bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of magnetic field reversals on the shape of Mössbauer spectra
Authors: Dzyublik A. Ya. 
Published: July 2007

AbstractThe Mössbauer effect in soft magnetic materials subject to an external radiofrequency magnetic field is analyzed. Assuming the magnetic field at the nucleus to have only one component which periodically alternates general formulas for the emission spectrum as well as for absorption and scattering cross‐sections are obtained. They are applied to the step‐like and harmonic field models. Besides, the expressions are derived for the instantaneous cross‐sections being periodical functions of time. Transient effects are regarded, which arise when a constant magnetic field changes its direction to the opposite one.
On the reorientation of surface magnetization in semi‐infinite ferromagnets
Authors: Zhao Ping‐Bo , Li Bo‐Zang , Pu Fu‐Cho 
Published: July 2007

AbstractBy establishing an effective transfer matrix technique, we calculate the problem of the surface magnetization direction canting between perpendicular and in‐plane states by the classical XY model. Our calculations show many new features which differ from the results obtained by other molecular field approximations. A possible mechanism for the slope discontinuity on the surface magnetization is proposed.
Infrared Spectra of Solid Trifluoroiodomethane
Authors: Anderson A. , Ko Y. M. , Smith W. 
Published: July 2007

AbstractInfrared spectra of solid trifluoroiodomethane, CF3I, at temperatures between 12 and 125 K in both the lattice and internal mode regions are presented and discussed. A reversible phase transition at (115 ± 3) K is confirmed. The upper phase exhibits broad spectral features, characteristic of a disordered or highly anharmonic crystal. At 12 K, the spectra are typical of an ordered harmonic molecular crystal, and are compatible with a centrosymmetric unit cell containing at least four molecules.
Optical properties of (Bi1−xSbx)2Se3 single crystals
Authors: Navrátil J. , Lošťák P. , Drasar Č. , Blachut T. 
Published: July 2007

Abstract(Bi1−xSbx)2Se3 (x = 0 to 0.2) single crystals prepared from elements of 5N purity by means of a modified Bridgman method were characterized by measurements of infrared reflectance and transmittance. Values of the plasma resonance frequency ϵp, optical relaxation time τ, and high‐frequency permittivity ϵ∞ were determined by fitting the reflectance spectra. It was found that the substitution of Sb atoms for Bi atoms in the Bi2Se3 crystal lattice leads to an increase in the ωp values, whereas in the range of higher Sb content the ωp values decrease. This effect is accounted for by a model of point defects in the crystal lattice of (Bi1−xSbx)2Se3. The dependence of the absorption coefficient K on the energy of incident photons was determined from the transmittance spectra. The position of the short‐wavelength absorption edge is discussed. With regard to the longwavelength absorption edge it was found that the values of α in the relation K ∼ λα lie in the interval 2.2 to 2.5, hence the dominant scattering mechanism of the free charge carriers in (Bi1−xSbx)2Se3 crystals at room temperature is the scattering by acoustic phonons.
Diffusion by vacancy mechanism in Ni, Al, and Ni3Al: Calculation based on many‐body potentials
Authors: Debiaggi S. B. , Decorte P. M. , Monti A. M. 
Published: July 2007

AbstractThe self‐diffusion coefficients for the monovacancy mechanism, described in terms of the Arrhenius law, are calculated for Ni, Al, and the intermetallic compound Ni3Al by computer simulation techniques. Many‐body interatomic potentials, based on the embedded atom model, are used together with the static relaxation method to study the static and dynamic properties of vacancies. The defect formation and migration energies, their corresponding relaxation volumes and vibration entropies, are evaluated. Special interest is devoted to the results obtained for Ni diffusion in Ni3Al. The present calculations predict that simple vacancy‐Ni atom interchange jumps (both of ordered and disordered types) are energetically more favourable than the correlated six‐jump cycles. Even though a difference in energies of δ = 0.35 eV favours migration via ordering jumps with respect to disordering jumps, the entropy factors behave in an opposite way suggesting that both types of jumps contribute to the Ni diffusion. Only for low temperatures (T ≤ 770 K) disordering jumps can be neglected. For this case, a pre‐exponential factor D0 = 0.2 × m2 s−1 is obtained.
Diffusion of vacancies under the order‐disorder transition temperature in CuAu
Authors: Hashimoto I. , Yamagata K. , Oketani Y. , Yamaguchi H. 
Published: July 2007

