bluuebunny/crossref_metadata_2025 huggingface dataset:
EPR of Mn2+‐Doped Tutton Salts. Role of Hydrogen Bonding
Authors: Pandey R. C. , Chaudhry A. K. , Shukla S. R. , Pandey S. D.
Published: July 2007

The work deals with electron paramagnetic resonance of Mn2+‐doped zinc potassium selenate hexahydrate and zinc cobalt selenate hexahydrate Tutton salt single crystals. The different field parameters for the two hosts are evaluated from the observed z‐ and x‐axes spectra. The D parameters for the two hosts are compared with the corresponding reported values for hexahydrate. This parameter shows a systematic variation with the change in radii of the M′ ion in the series of salts ZnM′2(SeO4)2. 6H2O with M′ as K, Rb, and Cs. The case of M′ as NH4, however, does not show such a systematics. Similar behaviour is found for two other such series of Tutton salts, as well. Further it is found that D is, in general, negative for K, Rb, and Cs Tutton salts but is positive for NH4 Tutton salts. This unusual behavior of NH4 Tutton salts is attributed to two types of hydrogen bondings existing in such Tutton salts, in contrast to the only one type linking the H2O groups to the sulphate groups in all other Tutton salts. An attempt is also made to explain the unusual reported negative value of D in ammonium‐iron, ammonium‐cadmium, and ammonium‐nickel Tutton salts.
Surface Spin Waves in Semi‐Infinite Antiferromagnetic and Ferrimagnetic Semiconductors in the Narrow‐Band Limit
Authors: Shen Wen‐Zhong , Li Zhen‐Ya
Published: July 2007

Surface spin waves are investigated in semi‐infinite s‐d (or s‐f) interaction antiferromagntic and ferrimagnetic semiconductors in the narrow‐band limit by use of combined Green's function theory with the transfer‐matrix method. The influence of s‐d (or s‐f) interaction on surface spin‐wave spectra is discussed.
No Longer Transcendental Equations in the Homogeneous Mean‐Field Theory of Ferromagnets
Authors: Millev Y. , Fähnle M.
Published: July 2007

The transcendental equation for the determination of the magnetization within the mean‐field approximation is reduced to the problem of solving an explicit polynomial equation of degree 2S where S is the spin of the localized magnetic moments. Various possibilities to achieve this reduction are pointed out and the physically most tractable variant is singled out. It is demonstrated that the solution of the obtained polynomial equation is equivalent to finding the inverse of the Brillouin function explicitly.
Stochastic Processes and Asymmetry of Raman Scattering at the Surface of Opaque Crystals
Authors: Semjonow A. Je. , Holz L. , Lau A. , Richter W.
Published: July 2007

First experimental results are presented about a new type of asymmetry of the spontaneous Raman scattering (ASRS) in crystals (Si after UV irradiation), where not only the probabilities of light scattering are different for the scattering to the right and to the left directions, but also the phonon frequencies and halfwidths are different. The experimentally observed features of ASRS in crystals are explained theoretically by a chaos model of nonlinear optics (a chaotic Raman attractor). The interactions between Stokes, anti‐Stokes, and pump laser waves cause the new type of ASRS in crystals. It is shown that Stokes and anti‐Stokes modes may exhibit the redistribution of phonon intensities, different phonon frequencies, and linewidths.
Temperature Dependent Energy Shifts in the Resonance Absorption and Resonance Fluorescence Scattering of Mössbauer γ‐Quanta in FeS2
Authors: Jex H. , Hillmann H. , Müllner M.
Published: July 2007

The relativistic Doppler effect of Mössbauer γ‐quanta from a 57Co source is investigated in the resonance absorption of FeS2 powder and in the resonance scattering from the (200) reflection of FeS2 single crystals in the temperature range 298 K ≦ T ≦ 598 K. The shift of resonances is d ln ω/dT = −(2.58 ± 0.07) × 10−15 K−1, while the quadrupole splitting dEQ = (633 ± 9) μm/s is temperature independent. Single crystal data exhibit an unexpected additional broadening of one quadrupole resonance, which originates in an interference of nuclear resonance and electronic Rayleigh scattering.
Effect of Isotope Substitution on Thermal Expansion of LiH Crystal
Authors: Tyutyunnik V. I.
Published: July 2007

The isotope effect on the lattice parameter and the coefficient of thermal expansion of the LiH crystal is investigated by means of rigid‐ion model. It is demonstrated that the differences in lattice parameters between LiH isotopes can be related directly to changes in the thermal‐expansion coefficient which varies inversely as the cation‐anion reduced mass. These differences should disappear at a temperature of 0 K. For the first time, the thermal‐expansion data are calculated for the six isotopic components 6LiH, 7LiH, 6LiD, 7LiD, 6LiT, and 7LiT. The lattice parameters of LiH isotopes are also calculated and agree with those observed earlier within the experimental error.
Differential Photoluminescence Excitation Spectroscopy A Novel and Sensitive Tool to Probe Gain and Absorption in Semiconductor Nanostructures
Authors: Bongiovanni G. , Mura A. , Staehli J. L.
Published: July 2007

Differential photoluminescence excitation (DPLE) spectroscopy is shown to be an efficient way to measure gain and absorption spectra of excited semiconductors. Very small excited volumes can be probed, and thus DPLE spectroscopy is ideal to probe nanostructures. This technique is applied to investigate the width of the gap between the second electron and hole subbands of a quantum well versus carrier density, in a sample which contains only a few wells. It is found that the reduction of this gap is a smooth function of the electron–hole pair density, and no drastic change occurs when the second subbands start to be populated.
Surface‐Emitting Laser Logic
Authors: Olbright G. R. , Jewell J. L. , Bryan R. P. , Brennan T. M.
Published: July 2007

