bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plasma Excitation in Semiconductors Containing Extended Scattering Centers
Authors: Gerlach E. , Kistinger S. 
Published: July 2007

AbstractDynamical carrier scattering caused by extended crystal perturbations (models for clusters, doping inhomogeneities, precipitations etc.) is studied using the “energy‐loss method”. Based on Mermin's dielectric function multiple scattering is selfconsistently taken into account. Since extended perturbations are mainly described by small wavevectors, plasmon excitation by scattering strongly exceeds single particle excitation. It is conceivable to utilize the dominant plasma‐peak to characterize perturbations in semiconductor crystals.
Interpretation of 57Fe Mössbauer Measurements on Nd2Fe14B at 83 and 295 K
Authors: Shi Yan , Jin Hanmin , Jin Mingzhi 
Published: July 2007

AbstractThe 57Fe Mössbauer spectrum of the Nd2Fe14B compound at 83 K is analyzed with eighteen Zeeman sextuplets by taking into account of the splittings of the six Fe sites (Fec, Fec, Fej1, Fej2, Fek1, and Fek2) into 2, 2, 3, 3, 4, and 4 magnetically inequivalent sub‐sites. The spectrum at 295 K is analyzed with six Zeeman sextuplets. The electric quadrupole splittings at each Fe site are calculated on the basis of a point charge model with different electric charges for Fe and B. When the charges of Nd, Fe, and B are 3e, 2e and zero (e > 0), the calculated results coincide with those obtained by fitting the Mössbauer spectra measured at 83 and 295 K.
Magnetic and Mössbauer Studies of Anion‐Substituted Nickel Ferrites
Authors: Bayukov O. A. , Ikonnikov V. P. , Savitskii A. F. 
Published: July 2007

AbstractThe measurements of the sublattice magnetizations in the spinels NiFe2O4−xSx are reported. Using the superexchange model the 3d‐electron transfer parameters of ligand‐cation and the integrals of cation‐cation exchange interactions are determined.
Luminescence Properties of {(CH3)4N}2ZnCl4 Single Crystals
Authors: Martín A. , López F. J. , Arend H. 
Published: July 2007

AbstractResults on the X‐ray induced luminescence (RL), after‐glow (AG), and thermoluminescence (TL) spectra in the range 10 to 300 K of {(CH3)4N}2ZnCl4 single crystals are presented and compared with previous results for Rb2ZnCl4 and K2ZnCl4. The emissions for the three cases are proposed to be associated to intrinsic electron‐hole recombination processes.
Raman Scattering in Ferroelectric TlGaSe2. Soft Mode and Order Parameter
Authors: Burlakov V. M. , Yakheev M. R. 
Published: July 2007

AbstractThe Raman scattering spectra of soft and rigid modes in TlGaSe2 are investigated over a wide temperature range. The interaction between soft and rigid modes is observed from the description of the experimental spectrum within a model of interacting harmonic oscillators. Temperature dependences of the soft mode frequency and halfwidth are confirmed. The splitting of the rigid Raman mode in the ferroelectric phase is also detected.
Resonant Raman Scattering near E1 + Δ1 in CdxHg1−xSe
Authors: Kumazaki K. 
Published: July 2007

AbstractRaman scattering by phonons is measured in CdxHg1−xSe with x = 0 to 0.3 on (100), (110) and (111) surfaces near the E1 + Δ1 energy gap at room temperature. From these measurements, the composition dependence of the HgSe‐like TO and LO mode frequencies is obtained. The plasmon‐LO phonon coupled modes and a cluster mode are also observed. Effective high‐frequency dielectric constants calculated by the extended Lyddane‐Sachs‐Teller relation show a discontinuity near the semimetal‐semiconductor transition point. This discontinuity is attributed to the contribution of interband terms to the dielectric function. The results obtained from the Raman measurements are compared with those from far‐infrared measurements.
Generalized Transfer‐Matrix Description of the Optical Properties of Spatially Dispersive Periodic Metal Multilayers
Authors: Trutschel U. , Golz M. , Abraham M. 
Published: July 2007

AbstractA transfer matrix formalism is used to treat in a general way the optical response of different kind of metal superlattices. The dispersion relation of infinite and semi‐infinite superlattices and the reflectivity of semiinfinite superlattices are calculated. Spatial dispersion is included via additional boundary conditions. Each unit cell of the superlattices can be built up by an arbitrary number of layers with local and/or nonlocal dielectric functions. In the case of a spatially dispersive double layer unit cell the explicit dispersion relation is derived. The limits when one of the layers is local as well as the complete local case are shown to be included.
Effect of Pressure on Lattice Parameters of Intercalation Compounds MxTiS2 (M = Fe and Ni)
Authors: Negishi H. , Ōhara S. , Inoue M. 
Published: July 2007

