bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic Circular Dichroism of Coe2+ ‐Doped Cubic Crystals
Authors: Douglas I. N. 
Published: July 2007

AbstractThe magnetic circular dichroism (MCD) and absorption spectra of Co2+ ions in MgO, CaO, SrO, and LiF crystals have been measured in the region from 12500 to 30000 cm−1. Most of the features in the MCD of MgO, CaO, and LiF crystals can be attributed to single Co2+ ions at sites of octahedral symmetry. In MgO some additional MCD features produced by Co2+Co2+ pairs are identified by their temperature independence. Although SrO has the same crystal structure as the other crystals, the Co2+ ions occupy trigonal sites (from EPR measurements) and the MCD and absorption spectra reflect this lowering of the symmetry.
Studies of the Band Structure of NbO by X‐Ray Photoelectróh Spectroscopy
Authors: Honig J. M. , Sinha A. P. B. , Wahnsiedler W. E. , Kuwamoto H. 
Published: July 2007

AbstractX‐ray photoelectron spectra are reported for single crystals of NbO in the binding energy range of −5 to +540 eV with respect to the Fermi level; the results are correlated with band structure schemes reported in the literature. A substantial electron density at the Fermi level in a very wide conduction band reported here is consistent with the highly metallic characteristics of the compound. Observations of spectra of Ar ions imbedded in the NbO matrix yield a work function of 6.45 eV for NbO.
Construction of the Reciprocal Fourth‐Rank Tensors in Crystals
Authors: Iosilevskii Ya. A. 
Published: July 2007

AbstractA simple covariant method is suggested to construct in a covariant form reciprocal quan‐ tities from the fourth‐rank tensors Xiklm, which describe arbitrary physical properties of single crystals invariant under the point symmetry group of the given crystal and the permutations i ⇄ k and l ⇄ m. The problem is solved for all crystal systems.
Polarizability of an Electron Trapped by an Interstitial Ion
Authors: Hattori K. 
Published: July 2007

AbstractA variational method is used to determine the polarizability of an electron trapped by an interstitial ion in an ionic crystal. An analytic result for the polarizability is obtained and it reduces to 4.5 in at. units, the exact value of the polarizability for the hydrogen atom. The polarizabilities in alkali and silver halides are evaluated.
Effects of Three‐Body Interactions on Hyperfine Fields
Authors: Manohar C. , Kelkar V. K. 
Published: July 2007

AbstractIt is argued that three‐body interactions have to be introduced even to understand qualitatively the systematics of the measurements of hyperfine fields in Heusler and other related alloys. Formulae for spin polarization including three‐body interaction effects are derived and compared with the Ruderman‐Kittel‐Kasuya‐Yosida theory. As a special case we obtain the results of Blandin and Campbell. We conclude that for any meaningful quantitative comparison with experiments one should include both the three‐body effects and the effects discussed by Blandin and Campbell.
Free‐Carrier Generation via Exciton‐Phonon and Exciton‐Impurity Interaction in Ge Crystals
Authors: Novikov B. V. , Sokolov N. S. , Gastev S. V. 
Published: July 2007

AbstractThe dependence of free electron and hole concentrations on the incident photon energy near the indirect absorption edge in Ge crystals has been investigated by cyclotron resonance at T = 1.8 K. It is shown that such measurements give the possibility to determine the dominant mechanisms of free carrier generation via exciton‐phonon and exciton‐impurity interaction. It is found that in pure crystals free carriers are mainly generated as a result of exciton‐long‐wavelength acoustical phonon interaction. In doped crystals the free carriers are generated due to the interaction of excitons with ionized impurities.
Interaction between Excitons and Radiation‐Induced Radicals in Naphthalene Single Crystals
Authors: Chong T. , Itoh N. 
Published: July 2007

AbstractCorrelation between the fluorescence of a radiation‐induced radical and the quenching of the prompt and delayed fluorescence by the radicals has been studied in naphthalene single crystals. It is found that the fluoresceme of the I‐hydronaphthyl radical is induced by energy transfer from both the singlet and triplet excitons. The interaction rate constant ks between the singlet exciton and the radical is obtained as 6 × 10−9 and 8 × 10−9cm3 s−1 at 290 and 80 K, respectively. Quenching of the delayed fluorescence by the radical is explained by reaction kinetics which involves not only the triplet‐triplet annihilation and a direct collision of a triplet exciton with the radical but also a collision of a triplet‐radical complex or the radical at the excited state with another triplet exciton. The interaction rate constant kT between the triplet exciton and the radicals is obtained as 2 × 10−11 and 3 × 10−11 cm3 s−1 at 290 and 80 K, respectively. It is concluded that the interaction rate constant γ between the triplet exciton and the triplet‐radical complexes or the radical at the excited state is larger than kT which is larger than the rate constant γ for the triplet‐triplet annihilation. It is also shown that the temperature dependences of γ and kT are parallel.
Crystal–Impurity Energy Transport by Molecular Excitons in the Wave‐Like Limit: II. Diffusion in Crystals
Authors: Markvart T. 
Published: July 2007

