedges are considered: wedges formed by grain or twin boundaries and general genuine wedges bound by vacuum. The theoretical results for the fine structure caused by the two types of wedges are compared with experiments on twin boundaries in stainless steel and on MgO crystals. The observations are in very good agreement with the theory.
Effect of pressure on the curie points of the pseudo‐NiAs‐type Mn1+δSn
Authors: Ozawa K. , Ogawa M. , Yanagisawa S. , Anzai S.
Published: July 2007

Curie temperatures of Mn1+δSn, including interstitial Mn atoms in NiAs‐type structure, have been investigated using the magnetic induction method at hydrostatic pressures up to about 5 kbar. The magnetic induction smoothly diminishes at Tc (250 to 260 °K). No transition anomaly has been observed in electrical resistivity of Mn1.77Sn and Mn1.5Sn quenched from about 700°C. The values of specific resistivity are observed to be (4 ± 1) × 10−4 Ωcm at room temperature. The Curie temperatures increase linearly with increasing pressure at the rates of dTc/dp: +(2.0 ± 0.1) deg/kbar, +(1.5 ± 0.1) deg/kbar, and +(1.2 ± 0.1) deg/kbar for Mn1.77Sn quenched from 710, 480, and 380°C, respectively, and +(1.9 ± 0.1) deg/kbar for Mn1.5Sn quenched from 700°C. The positive pressure effect indicates that the exchange interaction is enhanced by decreasing the volume in Mn1+δSn. This deduces that the shift of Tc due to change of quenching temperature is explicable in terms of the volume effect of exchange interactions. It is also found that dTc/dp strongly depends on the quenching temperature, i.e. the ordered arrangements of Mn interstitial atoms, although little difference has been observed in dTc/dp between δ = 0.5 and 0.77 quenched from about 700°C.
Thermal expansion and volume change of crystals containing substitutional point imperfections
Authors: Timmesfeld K. H. , Elliott R. J.
Published: July 2007

The change in volume and thermal expansion coefficient of a crystal by the introduction of point defects is investigated. These effects have three contributions: 1. a change in the spring constants around the defect, 2. a change in anharmonicity around the defect, 3. the changed normal modes of the crystal containing defects. These three contributions partly cancel so that the resulting change in thermal expansion coefficient may be positive or negative. Especially in the case of the occurrence of a low frequency resonance a dip or bump in the low temperature region of the thermal expansion coefficient may occur.
Fine Structure of Electronic Spectra of Binary Substitutional Alloys in a Single‐Band Model
Authors: Čápek V.
Published: July 2007

The fine structure of the electronic density of states due to clusters of impurity atoms in disordered binary alloys is studied for a single‐band model with a short‐range random scattering potential. The sum of the n‐centre contributions to the total T‐matrix is obtained for n = 1, 2, 3. The T‐matrix describes the scattering corrections to an optimum one‐centre approximation which is determined self‐consistently in each case. For n = 1, the method is identical with the coherent potential approximation (CPA). Comparison of the results for n = 1 and n = 2 gives a criterion for validity of the CPA. A simple one‐dimensional model is studied numerically in the two‐centre approximation and the results are compared with the CPA and the direct solution for a finite chain.
Neutron Diffraction Study of Ni(OH)2
Authors: Szytula A. , Murasik A. , Balanda M.
Published: July 2007

A synthetic polycrystalline sample of Ni(OH)2 was investigated by means of neutron diffraction in the temperature range 4.2 to 293 °K. The crystallochemical structure of this compound is analogous to the structure of Ca(OH)2. At temperatures below 28 °K Ni(OH)2 is antiferromagnetic with magnetic moments directed parallel to the c0‐axis.
Relativistic Energy Bands of HgTe and HgSe
Authors: Overhof H.
Published: July 2007

The electronic band structures of HgTe and HgSe have been calculated using the relativistic Green's function method. The results are compared to reflectivity data. Particular care was taken to calculate the details of the band structure in the vicinity of the band gap. A valence band overlap is found which is in agreement with the estimate given by Vérié.
The F Center in KCl Crystals Part I: Formation and Bleaching Kinetics
Authors: Aegerter M. A. , Lüty F.
Published: July 2007