AbstractLattice parameters a and c of 1T‐CdI2 type layered TiS2 crystals and its intercalation compounds MxTiS2 (M = Fe and Ni; x = 0.05 and 1/4) are measured under hydrostatic pressures up to 1.2 GPa at room temperature. Both, a and c, of these crystals are decreased linearly with pressure, and their linear elastic moduli are strongly dependent on the guest concentration x. The effect of 3d metal intercalation on the structural properties is qualitatively discussed.
Laser‐Induced F‐F− Conversions in KCl Crystals
Authors: Subrahmanyam R. , Murti Y. V. G. S. 
Published: July 2007

AbstractF centers in KCl crystals are converted to F− centers by bleaching with radiation from a low power HeNe laser. Growth curves of these centers are constructed by monitoring the optical absorption at 720 nm at several temperatures. The growth curves are analyzed and the thermal ionization energy of the F− center is deduced. The results are discussed in terms of the kinetics of the processes.
Dynamic Effects in a New Substitutional Center of Trivalent Iron in Quartz
Authors: Stegger P. , Lehmann G. 
Published: July 2007

AbstractAfter exchange of Li against Na in a natural quartz of high quality by electrolysis at higher temperatures a new center of Fe3+ with monoclinic site symmetry at room temperature is detected by electron paramagnetic resonance (EPR). At temperatures below 200 K the linewidths of the EPR spectra increase considerably, and at about 60 K a signal of a triclinic center with a well‐resolved quartet hyperfine splitting appears instead. Thus the charge‐compensating Na ion evidently changes rapidly between two equivalent positions at higher temperatures. An estimate of the activation energy for this hopping process is obtained from the temperature dependence of the linewidths for the monoclinic spectrum.
Exciton‐Grating Induced Light Mixing at the Giant Two‐Photon Resonances of Excitonic Molecules in CuBr
Authors: Mizutani G. , Nagasawa N. 
Published: July 2007

AbstractIt is shown that in CuBr crystals a coherent scattering process where the exciton population grating and the excitonic molecule are involved is present, from the experiment of a three beam non‐degenerate optical mixing. This process cannot be described by the 3rd order optical nonlinearity but at least a 5th order non‐linearity is necessary.
Electronic Absorption Spectrum of Ni2+ Ions Doped in Zinc Thallium Sulphate Hexahydrate
Authors: Rao J. L. , Reddy M. R. , Lakshman S. V. J. 
Published: July 2007

AbstractOptical absorption spectra of Ni2+ ions doped in zinc thallium sulphate hexahydrate (ZT1SH) are studied at room and liquid nitrogen temperatures. The spectrum shows characteristic features of Ni2+ ions in octahedral crystalline fields. At liquid nitrogen temperature, one of the bands exhibits splitting. The fine splitting is interpreted as due to spin‐orbit interaction. From a detailed analysis of the bands of the spectrum, the crystal field parameters B, C, Dq, and ξ are evaluated.
On the Binding Energies of D− States in Doped Germanium. Effects of Valley‐Orbit Corrections and Compressive Uniaxial Stress
Authors: Weber G. , Oliveira L. E. 
Published: July 2007

AbstractThe effects of compressive uniaxial stress along the [111] direction and of valley‐orbit corrections on the binding energies of D− states in Sb‐ and P‐doped germanium are calculated. A variational procedure is used with a Chandrasekhar‐type of variational wave function. The model Hamiltonian takes into account electron‐electron interaction, valley‐orbit corrections, and stress effects. The results show similar behavior as in previous work on doped silicon and quantitatively agree with available long‐wavelength photoconductivity measurements for doped germanium.
The Local Electron‐Spin‐Density Fluctuation Mechanism of the Superconductivity in Narrow‐Band Metals
Authors: Grebennikov V. I. , Sokolov O. B. 
Published: July 2007