AbstractThe effect of exciton transport by diffusion on the crystal‐impurity energy transfer is investigated. It is shown that the exciton is likely to be captured by the impurity only if its distance from it is of the order of the exciton mean free path or smaller. On the basis of this argument a modified diffusion equation is developed to account for the exciton motion towards an impurity prior to capture. The equation is solved approximately in the limit of low impurity concentrations.
Exciton Dynamics Study by Magnetic Resonance in TCNQ− · NH
Authors: Alizon J. , Bertret G. , Blanc J. P. , Gallice J. , Robert H. 
Published: July 2007

AbstractThe tetracyanoquinodimethan salt TCNQ− NH belongs to the low conductivity class. It is a simple salt, the two partly deuterated salts TCNQ− · ND and TCNQD · NH can be easily prepared. A substantial amount of information has been gathered concerning the magnetic resonance of these salts: electron spin resonance, dynamic nuclear polarization, and spin‐lattice relaxation. Thus it was possible to study the relaxation mechanisms in this particular case. The experimental results can be interpreted, above the transition temperature, in terms of the model of Frenkel spin excitons; this model introduced by Soos is in good agreement with paramagnetic susceptibility measurements. It is shown that the excitons are localized in the TCNQ chains and have the dynamics of a one dimensional triplet exciton system.
Thickness Dependence of Localized States in a Thin Film with Internal Layer Defect
Authors: Duda A. , Maciejewski W. 
Published: July 2007

AbstractThe thickness effect in the spin‐wave spectrum of a thin film withone internal layer defect is studied. The behaviour of the localized modes and their generation conditions under variation of the film thickness are described by strictly derived analytic formulac. The shape of the thickness effect is related to the pinning situations of the surface spins.
XPS Investigations for the Purpose of the Research of Positron Annihilation Effects in BixSb1−x Alloys Concerning Band Structure Modifications
Authors: Wagner N. , Brümmer O. 
Published: July 2007

AbstractThe reasons for the experimentally definable differences in the decay rate of thermalized positrons in BixSb1−x alloys with different compositions can be investigated with the help of the results of X‐ray photoemission spectroscopy. It is shown that the annihilation rates are influenced by the modification of the valence band properties in the region of p‐like states.
The Elementary Interaction between a Crystal Dislocation and the Flux Line Lattice of a Type II Superconductor
Authors: Schneider E. , Kronmüller H. 
Published: July 2007

AbstractAnalytical expressions for the interaction force between the flux line lattice (FLL) and parallel crystal dislocations are derived within the framework of the micromagnetic theory of superconductivity in the field range 0.6Hc2 < Hext < Hc2. The interaction force was calculated for the ΔV‐effect which results from the inhomogeneous distribution of the order parameter and of the magnetic induction in the periodic FLL. The force exerted per unit length of the FLL by an edge dislocation depends on the value of the applied external magnetic field Hext, and for niobium is of the order of magnitude 10−4dyn/cm, while it turns out to vanish for the case of a parallel screw dislocation. At the upper critical field Hc2 the pinning force due to one dislocation vanishes for a rigid FLL, however, for the volume pinning force a constant value is obtained.
Theory of Low‐Symmetry Effects in Paramagnetic Resonance
Authors: Grekhov A. M. , Roitsin A. B. 
Published: July 2007

AbstractExpressions for the resonant value of a magnetic field and main characteristics of low symmetry effects have been received for the arbitrary local symmetry of a paramagnetic centre in two extremal cases of weak and strong magnetic fields (in comparison with the zero‐field splitting). All terms of the spin‐Hamiltonian allowed by the symmetry and describing the interaction with the external magnetic field and the internal electrical crystal field have been considered. Results of calculations are compared with experimental data.
Phonon‐Assisted Electroabsorption by Contact Excitons
Authors: Pribram J. K. , Penchina C. M. 
Published: July 2007