A quantitative analysis of the higher transitions of the M center in the UV up to 5.0 eV in KCl crystals with high [M] : [F] ratio and unaligned and aligned M centers shows several new excitations (“LM bands”). Assuming that the LM excitation leads to conductive states, a simple electron kinetic model shows that UV irradiation of the F + M center system produces ionized F and M centers (α and F) while competing capture processes partially destroyed them or form F' and M' centers. The F center production spectrum should closely follow the absorption ratio of LM:LF while the bleaching spectrum should follow the F' and M' spectrum. Experimental confirmation of this model is presented. By X‐raying the crystal (containing F + M centers) at LHeT, extra electron traps are introduced into the crystal and shift the equilibrium of the reaction to higher amount of F center, which are not stabilized by F' and M' centers. These extra F centers anneal out near 40 °K in parallelity with the third stage annealing of X‐ray produced α‐centers‐interstititals anions.
The Magnetic and Structural Properties of Bulk Amorphous and Crystalline Co‐P Alloys
Authors: Simpson A. W. , Brambley D. R.
Published: July 2007

Bulk samples, of the order 0.2 mm thick, of cobalt‐phosphorus alloys have been prepared by prolonged electroless deposition with phosphorus contents varying from 5 to 9 at%. Alloys with less than 8.8 at% were found to be crystalline with a single‐phase h.c.p. structure, and those with 9 at% were amorphous. The saturation magnetization, magnetostriction, coercivity, and susceptibility of the crystalline alloys varied uniformly with phosphorus content. The amorphous alloys had significantly different magnetic properties from the crystalline ones of similar composition; in particular the susceptibility was nearly two orders of magnitude greater. This greater susceptibility was predominantly associated with the absence of magnetocrystalline anisotropy in the non‐crystalline material. On annealing, the amorphous material first transformed to a single‐phase h.c.p. structure similar to that of the crystalline alloys, and at a higher temperature to the equilibrium two‐phase structure of a cobalt‐rich h.c.p. phase and an orthorhombic Co2P phase. The susceptibility of the amorphous alloy fell by a factor of 15 times on annealing. This was attributed to the introduction of crystalline order and hence magneto‐crystalline anisotropy.
Behaviour of Primary Defects in Electron‐Irradiated Germanium
Authors: Bourgoin J. , Mollot F.
Published: July 2007

An investigation is made of the influence of the free electron and donor impurity concentrations on the annealing kinetics of the 35 and 65 °K stages and on the creation rate of the 35 °K stage, in low temperature electron irradiated n‐type Germanium, using As‐ or Sb‐doped samples, Ga and Cu compensated samples, and a Li‐doped sample. The results obtained allow to conclude that the mobility of the Ge interstitial occurs at 4.5, 27, and 65 °K, depending on its charge state and the mobility of the vacancy at 90 °K, and to identify the defect associated with the 35 °K stage as a vacancy‐interstitial pair where the interstitial is a donor impurity (annealing through the interstitial mobility). This interstitial mobility, strongly dependent on the charge state, explains radiation annealing and the behaviour of irradiated p‐type Germanium.
Magneto‐Reflectivity Measurements on Exciton Bands in CuCl
Authors: Staude W.
Published: July 2007

The influence of an external magnetic field on the normal incidence reflectivity of CuCl single crystals has been measured in the Voigt and Faraday configurations. The results are discussed in terms of the dielectric function calculated from the reflectivity spectrum by a Kramers‐Kronig transformation. In the Voigt configuration two new exciton bands can be observed, which are attributed to a triplet and a longitudinal exciton. Their energetic positions are used to determine the parameters of electron‐hole exchange interaction in the 1s excitons, and the spin‐orbit splitting parameter of the upper valence band. The excitonic g‐values are determined from the Faraday configuration measurements and can be interpreted on the basis of the tight binding model.
Stress Relaxation Testing and the Determination of the Internal Stress
Authors: Lloyd D. J. , Embury J. D.
Published: July 2007