AbstractA novel mechanism is proposed of electron pairing due to local electron‐spin‐density fluctuations in copper oxide superconductors. Self‐consistent equations are formulated. Their input data are the density of states curve and the intra‐atomic electron repulsion parameter. The pairing interaction has a peak at small energy transfers. The superconductivity region is limited both, from below and from above the initial‐repulsion values. The gap width to critical temperature Tc ratio is large; Tc is higher than its value in the phonon mechanism.
Nonthermal Spread of Quantum Levels in Solids Due to Defects
Authors: Dmitriev A. I. , Lashkarev G. V. 
Published: July 2007

AbstractThe quantum level spread is treated in terms of the Dingle temperature, TD. The universal nature of the nonthermal spreading of the Landau levels in solids is established and explained. The importance of the low‐angle scattering of current carriers for the quantum oscillation effects is shown. The effect of the random electrostatic potential fluctuations on the magnitude of the quantum level spread is studied in detail. Experimental data are compared with theory for a wide range of compositions, x, and carrier concentrations, N, in Pb1−xSnxTe alloys.
Mössbauer Radiation Transfer in a Plane Layer. Anisotropic Case
Authors: Gabrielyan R. G. , Kotandjian Kh. V. 
Published: July 2007

AbstractTraditionally only single resonance scattering is taken into account in the Mössbauer spectroscopy for scattering. In the present paper as in previous papers a more precise theory is developed taking into account multiple scattering of the Mössbauer radiation transfer using the theory of the optical radiation transfer. The frequency‐modulated γ‐radiation scattering in a plane parallel layer is also considered.
A New Type of Bond‐Dilution Problem in a Ferromagnetic Insulator with a Fractional Random Coordination Number
Authors: Sarmento E. F. , da Cruz H. R. , Kaneyoshi T. 
Published: July 2007

AbstractThe ferromagnetic phase stability limits (or phase diagrams) of a quenched bond‐diluted spin‐ ½ transverse Ising ferromagnetic insulator with a fractional random coordination number are studied within the framework of the effective‐field theory with correlations. The changes of transition temperature and critical concentration with the topology of the network (or the averaged connectivity) are examined in the zero transverse field. The results obtained are compared with those available in the literature. The influences of transverse field on the critical frontiers are also obtained.
Approximate Solution for a Two‐Dimensional Anisotropic Ferromagnetic Spin Lattice with Bloch Wall and Bloch Line. I. Analytic Computation
Authors: Knoop U. , Heber G. 
Published: July 2007

AbstractFor a two‐dimensional spin lattice with exchange and local anisotropy nonlinear equations are deduced. Under the condition that the spin lattice contains a Bloch wall and a Bloch line, approximate solutions are derived in the classical continuum approximation.
Temperature Dependent Frequency Shifts in the Resonance Absorption and Resonance Fluorescence Scattering of Mössbauer γ‐Quanta
Authors: Follath R. , Jex H. 
Published: July 2007

AbstractThe relativistic Doppler effect in the resonance absorption and resonance fluorescence scattering of Mössbauer γ‐quanta of a 57Co source is investigated in the temperature range 295 K ≦ T ≦ ≦ 585 K. The temperature shift of the resonance is d(ln ω)/dT = − (2.38 ± 0.07) × 10−15 K−1 in absorption and − (2.67 ± 0.10) × 10−15 K−1 in backscattering. The data are compared with Bragg scattered Mössbauer γ‐quanta from the (200) reflection of NaCl in the same temperature range. A limit d(ln ω)/dT ≦ 7.5 × 10−17 K−1 is obtained.
Effect of High Pressure on the Optical Transmission Spectra of AIIIBIIIC Crystals
Authors: Prins A. D. , Allakhverdiev K. R. , Babaev S. S. , Guseinov S. S. , Mekhtiev E. I. , Shirinov M. M. , Tagyev M. M. , Dunstan D. J. 
Published: July 2007

AbstractThe influence of high pressure up to 13 GPa on the optical transmission spectra of layered AIIIBIIIC crystals was investigated. The value of the pressure coefficient of the transmission spectra at 30% transmission is reported. Results indicate that these materials undergo a series of phase transitions in the region investigated.
The conversion of electronic centres into U and OH‐ centres
Authors: Topa V. , Ioan A. , Iliescu B. , Mitroaica G. 
Published: July 2007

AbstractA quantitative treatment is made of F → U conversion in H2 in very pure KC1 crystals and the conversion of electronic centres (like Ag−, Cu−, Tl−, Pb in U centres by the same treatment. This fact gives the possibility to elaborate a method for detecting negative metal ion centres. By thermal treatment in water vapour, electronic centres like Ag−, Cu−, Tl−, Pb are transformed mainly into OH− ions and colloids of heavy metal elements.
On the decay properties of the M′ center in LiF crystals
Authors: Bosi L. , Nimis M. 
Published: July 2007