AbstractThe diffusion coefficient of vacancies in CuAu has been measured from the shrinkage rate of voids during annealing. The observations of voids have been carried out by transmission electron microscopy under the order‐disorder transition temperature in the temperature range between 453 and 653 K. The suppression of the diffusion of vacancies emitted from voids is seen at temperatures above 493 K. The reason is discussed briefly in comparison with the results for Cu3Au in terms of the diffusivity of vacancies around the voids.
X‐ray studies of the low‐temperature phase of K2SO4
Authors: Ahmed S. A. 
Published: July 2007

AbstractThe low‐temperature phase transition of potassium sulphate (K2SO4) has been investigated by X‐ray diffraction measurements on polycrystalline material. From the temperature dependence of the lattice parameters it was confirmed that K2SO4 crystals undergo a structural phase transition of second‐order type at 56 K. Above the transition point (β‐phase) the K2SO4 crystal belongs to the Pnam (D) orthorhombic space group with lattice parameters a = 0.74780 nm, b = 1.00707 nm, and c = 0.57701 nm at 293 K. The crystal symmetry of the low‐temperature phase (below 56 K, γ‐phase) is probably monoclinic with space group P21/n11 (C). The low‐temperature phase transformation is thought to be of displacive type.
Transition from spinodal decomposition to the stage of coalescence in undercooled glasses and solid solutions
Authors: Feldman E. P. , Stefanovich L. I. 
Published: July 2007

AbstractThe relaxation of intermediate decomposed structures of glasses and solid solutions in the stages following the complete spinodal decomposition is considered. The time dependence of the characteristic period of the concentration structure both at the early stages of binodal decomposition and at the stage of coalescence is obtained. The temperature dependences of relaxation time and the characteristic scale of the structure are established for a one‐dimensional model. Estimates of the interface thickness at all stages of concentration separation are presented.
Hopping conductivity in p‐type β‐FeSi2
Authors: Lisunov K. G. , Arushanov E. K. , Kloc Ch. , Malang U. , Bucher E. 
Published: July 2007

AbstractThe results of resistivity measurements on p‐type β‐FeSi2 single crystals down to the liquid helium temperature are presented and analyzed within the framework of different hopping conductivity models. The values of the characteristic and transition temperatures, the density of states, and the width of the Coulomb quasigap as well as the localization radius and the dielectric constant are determined.
Slow components in the photoluminescence and scintillation decays of PbWO4 single crystals
Authors: Nikl M. , Nitsch K. , Polak K. , Mihokova E. , Dafinei I. , Auffray E. , Lecoq P. , Reiche P. , Uecker R. , Pazzi G. P. 
Published: July 2007

AbstractThe decay kinetics of PbWO4 luminescence and scintillation is investigated in a broad time scale 10−9 to 10−3 mainly at room temperature using a selected set of PbWO4 crystals. The light sum released in different time gates is estimated showing rather high content of slow recombination processes related mainly to the green PbWO4 emission component. Correlations are found among the absolute green emission intensity, crystal light yield, and the amplitude of very slow processes in the PbWO4 scintillation decay.
Structure of the a band of TI+ in Na1−xKxI mixed crystals
Authors: Inaba M. , Hashimoto S. 
Published: July 2007

AbstractThin Na1−xKxI: TI+ mixed crystals with about 1 μm thickness have been prepared from melt, and the A band of TI+ on the absorption spectra has been observed in the temperature range 11 to 300 K. A distinct splitting of the band is recognized in the composition range of 0.1 < × < 0.6 at low temperatures though it does not occur in NaI: TI+ (x = 0) and KI: TI+ (x = 1). The low‐energy component of the band shifts continuously with x similarly as the peak of the exciton bands. On the basis of the temperature dependence, the structure is attributed to the static perturbation in addition to the dynamical Jahn‐Teller effect.
Optical absorption and photoluminescence of narrow‐Gap Hg1−x−yCdxMnySe single crystals
Authors: Mazur Yu. I. , Tarasov G. G. , Lavorik S. R. , Tomm J. W. , Kissel H. , Hoerstel W. 
Published: July 2007

AbstractThe optical properties of Hg1−x−yCdxMnySe (x = 0.09 to 0.11, y = 0.02 to 0.03) single crystals are investigated by means of infrared transmission and photoluminescence. The photoluminescence is promoted by manganese doping. The presence of Mn significantly improves the structure of mercury selenides. The optical dielectric constant, refractive index, and energy gap are determined as functions of temperature.
Water adsorption on the stepped si(110) surface
Authors: Katircioglu Ş. , Erkoç Ş. 
Published: July 2007