AbstractThe imaginary part of the dielectric constant for an indirect‐gap semiconductor in a uniform electric field is calculated in closed form using a one‐dimensional electron‐hole contact interaction model. Results are compared with previous calculations for direct transitions. Typical spectra are illustrated for direct and indirect transitions at various field strengths.
EPR Investigations on the (FeOF5)4− Cluster in KZnF3
Authors: Buzaré J. Y. , Fayet J. C. 
Published: July 2007

AbstractThe X band EPR spectrum of the (FeOF5)4− cluster in KZnF3 single crystals was analysed. We used a computer diagonalization for both the Zeeman interaction and the axial crystal field term and a perturbation treatment for the cubic field term and for the shf interaction. This cluster appears to be well adapted for EPR investigations of the structural properties of fluoperovskites.
Pressure Modulation of Exciton Fission in Tetracene
Authors: Whitten W. B. , Arnold S. 
Published: July 2007

AbstractThe fluorescence quantum efficiency of tetracene crystals is found to increase rapidly with pressure. This behavior is interpreted as a reduction in the singlet exciton fission rate due to an increase in the energy separation between the singlet exciton state and the triplet exciton pair state. A red shift in the energy of the S0 → T1 transition by 15 ± 7 cm−1/kbar is used to explain the experimental results. This shift is discussed in terms of the interactions which control the transition energy.
The Coherent Potential Approximation in the Theory of Paramagnetic Alloys
Authors: Kozarzewski B. , Nowak J. , Zieliński J. 
Published: July 2007

AbstractIt is shown how the coherent potential approximation (CPA) can be extended to describe the properties of paramagnetic alloys. The properties of conduction electrons are discussed. Even at very low concentrations of magnetic impurities, results presented here differ from those of the single impurity approximation. As an example the temperature dependence of the resistivity of alloys in the s–d exchange model is analysed. For T much lower than the Kondo temperature, T2 behaviour of the resistivity is derived, which then goes through a more or less pronounced linear region to logarithmic dependence for temperatures higher than TK.
CPA Treatment of the Hubbard Model with Intra‐Atomic Exchange Interaction
Authors: Mizia J. 
Published: July 2007

AbstractThe Hamiltonian for a completely degenerate d‐band including intra‐atomic Coulomb and exchange interactions is derived and studied using the alloy analogy method. Green's function, the magnetic susceptibility and a criterion for the appearance of ferromagnetism are obtained by this method. The dependence of the magnetization on the exchange constant and on the number of electrons per atom is calculated for strong Coulomb correlation and for the uncorrelated case. It is shown that Coulomb correlation of any strength leads to a decrease of the exchange interaction constant needed to produce ferromagnetism and additionally to a change in the shapes of the magnetic dependences for (and only for) weakly ferromagnetic metals.
Über die Berechnung des elektrostatischen Potentials in Kristallgittern: II. Kubisehe Glitter ‐ Berechnungsmethoden für die Summen σ
Authors: Matthies S. 
Published: July 2007

AbstractEs werden auf der Grundlage einer Berechnungsmethode für das elektrostatische Potential in Kristallgittern, die im ersten Teil dieser Arbeit entwickelt wurde, der Fall kubischer Gitter und Berechnungsmethoden für die Summen σ für nichtkubische Gitter betrachtet. Im kubischen Fall werden die Summen σ für l = 4,6, …, 22 berechnet. Die Effektivität der Berechnungsmethode wird am Beispiel eines Gitters vom NaCl‐Typ gezeigt. Es wurde eine Beziehung zwischen den Summen σ für kleine und größere l gefunden.
Theory of Nondegenerate Two‐Dimensional Electrons Interacting with Phonons in Quantizing Magnetic Fields
Authors: Dykman M. I. 
Published: July 2007

AbstractUnder transverse magnetic fields the two‐dimensional electron energy spectrum transforms into a set of essentially discrete Landau levels. Taking into account the non‐parabolicity of the electron energy dispersion a quantum kinetic equation for the case of inelastic scattering by phonons is obtained. This equation is valid over a wide temperature range and at arbitrary ratios between the non‐equidistance of the Landau levels (which is connected with both the non‐parabolicity and the renormalization of the spectrum due to electron‐phonon interaction) and their widths. The shape of the cyclotron resonance peak is considered in the deformation potential approximation and also in the case of scattering by phonons whose frequency is determined by their two‐dimensional wave vector. In the latter case from the shape of the peak it is possible to obtain the phonon dispersion law.
A New Aspect of Jahn‐Teller Effect in the Low‐Spin Ferrihaemoglobin Azide
Authors: Bhattacharyya B. D. 
Published: July 2007