In the future optoelectronic integrated circuits (OEICs) are destined to evolve into sophisticated functional circuitry upon which a multiplicity of applications will be based such as: optical communications, optical interconnects, optical computing, optical memory, laser printing and scanning, visual displays, pattern recognition, and neural networks. This evolution of OEICs involves the integration of phototransmitters (semiconductor lasers and light‐emitting diodes), photoreceivers (photodetectors and phototransistors), spatial‐light modulators transistors (bipolar and field‐effect), diodes, resistors and capacitors, and micro‐optic components (e.g. micro lenses). Our efforts to date and future directions are described which are concentrated on the integration of vertical‐cavity surface‐emitting laser diodes (VCSELs) with transistors, photoreceivers and micro‐optic components. VCSELs, which may be patterned in high densities (over a million in a cm2) and emit light perpendicular to the plane of the substrate, have an ideal light‐emitting geometry for the above‐mentioned applications and for integration with micro‐optic components. Our effects to develop monolithic surface‐Emitting Laser Logic devices are described which are referred to as CELLs consisting of phototransistors, current controlled bipolar transistors, and voltage‐controlled field‐effect transistors integrated with a VCSEL to form optically and electrically addressable photonic switching devices having high contrast. Included are reports of recent progress in decreasing VCSEL series resistance and therefore operating voltage, and an optically‐pumped visible‐emitting (657 nm) VCSEL. Also discussed are the integration of micro‐optics with VCSELs. Finally combinations of OEIC components and subassemblies and their applications to several of the above‐mentioned photonic switching applications are described.
Synthesis and Characterization of the Layered Compounds in the ZnIn2S4–ZnIn2Se4 System
Authors: Razzetti C. , Attolini G. , Bini S. , Lottici P. P.
Published: July 2007

By the chemical vapour transport technique some compositions in the ZnIn2S4–ZnIn2Se4 system are synthesized. The layered reaction products obtained are characterized by X‐ray diffraction, atomic absorption spectroscopy, and Raman scattering. According to the crossed characterization the reaction products have a composition strongly different from the loaded charge, and their structure is related to that of Zn2In2S5 rather than to that of ZnIn2S4. According to the characterization, the structure shows a large degree of disorder both in the anion and the cation sublattices which is mirrored by the Raman spectra apart from very narrow Raman lines which are observed at very low frequencies.
Influence of Sample Temperature on the Process of Hot Spot Formation and Degradation after Powerful Laser Pumping
Authors: Pronin D. A.
Published: July 2007

The degradation of a hot spot obtained near one of the surface of a thin crystal plate of anthracene at helium temperatures is investigated. The experimental results are discussed in terms of the local thermal conductivity with both specific heat and thermal conductivity as well‐known function of temperature. A good agreement between experimental results and model calculations is achieved. Analyzing the results of calculations a conclusion is drawn on the strong influence of sample temperature on the process of hot spot formation immediately after laser pumping. The role of the sample defectiveness is also discussed. The solution of the non‐linear thermal conductivity equation used to describe experimental results is analyzed. It was found that initial conditions strongly affect the time evolution of the hot spot width.
Lattice Dynamics of Acetylene
Authors: Binbrek O. S. , Anderson A.
Published: July 2007

A simple force constant model is described and applied to the vibrations of crystalline acetylene, C2H2 and C2D2, in its low temperature orthorhombic phase. The model uses ten (six intermolecular and four intramolecular) adjustable parameters to calculate the frequencies of seven lattice modes and fourteen internal mode components, and good agreement with spectroscopic data is obtained. Intermolecular force constants decrease sharply with increasing sepration and are well represented by exponential functions. Intramolecular force constants show only minor changes from their gas phase values.
Van der Waals Forces between Conducting Films
Authors: Gerlach E.
Published: July 2007

The van der Waals force between two conducting films embedded in a dielectric medium is calculated. Spatial dispersion may lead to a drastic modification of the Drude model over a wide range of separation. The singularity of the force at small separations disappears.
Non‐Coherent Light Reflection from Photoelastic Media
Authors: Grechko L. G. , Motrich V. V. , Ogenko V. N. , Semchuk A. Yu.
Published: July 2007

The present study is concerned with non‐coherent light scattering due to interaction of an incident electromagnetic wave with fluctuations of Rayleigh surface waves at the isotropic photoelastic medium boundary. Two mechanisms of the interaction of an electromagnetic wave with Rayleigh surface waves are considered: interaction of electromagnetic wave and surface wave a) by means of the inhomogeneity of the dielectric constant and b) by means of the photoelastic mechanism. A general expression for the coefficient of non‐coherent reflection is obtained.
Modelling of Thulium Ion Luminescence in Zinc Sulphide
Authors: Rodionov V. E. , Rakhlin M. Ya. , Zolotovskii A. A.
Published: July 2007

The modelling of luminescence of the Tm3+ ion in zinc sulphide for TmS4, TmS3Vs, TmS3Cl, TmS3F, TmS3Br, TmS2F2, TmSF3, TmVsF3 clusters is considered by the quantum‐chemical MO AOLC (molecular orbitals of atomic orbital linear combinations) method within the limits of the Routan approximation. The intensities of luminescent transitions are calculated. The dependence of intensities and the ratio of intensities of blue and red emissions of a cluster on its composition, symmetry, and geometry are analysed.
On the density of electron states and magnetization of the crystalline narrow band sd model
Authors: Ponedilok G. V. , Shabat I. E.
Published: July 2007