AbstractWe have investigated the possible water adsorption forms on the stepped Si(110) surface. Calculations have been performed by using the empirical tight‐binding method. Two types of adsorption model of water on a single layer stepped Si(110) surface have been considered, one of them is the dissociative type (H, OH) and the other one is the molecular type (H2O). The total electronic energy and TDOS calculations lead to a dissociative type of water adsorption on the stepped Si(110) surface excluding the molecular type as it was found on the flat Si(110) surface.
Coupling with the Jahn‐Teller mode for triplet states of MF6 (M = Mn2+, Cr3+) complexes: Dependence on the M‐F distance and influence on the stokes shift
Authors: Barriuso M. T. , Aramburu J. A. , Moreno M. 
Published: July 2007

AbstractThe microscopic origin of the VE coupling constant with the Jahn‐Teller mode Eg for orbital triplet states corresponding to several excited states of MnF4+6 and the 4T2g state of CrF3−6 is explored by molecular orbital (MO) calculations. VE is shown to be determined by the splittings δe and δt induced in the antibonding e and t levels by a Qθ(∼3z2− r2) distortion and so VE < 0 for the 4T2g state of CrF36 leading to a compressed octahedron as equilibrium geometry. VE values have been derived from self‐consistent charge extended Hückel and MSXα calculations performed at different Qθ values. The results for the 4T1g(G), 4T2g(G), 4T2g(D), and 4T1g(P) states of MnF46 are reasonably close to the experimental figures. For the first excited state 4T1g(G) the value VE ∼ 60 cm−1/pm found for a metal‐ligand distance R equal to 213 pm leads to a Huang‐Rhys factor SE = 1.5 also close to experimental findings. On passing from this case to the 4T2g state of CrF36−[VE] increases by a factor of about two but SE =S 1.2 in agreement with experimental data for Rb2KGaF6: Cr3+. The latter figure implies a Stokes shift E0S(E) due to the Eg mode equal to 1200 cm−1 which is about 50% of the total Stokes shift. As a salient feature it is shown that for both MnF4−6 and CrF3−6 complexes VE strongly depends upon R, as it also happens to the VA coupling constant with the symmetric A1g mode. This reasonably explains the increase of the Stokes shift upon increasing R recently observed for Mn2+−doped fluoroperovskites. Although pure crystalfield (CF) theory gives rise to VE values much smaller than the experimental ones it is shown that, the relation VA/VE = \documentclass{article}\pagestyle{empty}\begin{document}$\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt 2 $\end{document}$\end{document} derivedforthe first excited state of MnF4−6 and CrF3−6 is no far from the results obtained through MO calculations.
Estimation of the local compressibilities for GD3Ga5O12 : Cr3+ and Gd3Sc2Ga3O12 : Cr3+ crystals from their high pressure spectroscopies
Authors: Zheng Wen‐Chen 
Published: July 2007

AbstractAccording to high pressure spectroscopies, in particular, the nearly linear red‐shift of the R‐line at pressures above ≈ 7 GPa for Gd3Ga5O12 : Cr3+ and Gd3Sc2Ga3O12 : Cr3+ crystals, the local linear compressibilities of (CrO6)9− groups in both systems at P ≈ 7 GPa have been determined by using the bond length dependence of the covalency reduction factor obtained from the pressure‐induced spectral shifts of ruby (Al2O3 : Cr3+). Then, the local compressibilities at normal pressure are estimated on the basis of the pressure dependence of compressibility obtained for other garnet crystals. The results are obviously different from the compressibilities of the host crystals. The reasons of this difference are discussed.
Persistent photoconductivity and properties of the Two‐Dimensional electron Gas in modulation‐doped GaInAs/AlInAs heterostructures after illumination
Authors: Saffian B. , Kraak W. , Oelze B. , Künzel H. , Böttcher J. 
Published: July 2007

AbstractThe properties of the two‐dimensional electron gas (2DEG) in MBE‐grown low carrier density Ga0.47In0.53As/Al0.48In0.52As heterostructures after illumination at low temperatures have been investigated. A strong persistent photoconductivity anddrastic changes of low temperature electronic properties were observed. Thepronounced changes of the quantum oscillations of the magnetoresistivity (Shubnikov‐de Haas effect) and of the quantum Hall effect clearly reveal an important increase of both electron concentration and carrier mobility in the two‐dimensional interface layer. The variations of the electronic properties are attributed to photoexcitation of electron‐hole pairs in the GaInAs layer.
A possible new approach of superconductivity
Authors: Rezlescu N. , Gh. Buzea C. , Buzea C. , Agop M. , Ignat M. 
Published: July 2007