AbstractConsidering the more general molecular orbital method of Van Vleck, Stevens, and Bose et al. the ESR g‐values and the zero‐phonon line structure are discussed for the singlet‐doublet transition in the low‐spin ferrihaemoglobin azide having a predominant tetragonal axial distortion. The model takes into account the anisotropic covalency and the essential features of the Jahn‐Teller effect. Comparison is made with experimental results. The results of correlation between theoretical and experimental g‐values indicate : (i) there is an appreciable anisotropic covalency overlap of the ligand charges with the charge cloud of the central metal atom; (ii) the coupling between electronic and nuclear motions is moderately strong, and (iii) the g‐anisotropy (gx∼gy) has an oscillatory behavior with the degree of Jahn‐Teller coupling.
Optical Properties of MoRe Alloys
Authors: Bahl S. K. , Drew H. D. 
Published: July 2007

AbstractMeasurements of the reflectivity [R(pure) − R(alloy)] of 3000 Å thick Mo‐Re films for photon energies between 0.54 and 6 eV and Re concentrations around 4 at% are reported. The resistivity of the films is also measured and 2.2 μΩ cm/at% is found for the change in resistivity of the films upon alloying. The frequency dependence of the optical dielectric function, ϵ = ϵ1 + iϵ2, of the pure and alloy films is found from a Kramers‐Kronig analysis of the reflectivity data. The results for the differential optical conductivity ω[ϵ2(alloy) minus;ϵ2(pure)] are discussed in terms of the changes in the electronic structure of Mo upon alloying with Re. It is concluded that the rigid band model is inapplicable in this case. The results of the optical data and the resistivity are consistent with the formation of localized Re d‐levels 0.8 eV below the Fermi level where pure Mo has a low density of electronic states. However, this interpretation is not unique and further studies are suggested.
Zeeman Effect of Bound Exciton Complexes in ZnO
Authors: Loose P. , Rosenzweig M. , Wöhlecke M. 
Published: July 2007

AbstractEmission and absorption spectra are measured of several ZnO‐crystals in the region of bound‐exciton complexes near the band gap. From Zeeman‐effect studies up to 8 T at several angles between the c‐axis of the crystal and the magnetic field most of the observed spectral lines are identified. The electron g‐factor is found to be ge = 1.8, if the exciton is formed with a hole from the A‐band, and ge = 2.1, if the exciton is formed with a hole from the B‐band. The mass of the B‐hole seems to be nearly equal to the mass of the A‐hole.
Electronic Properties and Relaxation Processes of Fe2+ in Iron Bisacetylacetonate Dihydrate from Mössbauer Spectroscopy
Authors: Mathieu J. P. , Chappert J. 
Published: July 2007

Abstract57Fe Mössbauer spectra of Fe(acetylacetonate)2 · 2 H2O have been measured between 300 and 4.2 K and in external magnetic fields up to 60 kOe. Strong texture effects due to the shape of the microcrystals are observed. An analysis of the spectra shows that the Fe2+ ion is in a high‐spin state. Under the action of spin‐orbit coupling and external magnetic fields the ground state of the Fe2+ ion is a spin‐doublet somewhat split by about 1 cm−1. A magnetically induced reduction of the relaxation rate is observed.
The Self‐Damping of RKKY Interaction in Dilute Magnetic Alloys
Authors: Takanaka K. , Yamamoto B. 
Published: July 2007

AbstractAn analytical expression for the self‐damping of RKKY interaction is obtained using the temperature Green's function. This expression gives the expected damping factor, exp (– R/l), where l and R are the mean free path of an electron and the distance between two magnetic impurities, respectively. Some qualitative features of the BKKY interaction predicted by this expression are in good agreement with numerical results obtained by de Gennes.
Transport in Microscopically Inhomogeneous Materials
Authors: Pike G. E. , Seager C. H. 
Published: July 2007

AbstractThe solutions are discussed to several types of site and bond conductance networks. The site models include those which are used to describe diffusion in Si–Ge alloys and conductivity in such systems as metal‐ammonia solutions and sodium‐tungsten bronzes. The bond model discussed here is shown to provide a reasonable explanation of data obtained from He diffusion studies in SiO2. Several approaches to solving these conductance models are discussed including numerical solutions, percolation models, and effective medium theories. It is shown, that an extension of the site effective medium theory of Watson and Leath provides a good fit to the numerical data available on the site networks considered.
Thermodynamical Properties of Isotropic Ferromagnets with Biquadratic Interactions
Authors: Biegala L. 
Published: July 2007