The model which describes exchange interaction of localized magnetic moments with itinerant conduction electrons and Hubbard correlations is considered. The set of equations necessary to calculate self‐consistently the density of electron states (DOS) for the narrow band sd model is obtained. The numerical analysis of the zone electron magnetization for the rectangular model zone is given.
Finite lifetime effects in the coherent exciton transfer
Authors: Barvík I. , Heřman P.
Published: July 2007

Memory functions entering the generalized master equations are calculated for trimer, with the sink in the center. The whole dynamics of the system – coherent transfer, capture of the excitation by the sink, and finite lifetime effects in the host – are taken into account. The simple example of the trimer is chosen (method and results being simply extendable to more complex systems) to present the analytical solution, which is obtainable also by the use of the program package Mathematica for symbolic computing.
General dispersion equations for diluted magnetic semiconductor superlattices
Authors: Shen Wen‐Zhong , Li Zhen‐Ya
Published: July 2007

On the basis of the magnetostatic theory, we derive the general dispersion equations for diluted magnetic semiconductor (DMS) superlattices. Both bulk and surface dispersion relations are obtained in the superlattices with the elementary unit consisting of l different DMS layers.
Phenomenological description of magnetic relaxation in magnetic crystals with induced anisotropy
Authors: Lyakhimets S. N.
Published: July 2007

A phenomenologic description of a magnetic dissipation in crystalline magnets with induced magnetic anisotropy is suggested. The components of the second‐order tensor describing the induced anisotropy are taken as thermodynamic variables and the nonequilibrium linear Onsager thermodynamics is formulated for them. Such an approach comprehends all symmetry aspects of the relaxation problem. With the help of the dissipation function the relaxation parameters and their angular dependences are calculated for spin waves and moving domain walls.
An electron paramagnetic resonance study of Fe3+ ions doped in langbeinites
Authors: Böttjer T. , Stockhausen M.
Published: July 2007

Powder and single crystal X‐band EPR spectra are measured of the cubic (high temperature) phase of eleven langbeinites, A2+B (SO4)3, doped with Fe3+. One center of axial symmetry is observed, the ZFS parameter B of which is discussed in comparison with corresponding results on manganese‐doped langbeinites. Very probably Fe3+ forms a substitutional center in the more spacious of the two non‐equivalent B sites, which leads to local relaxation depending on ionic radii. Charge compensation by an A site vacancy is likely.
Confinement effects on the LO‐phonons in CdSexS1–x doped glasses
Authors: Bersani D. , Lottici P. P.
Published: July 2007

Raman scattering on commercial filters containing CdSexS1–x microcrystals is reported. The composition x is determined by the difference between CdS‐ and CdSe‐like LO phonon frequencies. A simple phonon confinement model in the microcrystals is suggested to explain the observed red‐shift of the Raman frequencies and the lineshapes.
On Electron Emission from Quantum Wells in Ultrathin Films of Wide‐Gap Semiconductors in Crossed Fields
Authors: Das N. R. , Chakravarti A. N.
Published: July 2007

An attempt is made to investigate the effects of an oriented magnetic field on the field emission from quantum wells in ultrathin films of wide‐gap semiconductors taking n‐type GaAs as an example. The field emission current density is found to increase both with increasing electric field and with increasing film thickness. Furthermore, the emission shows an oscillatory nature with a quantizing magnetic field, its orientation, and the film thickness. At a given value of the magnetic field, the oscillatory nature is most significantly influenced by the effects of size quantization at relatively small values of the film thickness.
Plasmon‐Mediated Pairing Arrangement of the One‐Dimensional Electron System
Authors: Yanetka I.
Published: July 2007

The possibility of various types of pairing arrangements is examined in a one‐dimensional system in which the effective interparticle interaction of Coulomb type is evaluated in the plasmon‐pole approximation. The insulating state arising from the particle‐hole pairing arrangement appears to dominate strongly over the superconductive effects. The dependence of the transition temperature on the band width is calculated for a set of typical parameter values with the help of the derived integral equation which formally coincides with the well‐known equation of the theory of superconductivity.
Finite Temperature Valence Transition in Mixed Valence Systems
Authors: Ghosh N. K. , Sarkar R. L.
Published: July 2007

The valence transition at finite temperature in mixed valence (MV) systems is investigated using the extended Falicov‐Kimball (F‐K) model with Coulomb f–f and the electron‐phonon (EP) interactions. The role of different interactions and the influence of temperature on the valence transition are studied. It is found that the lowering of temperature favours the transition. The results are compared with existing experimental findings.
Relativistic Impacts on Electrical Resistance of a One‐Dimensional Finite Crystal
Authors: Roy C. L. , Basu Chandan
Published: July 2007

A relativistic study of electrical resistance in a one‐dimensional finite crystal with rectangular barrier type of atomic potentials is reported. The procedure applied is based on an appropriate relativistic generalisation of Landauer's non‐relativistic treatment of electrical resistance for a finite number of potential barriers. The relativistic impact on electrical resistance in our model is studied only in regard to the velocity of electrons. The quantitative extent of such an impact is critically discussed.
Calculation of Electrical Resistivity of Liquid Transition Metals
Authors: Ononiwu J. S.
Published: July 2007