AbstractFor the first time properties concerning the luminescence decay time as well as the relative quantum yield of M′ center in LiF X‐ray irradiated samples are simultaneously and accurately investigated as a function of temperature in the range 12.5 to 335 K. Some discrepancies are found between the decay time values and those obtained by other authors in incomplete runs of measurements. The explanation of this difference may be connected to the coloration process and in particular to the generally high M′ center concentration: on the contrary the M′ center concentration in the samples investigated is low but nevertheless typical for laser operation. Data analysis indicates that more than one nonradiative process is involved in the M′ center decay. It is also ascertained that at fixed temperatures the decay time is independent of the M′ center concentration in the range investigated (i.e., restricted to low concentrations) and of the ageing of the samples.
Local phonons in crystals with electron centres
Authors: Lakhno V. D. , Chuev G. N. 
Published: July 2007

AbstractThe changes are investigated in the phonon spectrum for the F‐centre in the presence of excess electron. The frequencies of local phonons for the ground and the first excited self‐consistent states of the F‐centre in KC1 are calculated. The adiabatic approximation is used to determine a secondorder correction to the energy for self‐consistent states in the F‐centre. As a limit the resting polaron is considered. For excited self‐consistent states local modes are found with frequencies larger than in optical phonons. It is also found that excited self‐consistent states of the polaron show a phonon (pseudo Jahn‐Teller) instability.
Green functions for polariton modes in magnetic superlattices
Authors: Raj N. , Tilley D. R. 
Published: July 2007

AbstractThe linear response of magnetic‐polariton modes in an infinitely extended magnetic superlattice to an r.f. applied magnetic field is considered. The resulting Green functions are given in mixed position, wavevector form and also in wavevector, wavevector form. As is expected, the poles of the derived Green functions give the dispersion relations for magnetic polaritons in a bulk magnetic medium and also in a magnetic superlattice.
Construction and application of the Green's function for stepwise constant potentials
Authors: Trott M. , Schnittler Ch. 
Published: July 2007

AbstractThe path‐integral‐inspired approximation method is a convenient tool for the construction of a WKB‐like Green's function. This method is generalized to the case of potentials with finite steps by investigating the exact Green's function of a single finite step. To demonstrate the utility of this method the single quantum well is studied in detail: For the stepwise constant potential the density of states of the bound as well as of the continuum states is given. For a smooth potential bottom semiclassical quantization rules are derived for different band bendings. The series representation of the Green's function allows the derivation of an appropriate local density of states necessary for a modified Thomas‐Fermi approximation.
Distortion of the crystal field in the van Vleck paramagnet LiTmF4 activated by isovalent impurities
Authors: Aminov L. K. , Vinokurov A. V. , Kurkin I. N. , Kostetskii Yu. Yu. , Korableva S. L. , Salikhov I. Kh. , Sakhaeva S. I. , Teplov M. A. 
Published: July 2007

AbstractThe spin‐lattice relaxation times of Ce3+, Nd3+, Yb3+ ions are measured in LiTmF4 single crystals at temperatures (1.6 to 5.0 K) and frequencies 9.4 and 23.0 GHz. An observed exponential dependence of the relaxation rate on temperature, T ∼ exp (−Δ/kT), shows that relaxation proceeds through Van Vleck Tm3+ host ions, and for the Nd3+ ion it is possible to distinguish the contributions to relaxation of the nearest and more distant coordination spheres. The distinction of the activation energy Δ from the excitation energy of the lowest Tm3+ doublet state in the ideal crystal (32 cm−1) is explained by a strong distortion of the crystal field at the Tm3+ ions nearest to the impurity. Investigations of the optical absorption spectra of Tm3+ ions in pure and doped LiTmF4 single crystals are in good agreement with this point of view.
Wannier functions for d‐band of ferromagnetic nickel
Authors: Modrak P. , Wojnecki R. 
Published: July 2007

AbstractThe method of direct variational calculation of Wannier functions is applied to the ferromagnetic nickel. The calculations are performed within the framework of the unrestricted Hartree‐Fock theory. The Slater‐Koster parameters obtained are compared with other results and with the parameters used in model Hamiltonians for ferromagnetic nickel.
Temperature dependence of carrier trapping in bulk vitreous GeSe3 from transit time measurements
Authors: Calas J. , Abdel‐maksoud S. , Averous M. 
Published: July 2007