The use of stress relaxation methods to establish the parameters describing dislocation mobility have been critically examined. It is shown that the values of internal stress established from the condition of zero relaxation rate are temperature independent and equivalent to the athermal component of the flow stress. The various methods of establishing the internal stress are in accord providing cogniscence is taken of the experimental limitations of the technique.
Magnetostriction of Antiferromagnetic Cr2O3 in Strong Magnetic Fields
Authors: Dudko K. L. , Eremenko V. V. , Semenenko L. M.
Published: July 2007

The magnetostriction of antiferromagnetic Cr2O3 has been measured in a magnetic field directed along the crystal symmetry axis. In the field H
c = 60 kOe which corresponds to a spin‐flip transition we have observed jumps in the crystal sizes. The deformation along the symmetry axis is 2.8 × 10−5 and the relative volume change is 2.0 × 10−5. The form of the magnetostriction curves may be accounted for by the dependence of magnetic anisotropy energy on the interatomic distances. The calculation of magnetic dipole interaction in the given crystal provides jump values which are considerably lower than those observed. The contributions to the magnetic anisotropy energy arising from considering the spin‐orbit coupling are assumed to be important for magnetoelastic properties of Cr2O3.
Second‐Harmonic Generation and the Ordering Reaction in NH4Cl
Authors: Bartis F. J.
Published: July 2007

The order‐disorder transformation in ammonium chloride is taken to be a first‐order phase change. The asymptotic behavior of the second‐harmonic intensity is determined on the assumption that the growth of the ordered domains is controlled by the stress field around crystal defects. By a suitable choice of the characteristic temperature T0 the data can be reconciled with nucleation along edge dislocations. The location of T0 relative to the hysteresis region suggests that the irreversibility of the transition is associated with the formation of vacancies.
Thermal expansion, heat capacity, and compressibility of solid CO2
Authors: Manzhelii V. G. , Tolkachev A. M. , Bagatskii M. I. , Voitovich E. I.
Published: July 2007

The coefficients of thermal expansion (13 to 139 °K), heat capacity (2 to 20 °K), and velocity of longitudinal and transversal ultrasonic waves (88 to 190 °K) for solid CO2 have been determined along the solid‐vapour equilibrium line. Heat capacity of constant volume, adiabatic and isothermal compressibilities, the Grüneisen and Poisson coefficients were calculated using the above data. The contributions of various types of heat motion to heat capacity, thermal expansion and compressibility have been separated, and the parameters of isolated orientational defects in crystalline CO2 determined. The connection between the orientational defect parameters and the extent of non‐centricity of intermolecular interactions in solids is discussed.
Influence of electron‐electron scattering on the anisotropic conductivity at high electric fields in Si
Authors: Asche M. , Boichenko B. L. , Bondar V. M. , Sarbei O. G.
Published: July 2007

The conductivity and its anisotropy were investigated in dependence on the electric field strength in a wide range of impurity density for n‐Si at 77 °K. It is shown that the intervalley transfer of electron energy on account of electron‐electron interaction has to be included for carrier densities above 1015 cm−3 in order to achieve a satisfactory description of the results obtained experimentally.
Density of states in ordered and disordered ferromagnetic thin films
Authors: Goedsche F.
Published: July 2007

The density of spin‐wave states in ordered and disordered linear Heisenberg chains is investigated. The disorder is introduced by setting random quantities for the exchange integrals. The model also includes the effect of surface spin pinning and variations of the exchange integrals near the film faces upon the spectrum. Surface modes as well as the bulk spectrum for both types of order are discussed.
Torsional vibrations of H2O molecules in crystalline Li2SO4·H2O
Authors: Janik J. M. , Janik J. A. , Pytasz G. , Wasiutyński T.
Published: July 2007

Results of IR and Raman measurements for Li2SO4·H2O and Li2SO4·D2O are reported and compared with neutron inelastic scattering data. Bands at about 320,580, and 850 cm−1 are interpreted as connected with H2O torsions. A group theory analysis of the torsional vibrations of H2O molecules in the crystal is given.
Temperature dependence of the singlet‐triplet absorption band in molecular crystals
Authors: Zgierski M. Z.
Published: July 2007