The transport properties of liquid transition metals are discussed on the basis of Ziman's theory as generalized by Evans, Greenwood, and Lloyd. The effect of d‐band resonance in transition metals is simulated in the nearly‐free electron approximation where the ordinary (V‐matrix) pseudopotential form factor is replaced by the T‐matrix form factor in the transport integral. The T‐matrix form factor is derived in a closed form from the transition‐metal model potential V‐matrix form factor by solving the appropriate T‐matrix integral equation. The solution takes into account the deviation of the electron density of states at the Fermi level from the free‐electron value, through the ratio g = N(EF)/N0(EF), which is estimated from experimental heat capacity and McMillian's electron phonon renormalization constant in group‐B transition metals to have a mean value of order g = 2 for liquied transition metals. Based on this estimate of g and Mott's form of Ziman's formula, the electrical resistivity is calculated for all group‐B liquid transition metals using the parameters of the transition‐metal model potential obtained by Animalu in 1973. The results are in reasonable agreement with the experiment.
Magnon‐Induced O‐Hole Interaction in a pdtJ Model for CuO2 Superconductors
Authors: Bryja L. , Kolley E. , Kolley W.
Published: July 2007

An effective model for O‐hole quasiparticles is derived from the t˜pp–Jpd–Jdd–Jpp (or pdtJ) model stemming from the minimal version of the Emery model. The underlying procedure involves an antiferromagnetic (AF) Holstein‐Primakoff transformation, a Schrieffer‐Wolff transformation, and an AF Bogolyubov transformation. The investigation of the diagonal part of the effective vertex shows the dominance of the AF magnon‐mediated repulsion over the a priori attraction between O‐hole quasiparticles along the boundaries of the magnetic Brillouin zone. In view of the pairing, formal similarities to the spin‐bag mechanism are pointed out.
Specific Features of the Defect Formation in LiF Crystals as a Result of Implantation of Li+ and F+ Ions
Authors: Alekseeva L. I. , Titov Yu. M. , Urusovskaya A. A. , Knab G. G. , Guseva M. I. , Gordeeva G. V.
Published: July 2007

The results of an investigation of the mechanical, electrical, and optical properties in the near‐surface layer of LiF crystals irradiated with Li+ and F+ ions (energy 80 keV, fluence up to 1017 cm−2) are presented. The hardening in the layer, the thickness of which is by an order of magnitude larger than the ion penetration depth, as well as a significant difference in conductivity change are revealed. The conductivity change is explained in the case of F+ implantation by a combination of cation vacancies with hole centers and in the case of Li+ implantation by the appearance of an electron component in conductivity with an activation energy of 0.36 eV. By optical measurements the temperature change of the position and half‐width of the colloidal absorption band is observed. The latter one is connected with electron‐phonon interaction in Li colloidal particles. It is found also that the colloidal band can be separated into three elemental bands, the shape of which is nearly Gaussian in wavelength coordinates due to the statistical particle‐size distribution.
Impact Parameter Dependence of the Electronic Stopping Power for Channeled Ions
Authors: Nakagawa S. T.
Published: July 2007

In order to examine the dependence of the electronic stopping power (dE/dx) on the impact parameter p, the energy dissipation of axially channeled ions with curved trajectories is studied theoretically by means of a cluster model. dE/dx is accounted in the framework of nonlinear molecular dynamics (MD) coupled with the local density approach (LDA) based on the Lindhard‐Winther (LW) theory. A correction factor of 2 is introduced to compensate the lower dE/dx, especially for low‐energy ions. B ions are implanted into Si 〈100〉 and 〈110〉 at incident energy in the region 10 keV ≦ E0 ≦ 10 MeV. Results are the following. Firstly two kinds of solid‐state effects on the p‐dependence of dE/dx are found at high and low E0, respectively. At high E0 (> 100 keV) the core electrons reveal quite different profiles of dE/dx versus p than valence ones, and at low E0 (< 100 keV) the topological difference in the electron distribution among axial channels appears in those profiles, which cannot be explained by means of collisions with single atom. Secondly, the p‐dependence of dE/dx is intended to adapt the simple form dE(p)/dx = A exp (‐sp/a). The factor s due to core electrons increases distinctly with E0, while that due to valence electrons is almost invariant, smaller than 0.3.
Transport Properties in Liquid Metal Binary Alloys
Authors: Jain K. C. , Gupta N. , Saxena N. S.
Published: July 2007

A theoretical study of the transport properties viz., the shear and bulk viscosity, thermal conductivity, and surface tension in some liquid metal binary alloys at different concentrations is presented. The results obtained for these transport properties in liquid NaK, NaCs, KCs, KPb, NaPb, NaSn metal alloys employing the model given by Davis et al. are in a good agreement with the results calculated using other theoretical approaches.
Phonon Properties of a Three‐Component Fibonacci Chain
Authors: Hu A. , Yang F. , Jiang S. S.
Published: July 2007

Through the transfer matrix method the phonon properties of a three‐component Fibonacci chain are studied. The eigenfrequencies and the eigenstates are computed using a finite quasi‐periodic chain and periodic boundary conditions. Computed results show that not only the scaling index of the phonon spectrum, but also the eigenstates depend on the frequency ω.
Deformation Potentials in AIIBIVC2V Ternary Chalcopyrite Semiconductors
Authors: Rincón C. , Fernández B. J.
Published: July 2007

Deformation potentials of valence and conduction bands in AIIBIVC2V chalcopyrite semiconductors are calculated from the variation of the energy gap with temperature and pressure. From a comparison with their binary analogues AIIIBV it is found that values of deformation potentials in these compounds are considerably higher than in the binaries which could explain their lower carrier mobility.
Phase Diagram of a Quantum Transverse Spin‐1 Ising Model with Random Fields
Authors: Ma Y. Q. , Ma Y. G. , Gong C. D.
Published: July 2007