AbstractA new superconducting mechanism is postulated by substituting the exchange interaction between the pairs by an interaction on the “subquantic medium”. Equating the potential of a spin‐polaronlike distribution to the “subquantic potential”, a nonlinear equation for the density of states is obtained. Solving this equation using the WKBJ method, a splitting of the density of states is noticed under particular conditions, the result is understood as the formation of pairs.
Mean‐field insight into the plasmon mechanism of the pairing arrangement in the one‐dimensional electron system
Authors: Yanetka I. 
Published: July 2007

AbstractThe mean‐field temperature of the insulating transition is obtained for the one‐dimensional electron system with the interparticle interaction that can be expressed with the help of the dielectric response function. To illustrate the results a detailed calculation of the transitiontemperature is presented for the one‐dimensional system with the tight‐binding particle spectrum and with the effective interparticle interaction of Coulomb type that is evaluated in the plasmon‐pole approximation.
Numerical solution to the general one‐dimensional diffusion equation in semiconductor heterostructures
Authors: Harrison P. 
Published: July 2007

AbstractA method of solving numerically the one‐dimensional diffusion equation for arbitrary profiles and arbitrary functional dependencies of the diffusion coefficient on the position, diffusant concentration and the time, is described. The technique is applied to a variety of diffusion problems in semiconductor quantum wells to illustrate its power and versatility. In particular solutions are shown for diffusion of graded interfaces, a concentration dependent diffusion coefficient, and the effect of a depth and time dependent diffusion coefficient on a superlattice, as occurs in ion implantation and the subsequent annealing out of the resulting radiation damage. The depth dependence of the intermixing due to ion implantation and subsequent rapid thermal anneal, of a GaAs/Ga1−xAlxAs multiple‐quantum‐well structure, is deduced from the broadening of the low temperature photoluminescence emission.
Study of the localization lengths in non‐periodic GaAs/Al0.3Ga0.7As superlattices
Authors: Usher Marilyn , Ranganathan Radha 
Published: July 2007

AbstractElectronic states and the wavefunction localization lengths for non‐periodic GaAs/Al0.3Ga0.7As superlattices are calculated and also studied experimentally using photoluminescence. Non‐periodicity causes the first bound state to shift down in energy. A relation between the shift in energy from the periodic case and the wavefunction localization length is derived and used to obtain the localization length experimentally from photoluminescence measurements. The localization length thus obtained is compared with the results from a direct calculation of the wavefunction.
Exchange coupling between two magnetic layers in a quasi‐one‐dimensional potential well
Authors: Wang Zhongcheng , Wang Shaofeng , Hou Weihong 
Published: July 2007

AbstractExchange coupling between two magnetic monolayers mediated by electrons confined in a quasi‐one‐dimensional potential well is investigated. By using a Green's‐function method and approximate expansion, an analytic expression is derived for the weak coupling within the contact interaction approximation. As a main result of the quantum size effect, the number of occupied levels and the Fermi energy are found to be periodic functions of the sample thickness. If the anisotropy in the effective electron mass is taken into consideration, the period is given by \documentclass{article}\pagestyle{empty}\begin{document}$ T = \sqrt[3]{{{{\pi \mu _\parallel } \mathord{\left/ {\vphantom {{\pi \mu _\parallel } {\left({6n_0 \mu _ \bot } \right)}}} \right. \kern-\nulldelimiterspace} {\left({6n_0 \mu _ \bot } \right)}}}} $\end{document}, where μ| and μ⊥ are the effective electron mass in the surface and growth direction, respectively, and n0 is the electron density for one spin. Because of the quantum size effect, the exchange coupling cannot be considered as a simple oscillatory function of the distance between the two magnetic layers. It depends on the distance between the two magnetic layers as well as on the distance from the magnetic layer to the sample surface. For some distance from the magnetic layer to the sample surface, the exchange coupling with the distance between two magnetic layers shows a similar analytic behaviour as the RKKY interaction does. However, for some other distance, there may be just a strength oscillation of the ferromagnetic coupling.
Effective mass of a polaron in a quantum wire under a strong magnetic field
Authors: Lu Tianquan , Zheng Yisong , Zhang Chengxiang , Wu Xuhong 
Published: July 2007

AbstractUsing the Lee‐Low‐Pines variational method the effective mass of a polaron in a rectangular quantum wire subject to a strong uniform external magnetic field along the wire length is studied. Taking the GaAs quantum wire as an example numerical results are given. The results show that the effective mass of the polaron is dominated mainly by the smaller dimension of the quantum wire cross section and the external magnetic field has an interesting influence on it.
1/N expansions for the U = ∞ Hubbard model: Comparison between X‐operator and slave‐boson approach
Authors: Gehlhoff L. 
Published: July 2007