AbstractTransit time measurements in the low signal approximation are reported for bulk vitreous GeSe3. The temperature range investigated is 100 to 300 K. The shape of the transient current can only be explained by a model with two trapping centers, a shallow one and a deep one. The shallow level is described by Tt1 and Td where Tt1 and Td are the times spent in the free state and on the trap, respectively. For the deep level the probability for a carrier reemission is neglected; the time Tt2 spent in the free state before trapping is only taken into account. The spectral sensitivity for photocarrier creation is also given with a maximum at 2.7 eV, i.e. higher than the energy of the band gap.
Anomalous magnetic field dependence of electron mobility in anisotropic ferromagnetic semiconductors
Authors: Okladnoy Yu. G. 
Published: July 2007

AbstractThe magnetic field dependence of the electron mobility in an easy‐axis ferromagnetic semiconductor is investigated for the case when the magnetic subsystem is described by a Heisenberg Hamil‐tonian with a weak anisotropy. It is found that, under definite conditions, the transversal magnetic field leads to an increase in magnon concentration and, accordingly, to a decrease in the electron mobility, while for isotropic ferromagnetic semiconductors only a decrease of the concentration and an increase of the mobility can take place for increasing magnetic fields.
Determination of deformation potential constants of arsenic
Authors: Golban I. M. 
Published: July 2007

AbstractThe galvanomagnetic coefficients of arsenic are calculated by means of a variational method taking intravalley scattering of charge carriers on longwave acoustic phonons into account. The experimental data of galvanomagnetic phenomena in weak magnetic fields are processed with the help of the formulae obtained and the constants of deformation potentials of electrons and holes are calculated in a wide temperature range (77 to 305 K).
The behaviour of the vortex state in magnetic superconductors
Authors: Saif A. G. 
Published: July 2007

AbstractThe distribution of the magnetic field inside a ferromagnetic superconductor (FS) is developed. The behaviour of the surface pinning in different geometries of FS system is considered. It is shown that, for FS systems, the superheating field is of the order of thermodynamic critical field for magnetic superconductors, H.
Mössbauer lineshape in the case of diluted ferromagnetic alloy thin films
Authors: Urbaniak‐Kucharczyk A. , Osetek Z. 
Published: July 2007

AbstractThe theory of Mössbauer line shape in fluctuating environment is applied to the case of thin film of a diluted alloy. The distribution of the spin autocorrelation time characterizing the line shape in the vicinity of phase transition point across the sample is calculated. It is shown that the change of concentration of magnetic atoms in diluted alloys leads to a variety of Mössbauer spectra at the same sample temperature. All the results obtained are calculated for the particular case of S = 1/2 and for a film with b.c.c. lattice, although another crystallographic lattices may be consider as well.
The Ising model of the two‐dimensional quasiperiodic lattice
Authors: Doroba A. , Sokalski K. 
Published: July 2007

AbstractThe magnetic structure of a two‐dimensional system of Ising spins arranged in the Penrose‐like lattice is investigated by means of the Bethe‐Peierls‐Weiss method applied to the nonperiodic lattice. Six types of spin‐sites are distinguished and seven exchange integrals depending on the spin enviroment are introduced. It is checked that this method applies only to the case of all nonzero exchange integrals. Phase diagrams and the thermodynamic and magnetic quantities for various points in parameter space are calculated. The stable and unstable magnetic ordered phases are found. For the antiferromagnetic case points of full compensation appear.
On the relation between structural phase transitions and spin reorientation transition in anisotropic ferromagnets
Authors: Schreiber J. , Bläsing J. , Flach S. 
Published: July 2007

AbstractOn the basis of Hollstein‐Primakoff transformation for the Heisenberg model with anisotropy a new theoretical description of the spin reorientation transition in ferromagnetic systems is given. An effective Hamiltonian is derived, which is identical with the scalar Φ4‐lattice model of structural phase transitions. Especially the appearance of precursor clusters of the low temperature phase above the phase transition point is discussed. If the reorientation transition takes place at sufficiently low temperatures the existence of defect pinned cluster states can lead to glass‐like behaviour. Experimental consequences are considered. In relation to the anomalous properties of high‐Tc superconductors special attention is paid to the importance of a crossover from a soft mode or mean‐field‐like behaviour into the regime of cluster fluctuations in strongly non‐linear dynamical systems.