The quantum spin‐1 Ising system with random fields is investigated by combining the pair approximation with the discretized path‐integral representation. An analytical expression for the second‐order phase transition is derived for all symmetrical probability distributions of random fields, and phase diagrams for Gaussian and bimodal random fields are obtained numerically.
Stability and Thermodynamical Properties of Liquid NaSn Alloys
Authors: Michael Helen M. , Sahay B. B.
Published: July 2007

Stability and the alloying behaviour of liquid NaSn alloys are investigated with the presumption that a chemical complex of the form Na4Sn or Na3Sn exists in liquid NaSn alloys and this is used to determine their free energy of mixing and also entropy of mixing. The computed values of the free energy of mixing and entropy of mixing as a function of concentration are in good agreement with the experimental results. It can, therfore, be inferred that the thermodynamical behaviour of liquid NaSn alloys may be explained, even with the presumption of only one type of chemical complex instead of two as assumed by Tamaki et al. and Hoshino [1, 2].
Effect of the Short‐Range Order in Binary Alloys
Authors: Jezierski A.
Published: July 2007

The influence of the chemical short‐range order effect on the electronic density of states in binary alloys is studied. The electronic structure is calculated by the TB LMTO CPA method. Increasing density of states at the Fermi level N(EF) is observed with increasing short‐range order parameter in Pt0.75Mn0.25 and Hf0.25Rh0.75 alloys.
Anomalous Hall Effect in Cerium Based Kondo Systems
Authors: Prabhu R. B. , Barbosa A. F.
Published: July 2007

A self‐consistent perburbation theory to calculate magnetoresistivity, susceptibility, and the Hall constant for the crystal field split cerium based systems is employed. In this theory, excitonic and other correlations are included self‐consistently. The resulting non‐linear integral equations for the conduction electron scattering amplitude are solved perturbatively retaining terms up to fourth order in V, the Anderson mixing interaction. We calculate the Hall constant as a function of temperature for various positions of the f‐level. We compare our results with the experimental data on cerium based compounds.
Transmission and Conversion Electron Mössbauer Investigation of Fe81B13.5Si3.5C2 Glass under RF Thermal Treatment
Authors: Bibicu I. , Rogalski M. S. , Nicolescu G.
Published: July 2007

Pulsed 54.8 MHz rf annealing of Fe81B13.5Si3.5C2 glass induces – before any crystallization can be detected by X‐ray diffraction – different short‐range ordering effects reflected in the simultaneous recording of conversion electron (CEM) and transmission (TM) Mössbauer spectra. A quadrupole interaction analysis reveals an almost identical threshold energy for the bulk stress relief and for the chemical short‐range order growth evidenced in CEM spectra, attributed to different strength and distribution of the atomic bonding.
Characterization of the Crystal Quality of Calcites by Electron Paramagnetic Resonance
Authors: Vassilikou‐Dova A. B.
Published: July 2007

The linewidths Bpp and anisotropies in the electron paramagnetic resonance spectra of Mn2+ impurities are measured in calcite single crystals and used for the determination of the origin of line broadening. Two different mechanisms of broadening, structural and chemical, are distinguished. From the differing angular dependences of the observed linewidths, large differences in the crystal quality are inferred. The differences in quality are also apparent in the EPR spectra of powder calcites, but no information about the mechanisms can be obtained.
L2 and L3 X‐Ray Absorption Edge in Fluoride Glasses
Authors: Wang Wen‐Cai , Chen Yu , Hu Tian‐Dou
Published: July 2007

The Ba and Nd L2,3 X‐ray absorption spectra in ZrF4BaF2NdF3 and some ZrF4BaF2 binary glasses are studied. It is observed that the intensities of the white lines (WLs) in Nd and/or Ba L2,3 edges from these materials differ from those of their fluorides. Besides, the intensity ratios of the WLs in Ba and Nd L2,3 edges, L3/L2 deviate from the statistical value. These ratios for the studied glasses are also not the same as those from the corresponding fluorides. However, these changes of both the WL intensities and the ratios L3/L2 in Ba L2,3 edges differ from those in Nd L2,3 edges. These differences are discussed and attributed to the differing interaction between Ba or Nd and F in the glasses.
Phonon Frequencies in Metallic Glasses
Authors: Agarwal P. C. , Kachhava C. M.
Published: July 2007

The Ashcroft empty core model potential is used to derive the effective interatomic potential, Veff(r), and the pair correlation function, g(r), of metallic glasses through the pseudopotential approach. The only parameter rc (core radius) is chosen to make the calculated g(r) as close as possible with available experimental data. Veff(r) alongwith g(r) of the glass is used to evaluate longitudinal and transverse phonon frequencies by the use of the Takeno and Goda equations. The formulation reproduces the main characteristics of the dispersion curves obtained by computer simulation techniques.
On a Simplified Analysis of the Effective Electron Mass in Ultrathin Films of Nonparabolic Semiconductors in the Presence of a Parallel Magnetic Field
Authors: Ghatak K. P. , Bhattacharyya D.
Published: July 2007