AbstractWe consider the large‐spin‐degeneracy (N) version of the U = ∞ one‐band Hubbard model and present a systematic 1/N expansion method which is based on Hubbard's X‐operator formulation and a Baym‐Kadanoff expansion. We compare this alternative X‐operator approach with the customary time‐continuum slave‐boson (SB) functional‐integral treatment, which has recently been criticized. In particular, we give a detailed derivation of the density Green's function within the new approach and compare the leading‐order results with those as obtained with the commonly used SB treatment, finding total agreement.
Theoretical study of resonance phenomena in n‐fold non‐periodic barrier structures
Authors: Zhao X. D. , Yamamoto H. , Taniguchi K. 
Published: July 2007

AbstractResonant tunneling is studied systematically for finite non‐periodic barrier structures with arbitrary potential profiles, which are considered as a network connecting alternately the generalized‐barrier unit with the phase delay unit in series. Analytical expressions of the transmission coefficient and the resonance condition for these structures are derived by taking into account the mass difference between well and barrier layers. It is found that a quasi‐periodic mode may exist in non‐periodic barrier structures. An optimum group of resonant peaks composed of single unity transmission and (n − 2) near‐unity resonant peaks will occur when both the unity resonance condition and the quasi‐periodic mode condition hold simulteneously.
High Pressure Magnetophotoluminescence in Diluted Magnetic Semiconductors Cd1−xMnxSe and Cd1−xCoxSe
Authors: Kuroda N. , Matsuda Y. 
Published: July 2007

AbstractThis paper reviews experimental studies on the magnetophotoluminescence in diluted magnetic semiconductors Cd1−xMnxSe with x = 0.01, 0.05, 0.10, and 0.25 and Cd1−xCoxSe with x = 0.012 at 1.4 and 4.2 K under hydrostatic pressures up to 2 GPa. The studies focus attention to the pressure dependence of the magnetic dichroism of the 1 s exciton state under magnetic fields of 0 to 27 T. Pressure strengthens the exciton‐Mn(Co) and Mn(Co)‐Mn(Co) exchange interactions. An analysis of these results in terms of the kinetic exchange theory shows that the on‐site Coulomb energy U and the chargetransfer energy Δ are reduced markedly by pressure.
Effect of Pressure on the Refractive Index and the Band Gap of Cesium Halides
Authors: Johannsen P. G. , Reiss G. , Bohle U. , Holzapfel W. B. 
Published: July 2007

AbstractThe refractive indexes of CsCl, CsBr, and CsI show a strong nonlinear density dependence. This behaviour can be related to the closure of the band gap by means of a constant‐joint‐density‐of‐states model for the dielectric function. The results are discussed with respect to the dielectric properties of other AB compounds.
Shubnikov‐de Haas Oscillations in Fe‐ and Co‐Doped HgSe under Pressure
Authors: Neifeld E. A. , Demchuk K. M. , Harus G. I. , Boubnova A. E. , Domanskaya L. I. , Shtrapenin G. L. , Yu. Paranchich S. 
Published: July 2007

AbstractWe have investigated the effect of pressure on Shubnikov‐de Haas oscillations in the gapless semiconductor HgSe doped with Fe and Co. For HgSe(Fe) an increase of pressure results in a decrease of the electron concentration in accordance with the Kane model for constant Fermi energy. In contrast, in HgSe(Co) the electron concentration is independent of pressure, i.e. the Fermi level is not pinned.
Competition of Deep and Shallow Impurities in Wide‐Gap II‐VI Semiconductors under Pressure
Authors: Weinstein B. A. , Ritter T. M. , Strachan D. , Li M. , Luo H. , Tamargo M. , Park R. 
Published: July 2007

AbstractThe effects of applied pressure on deep defects, shallow ↔ deep competition, and related doping problems in II‐VI semiconductors are reviewed. Photoluminescence studies to 100 kbar (at 7 K) on high purity ZnSe, and on several ZnSe samples doped with 1016 to 1019 cm−3 Cl, Ga, N, P, and As reveal striking differences between the pressure‐shifts of broad‐band features involving acceptor and/or donor deep states, and excitonic lines due to shallow band‐edge states. The binding energies of observed deep acceptor states tend to decrease with pressure, suggesting that compression acts to destabilize these states against competing shallow hole levels. A deep donor level assigned to an excited state of donor‐vacancyzn complexes emerges from the electron continuum in n‐type Ga‐ and Cl‐doped samples at ≈︁25 to 28 kbar. This previously unknown state should not affect doping in ZnSe1−xTex alloys since it arises from existing compensation centers.