It is suggested that the temperature dependence of the intensity distribution among vibrational peaks in the singlet‐triplet absorption spectrum of molecular crystals can be explained by the dependence of the electronic wave function of a molecule contained in a crystal on the position coordinates of the centre of a molecule.
A simple model for amorphous antiferromagnets
Authors: Hasegawa R.
Published: July 2007

A 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

The 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

Dislocations 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

An 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

Shifts 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

For 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

An 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

The 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

Magnetisierungskurven 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

Conductivity 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

It 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

The 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

The 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

Experimental 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

A 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

A 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

Nous 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

The 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

The 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

Co57‐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

Starting 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

The 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

Using 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.
On the Dynamics of Surface Atoms
Authors: Iosilevskii Ya. A.
Published: July 2007

The surface Debye frequencies for the matrix and impurity atoms are calculated in the total range of physically allowed parameters of the elastically isotropic solid. The statistical weights of the surface and volume modes are found.
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

The 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

The 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

The 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

Nuclear 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

A 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

A 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

The 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.
Theory of the elastic and inelastic scattering of light by magnetic crystals. II. Second‐order processes
Authors: Le Gall H. , Vien Tran Khanh , Desormière B.
Published: July 2007

The second quantization of the magneto‐optical interactions in ferromagnetic crystals is extended to second‐order processes. From the electric and magnetic dipole transitions induced by an incident radiation, the evolution of the electromagnetic field is analysed in the cases of bi‐gyrotropic and quadratic magneto‐optical materials. The physical and analytical relations between the elastic (linear magnetic birefringence) and inelastic (two‐magnon Raman effects) scatterings are derived from the second‐order magneto‐optical Hamiltonians. It is shown that the two‐magnon Raman susceptibility is proportional to the second power of the specific linear magnetic birefringence. In isotropic media the second‐order magneto‐optical interactions may be separated in an isotropic (or scalar) part and in an anisotropic (or tensorial) part. From the corresponding Hamiltonians the polarization rules are deduced for the second‐order inelastic scatterings. In ferrites and orthoferrites the first‐ and second‐order magneto‐optical constants may have equivalent values. As supported by experiments the influence of the quadratic magneto‐optical interactions on the first‐order inelastic scattering is shown from the magneto‐optical polarization and Hamiltonians. The one‐magnon Stokes component may be higher than the anti‐Stokes component when the polarization of the incident photons is parallel to the dc magnetization. The opposite result is obtained with light polarized perpendicular to the dc magnetization. The one‐magnon Raman Hamiltonians and susceptibilities modified by the quadratic effects are derived from the optical polarization and compared with experimental data.
Stabilization of aliovalent ions observed by Mössbauer emission spectroscopy in 57Co‐doped simple ligand compounds
Authors: Cruset A. , Friedt J. M.
Published: July 2007

The Mössbauer emission spectra of 57Co2+ in MgF2, CaF2, K2CoF4, and MgCl2 have been studied. Aliovalent charge states (Fe3+) have been observed in several of these salts. A general thermodynamic model, based on the correlation between the proportion of Fe3+ ions and the Madelung potential at the cation site in the host, is proposed to account for the stabilization of various iron species after 57Co electron capture in simple ligand compounds.
Inelastic impurity scattering of hot electrons in semiconductors
Authors: Kachlishvili Z. S.
Published: July 2007

The field and concentration dependences of the mobilities as well as the field dependences of the free carriers and conductivity have been calculated taking inelastic impurity scattering of hot electrons (the 1s‐2p excitation and the ionization of neutral impurities) into account. Besides the dependence of the breakdown field on the neutral impurity concentration has been estimated. The agreement with the experiment is satisfactory.
Numerical behaviour of transmission and derivative traces due to direct electronic transitions near van hove singularities
Authors: Doran N. J. , Harper P. G.
Published: July 2007

Analytical forms of the complex dielectric function ε(ω) near each of the singular (Van Hove) critical points are given for the allowed and forbidden transitions at arbitrary light polarizations. By numerically simulating ε(ω) the characteristic traces of the transmission T(ω) and its derivatives dT/dω, d2T/dω2 have been obtained over a range of refractive index n, k values. From these it has been found possible to tabulate the possible Van Hove singularities corresponding to a given characteristic trace.