An attempt is made to study the effective electron mass at the Fermi level in ultrathin films of nonparabolic semiconductors in the presence of a parallel magnetic field on the basis of a newly derived electron dispersion law. It is found, taking n‐Hg1−xCdxTe and In1−xGaxAsxP1−y lattice matched to InP as examples, that the effective Fermi level mass depends on the subband index in addition to the Fermi energy due to the presence of the magnetic field. The effective masses corresponding to different subbands increase with increasing surface electron concentration and decreasing film thickness. Besides, thc numerical values of the masses in quaternary alloys are smaller than those for ternary semiconductors. In addition, the corresponding well‐known results of ultrathin films of nonparabolic Semiconductors in the absence of the magnetic field are also obtained as special cases of our generalized formulation under certain limiting conditions.
The Temperature Dependence of the Energy Gap in Cd0.22, Hg0.78Te. II. Hall Effect Measurements
Authors: Hlídek P. , Grill R. , Höschl P. , Moravec P. , Zvára M.
Published: July 2007

Hall effect data evaluated with various assumptions regarding the energy band parameters are compared with the results of optical measurements. The energy gap Eg, of an ideal crystal described by the Kane band model should be distinguished from the energy difference ET between conduction and valence band tail states which contribute also to the carrier transport. The temperature coefficient of Eg(T) is proposed to be higher than that used in the well‐known Hansen‐Schmit‐Casselman relation, while ET, versus temperature varies more slowly as a consequence of a broadening of the band tails with increasing temperature.
Magnetic Field Induced Triplet Exciton Polariton in CuCl
Authors: Ando T. , Hasuo M. , Nagasawa N.
Published: July 2007

The integrated optical absorption I (B) due to the Z3‐triplet exciton in CuCl is measured at 4.2 K as a function of an external magnetic field B (O ≦ B ≦ 0.2 T) in Voigt configuration. I (B) shows the characteristic B‐dependence whose behaviour is ranging between quadratic and linear on B. It is found that this B‐dependence of I is caused by the correlation between the B‐dependent singlet‐triplet mixing and the sample‐dependent damping of the Z3‐triplet exciton. The effects of spatial dispersion due to the finite effective mass of the triplet exciton are taken into account assuming Pekar's ABC. The conceptional transition from a classical Lorentz model to the polariton model is demonstrated experimentally. An application to the characterization of the sample is also discussed.
Correlation between X‐Ray Chemical Shift and Partial Charge in Some Cobalt Systems
Authors: Mehta C. P. , Chetal A. R.
Published: July 2007

The chemical shift of the X‐ray K‐absorption edge of cobalt in the systems CoSO4. 2H2O, CoCl2. 6H2O, Co2O3, Co3O4, CoO, CoS, and (NH4)2SO4 · CoSO4 · 6H2O is studied using a 40 cm Cauchois type bent crystal spectrograph of transmission type. On the basis of least‐square regression analysis a cubic relationship between the X‐ray chemical shift and the partial charge on the absorbing ion is suggested. The relation is utilized for estimating the partial charge on the Co ion in the system (NH4)2SO4 · CoSO4 · 6H2O.
Phonon Disperision Curves of Diamond and Silicon within the Quasi‐Ion Model
Authors: Mohaupt M. , Falter C. , Klenner M. , Ludwig W.
Published: July 2007

The phonon dispersion curves for diamond and silicon in the quasi‐ion model are calculated and additionally the effect of anisotropic breathing is studied. Within the rigid quasi‐ion model (RIM) the influence on the phonon dispersion of the localization of the expansion set (Gaussians) for the quasi‐ions is discussed. Furthermore the phonon dispersion curves are investigated taking anisotropic breathing into account. Such an extension allows to influence special modes in the spectrum, in particular the LA‐mode at the L point which is poorly represented in the RIM. Also calculated are phonon‐induced changes of the electronic density in this model for some modes. Anisotropic breathing is associated with a quadrupole contribution to the displacement‐induced change in density in contrast to the RIM where the quadrupole moment vanishes for symmetry reasons.
Optical Absorption, Fluorescence, and Thermally Stimulated Emission on CaF2 : Dy: Pb Single Crystals
Authors: Sastry S. B. S. , Kennedy S. M. Moses
Published: July 2007

The optical absorption (OA) spectra of unirradiated crystals of CaF2 doped with 0.1% Dy (by mol%) and 0.1% Pb, hereafter called crystal I, and doped with 0.2% Dy and 0.1% Pb, called crystal II, indicate the presence of a small amount of dysprosium in their divalent state (Dy2+). There is an increasing absorption towards 6.5 eV. On y‐irradiation the concentration of Dy2+ ions is found to increase. Fluorescence of these crystals shows characteristic Dy3+ emission at 1.62, 1.85, 2.16, and 2.85 eV (4F9/2→6H9/2), 6H11/2, 6H13/2, 6H15/2. In thermoluminescence (TL) glow after γ‐irradiation at room temperature crystal I shows six peaks in the temperature range (300 to 700 K) studied. Dy3+ is found to be the major luminescent centre under all these glow peaks. In addition to the Dy3+ emission bands there are two bands in the UV region at 4.94 and 5.93 eV in TL emission. For higher concentrations of lead the results are somewhat different. Crystal III (with 0.01% Dy and 0.5% Pb) and crystal IV (with 0.02% Dy and 0.5% Pb) show a strong absorption band around 6.4 eV. On irradiation prominent absorption bands are observed around 2.04 and 3.21 eV. These are attributed to an F centre associated with the rare‐earth ion in its divalent state (Dy2+ –F centre complex), akin to the FA centre in alkali halides. It is also found that the lead ions (Pb2+) when excited, transfer their energy to nearby Dy3+ ions, leading to the characteristic emission of Dy3+ ions.
Study of Diffusion on a Deterministic Fractal
Authors: Dasgupta R. , Ballabh T. K. , Tarafdar S.
Published: July 2007