AbstractThe thermodynamical properties of a S = 1 system described by \documentclass{article}\pagestyle{empty}\begin{document}$ H = - \frac{1}{2}I\mathop \Sigma \limits_{i,j} {\rm S}_i {\rm S}_j - \frac{1}{2}K\mathop \Sigma \limits_{i,j} ({\rm S}_i {\rm S}_i)^2 $\end{document} are investigated by means of the Green functions method. Using the RPA decoupling the temperature dependence of the two order parameters are determined in the low‐temperature region and in the neighbourhood of the transition temperatures. The value of K for the tricritical point is found. The possibility of the first order transition from the quadrupolar to the disordered phase is analysed.
Correlation Factors and Isotope Effect for Self‐Diffusion by Mono‐ and Divacancies in H.C.P. Crystals
Authors: Steiner E. , Mehrer H. , Seeger A. 
Published: July 2007

AbstractThe tensor components of the Bardeen‐Herring correlation factor for a divacancy mechanism of self‐diffusion in an h.c.p. crystal are calculated and compared with Mullen's results on the monovacancy mechanism. The relationship between the correlation factors and the isotope effect parameters is discussed, in the monovacancy case making use of the work of Batra. For monovacancy diffusion parallel to the c‐direction the correlation factor provides an upper limit for the isotope effect parameter, whereas for diffusion perpendicular to the c‐axis the isotope effect parameter can be slightly larger than the correlation factor. For the divacancy case it is demonstrated analytically that the correlation factor parallel to the c‐axis provides an upper limit for the isotope effect parameter in this direction. Numerical calculations show that the upper limit of the isotope effect parameter perpendicular to the c‐axis exceeds the correlation factor at most by a few per cent.
Optical Relaxation Time and Effective Mass in Noble Metal Alloys
Authors: Brauwers M. , Brouers F. 
Published: July 2007

AbstractThe CPA expressions of optical relaxation time and effective mass in a two s–d hybridized band noble metal alloy model are investigated. This model considers the effect of the d‐diagonal and off‐diagonal and s‐diagonal disorders; comparison is made with experimental data on AuxAg1−x.
Measurement of Mössbauer Diffusion Broadening in α‐Iron Stabilized with Vanadium
Authors: Lindsey R. 
Published: July 2007

AbstractThe diffusion of iron 57 in α‐iron stabilized by small amounts of vanadium is studied by means of the Mössbauer effect. The Mössbauer line broadening is found to be proportional to the diffusivity. The broadening observed is found to be about half that predicted in uncorrelated sudden jump model of Sing wi and Sjölander. The observed lineshapes are Lorentzian to within experimental errors. The data indicates that the recoil‐free fraction falls off more rapidly than predicted by a Debye model at temperatures where diffusion broadening is observed. An effective Mossbauer characteristic temperature of (299 ± 13) °C represents the data taken between the Curie temperature and the onset region of diffusion broadening.
Magnetic Aftereffect Phenomena in Cobalt between 4.2 and 20 K after Low‐Temperature Electron Irradiation
Authors: Dander W. , Kronmüller H. , Schaefer H. E. 
Published: July 2007

AbstractIn Co single crystals irradiated by 3 MeV electrons at 4.2 K a complex magnetic aftereffect (MAE) spectrum between 4 and 350 K has been observed. This paper deals with the low‐temperature MAE processes at 5, 9, and 17 K as well as with their annealing after irradiation to different doses. Taking into consideration simultaneous measurements of the resistivity annealing and the initial susceptibility, a model will be suggested which attributes the 9K‐MAE and its complex annealing behaviour to the rotation and transformation of interstitials which may migrate freely at 65 K.
Second‐Order Raman Spectra of RbCl, RbBr, and RbI Crystals
Authors: Goel C. M. , Dayal B. 
Published: July 2007

AbstractThe polarized second order Raman spectra of three rubidium halide crystals, namely RbCl, RbBr, and RbI are computed on the basis of the theory proposed by Born and Brad‐burn, taking into account first as well as second neighbour polarizability coefficients. The three‐body force shell model is employed to determine the phonon frequencies, the phonon eigenvectors, and the polarizability tensor. The polarizability coefficients are assumed to be adjustable parameters. It is found that in addition to all the first neighbour coefficients, only eight second neighbour coefficients are sufficient to obtain good agreement between the experimental and the theoretical spectra.