Fractal systems exhibit anomalous diffusion where the mean square distance covered in a random walk (RW) is related to time t as 〈r2〉 ∼ t2/dw with dw ≠ 2. The presence of a bias along any direction in fractal systems gives rise to competing effects ‐ enhanced diffusion as well as trapping at dead ends. A random walk on a Vicsek fractal (VF) is studied. The same exponent dw is obtained from a similar vibrating mass‐spring system. Introducing a bias along the positive Y‐direction in RWs, the competing effects are also observed. Results are compared with another well‐studied deterministic fractal, the Sierpinski gasket (SG).
Investigation of Ballistic Phonon Propagation in Quartz by the Time‐of‐Flight Method
Authors: Sujak‐Cyrul B. , Szczepański J. , Tyc T.
Published: July 2007

The ballistic phonon propagation in α‐quartz is measured in directions z and y, for different bolometer currents, by the time‐of‐flight method. For higher currents on time‐dependent bolometer signal curves more singularities are observed than it was reported earlier. On the basis of calculations the observed singularities are explained as separately detected phonon modes and the increase of their number is connected with a diminution of the bolometer active area by increase of bolometer current for very thin aluminium bolometers.
Superconducting Properties of Y1−xCaxSrBaCu2.9Ga0.1O6+z
Authors: Suryanarayanan R. , Ouhammou L. , Leelaprute S. , Le Nagard N.
Published: July 2007

The lattice parameters and ac susceptibility of Y1−xCaxSrBaCu2.9Ga0.1O6+z (x = 0, 0.05, 0.1, and 0.2) are reported. Tc decreases as a result of (0.1) Ga substitution from 83 to 67.5 K but increases to 79.5 and 80 K for x = 0.1 and 0.2, respectively. The present data in comparison with those on Al and Co which have been shown to occupy chain sites suggest strongly that Ga also preferentially occupies the chain sites.
On the Quasistochastic Behavior of Nonlinear Magnetization Oscillations in Orthorhombic Ferromagnets Induced by a Magnetic Pulse Field
Authors: Galkina E. G. , Stankiewicz A. , Maziewski A.
Published: July 2007

It is shown that large oscillations of magnetization (induced by fast changes of external magnetic field) in ferromagnets, of orthorhombic symmetry can show quasistochastic features: a slight deviation in initial state essentially changes the magnetization behavior for t → ∞. In contrast to the simplest uniaxial anisotropy case (where the quasistochastic behavior should be expected only after switching the in‐plane field on), the presence of orthorhombic anisotropy creates the new possibility of quasistochastic excitation after switching the external field off. This anisotropy component may also considerably change the ranges of quasistochastic behavior.
Static Multipole Polarizabilities and Shielding Factors for the S‐Electron Moving in the Screened Coulomb Potential
Authors: Kassim H. A.
Published: July 2007

The variational perturbation approach of Rivail and Rinaldi as generalized by Shukla and Easa is utilized to derive a 2L‐pole static polarizability and a shielding factor for the electron in the ground state moving in a screened Coulomb potential of Debye form. The final formulas are reduced to power series of the screening parameter D in the asymptotic region. The special cases discussed by Fowler can readily be obtained from the present generalized form by direct substitution of the corresponding L values.
Inversion of Atom Populations of Crystal Sites at Phase Transitions
Authors: Sugakov V. I.
Published: July 2007

It is shown that at structural phase transitions of first order in the case of the existence of two energy minima per atom in the unit cell and in the vicinity of the phase interface an inversion of the atom populations of crystal sites arises. This phenomenon is explained by the retardation in establishing the equilibrium atom population as compared with establishing the equilibrium values of energy. The system of kinetic equations for the order parameter are solved numerically. If the Landau approximation of the free energy is valid, analytic solutions for order parameter and inverse population are obtained. The peculiarities of the inversion development for different models of phase transitions are considered. The appearance of inversion can cause various coherence effects (acceleration of atoms, emission of electromagnetic waves, emission of sound, etc.).
Potential Based Phonon Dispersion in Thallium
Authors: Saxena K. C. , Rathore R. P. S.
Published: July 2007

A realistic theoretical study to predict the phonon dispersion and binding energy of h.c.p. metals is developed. The total interaction among the constituents is divided into two parts, ion‐ion part and electron‐ion‐electron part. The former part is expressed by the modified form of the generalized exponential potential (MGEP) developed by the present group. To highlight the characteristic features of the MGEP other similar potentials are compared. The latter part is represented by the modified Krebs scheme, involving the dielectric screening due to Vashista and Singhwi. These interactions are blended to develop a model for predicting the binding energy and the phonon dispersion of the scantily studied h.c.p. metals like thallium.
Distribution Function Parameters Determined from Dynamic Mechanical Spectroscopy Data
Authors: Hermida Élida B. , Povolo F.
Published: July 2007

The dynamical properties of linear viscoelastic materials are related to the strength of relaxation as well as to the statistical parameters of the corresponding distribution function. Nowick and Berry established numerically the relationships between the real and imaginary moduli or compliances, the strength of relaxation, and the parameters of a widely used distribution function: the log‐normal one. These relationships are modified, applying a perturbation theory, in order to get the parameters from an internal friction peak measured as a function of temperature. Recently, a modified anelastic element (MAE) has been introduced for describing the mechanical properties, particularly the internal friction, of linear viscoelastic solids. It has been shown that the distribution function associated to the MAE is quite similar to a log‐normal distribution. Therefore, in the present paper the perturbation theory developed by Nowick and Berry is applied to the internal friction peak for the MAE. It is found that the approximate values calculated for the MAE are in excellent agreement with the analytical parameters associated to this element and also with the approximate expressions derived for the log‐normal distribution. However, this treatment is not enough to determine the temperature dependence of the parameters except if very accurate frequency data are measured. Consequently, an alternative procedure is proposed.
Heat Capacity of HTSC at Temperatures above Tc
Authors: Parish J. L.
Published: July 2007

It is proposed that the material of a HTSC at temperatures above Tc contains a new state of matter in which electrons and holes are trapped in a lattice wave. The heat capacity of this new state is calculated, and it is found to be much larger than that of a normal metal.
Spin Waves in Magnetic Bilayer Films
Authors: Wang Y. Q. , Li Z. Y.
Published: July 2007

The relation of pinning parameters to the uniaxial anisotropy fields of bilayers is discussed in the interface rescaling approach. The effects of the interface, surface, and bulk anisotropy parameters on the spin wave energy and the amplitudes of the spin wave as well as its localization are studied in detail.
Coupled Magnetoelastic Resonances in Garnet Crystals Studied by Light Scattering
Authors: Strotmann M. , Dötsch H. , Sure S. , Lührmann B. , Staas O.
Published: July 2007

Films of yttrium iron garnet are grown by liquid phase epitaxy on substrates of gadolinium gallium garnet (GGG) of 5 mm thickness and orientation [111] or [110]. The ferrimagnetic resonance is excited at frequencies up to 2 GHz. Due to the magnetoelastic interaction standing elastic waves across the thickness of the crystal are induced. They have constant frequency separation of 350 kHz. Optical Bragg diffraction by these resonances is studied at a wavelength of 633 nm, yielding a comb structure of stable light oscillators at twice the excitation frequency. From the measurements the ratio P44/ΔP for GGG is derived. At high power excitations instability oscillations of the ferrimagnetic resonance occur; the optical measurements demonstrate a strong nonlinear coupling of these instabilities to the elastic resonances.
Phase diagrams of the spin‐1/2 transverse ising model with random interactions
Authors: El Mir E. , Saber M.
Published: July 2007

The phase diagrams of the spin‐1/2 transverse Ising model with random interactions are investigated within the framework of the effective field theory using an improved configurational averaging procedure. General formulae, applicable to lattices with coordination number z, are given. Numerical results are presented for a simple cubic lattice. It is found that the effects of a transverse field on the phase diagrams exhibit a number of interesting phenomena.
Dependence of EXAFS phase shift parameters on partial charge and atomic number of the ligand
Authors: Murari A. , Chetal A. R.
Published: July 2007

Using the EXAFS data of the copper systems CuO, Cu(BF4)2·6H2O, Cu(ClO4)2·6H2O, Azurite, CuSO4·5H2O, CuS, CuCl, CuBr, and Cul, the phase parameters α1 and β1 are evaluated. It is shown that for the same ligand, the phase parameters α1 and β1 vary inversely with partial charge q. For ligands having different atomic numbers, these parameters change with partial charge and atomic number of the ligand.
Near infra‐red luminescence of Hg2Cl2
Authors: Bryknar Z. , Grasser R. , Himam M. I. , Kon̆áková A. , Scharmann A.
Published: July 2007

Luminescence in Hg2Cl2 crystals excited with UV light or X‐rays is investigated in the near infra‐red (NIR) spectral region up to 1000 nm. Measurements are performed on as‐grown samples and on samples previously exposed to UV light or X‐rays at RT. Three types of luminescence centres denoted A, B, and C are identified, the luminescence of which depends on the concentration of the photochemical products induced by irradiation of the crystals at RT. Thermoluminescence of Hg2Cl2 is observed for the first time. The glow emission is found in the NIR range, too. It is due to radiative transitions in centres A and B. It is concluded that the NIR luminescence of Hg2Cl2 is not an intrinsic emission but originates from crystal defects. Moreover, luminescence of free excitons in Hg2Cl2 is not observed even at 4.2 K and strong excitation with X‐rays or UV light.
Electronic structure of a step on cleaved surfaces of layered copper oxides
Authors: Prosandeev S. A. , Tennenboum I. M.
Published: July 2007

The electronic structure of a step on cleaved surfaces of layered copper oxides is studied in terms of the Green function method. It is shown that if the edges of the steps are formed by Cu atoms, then deep electronic states appear in the forbidden gap preferably as a result of the breaking of CuO chemical bonds. On the other hand, if the boundary atoms are represented by O atoms, the above phenomenon is due to a change (rise) of the potential at the “surface” atoms. The filling of the bands of these states with electrons may give rise to the one‐dimensional surface conductivity. At low electron concentration in the bands, one has to expect a restructuring or the appearance of superconductivity properties in view of the fact that the Fermi level approaches the van Hove singularity.
Characterization of (GaxIn1−x)2Se3 Raman and Infrared Spectra for 0 ≦ x ≦ 0.5
Authors: Dubček P. , Etlinger B.
Published: July 2007

A modified random element displacement model is used to investigate the composition dependence of Raman and infrared spectra of (GaxIn1−x)2Se3. A computer program that enables the simulation of explicit metal site substitution and stressing the tetrahedral character of the structure is developed. A good agreement with experiment is obtained by using a few free numerical parameters indicating that the vibration modes depend mainly on the structure details. A vibration type assignment to the experimental results is possible for isolated peaks, though more than one vibration mode contribute to some of them. Due to the presence of many close modes and their poor optical activity the vibration type assignment is not possible in the range higher than 180 cm−1.