bluuebunny/crossref_metadata_2025_split huggingface dataset:
A study of spin interaction in a manganese‐substituted zinc ferrite by neutron spectroscopy
Authors: Ligenza S. 
Published: July 2007

AbstractInelastic neutron scattering is studied on a manganese‐substituted zinc ferrite at temperatures between 5 and 293 K. The obtained neutron spectra are interpreted basing on the 6S5/2‐term splitting of the Fe3+ ion in an octahedral B‐site. The transition energy peaks connected with different magnetic environment of Fe3+ (B) ions are observed. The six‐fold 6S5/2‐term splitting and the excited neutron transition are discussed in terms of a phenomenological spin‐Hamiltonian, assuming combined interaction of a static magnetic field and a static electric field gradient with magnetoelectric moments of the 3d5 electron shell. In addition, a superparamagnetic behaviour is studied by neutron diffraction and Mössbauer effect measurement. Quasielastic coherent scattering of neutrons due to superparamagnetic clusters is observed.
The lattice distortion around interstitials in F.C.C. metals
Authors: Miller K. M. , Heald P. T. 
Published: July 2007

AbstractThe displacement field produced by the body centred interstitial and the 〈100〉 spilt interstitial in aluminium, nickel, and the noble metals is calculated using a discrete lattice model. It is assumed that the host atoms interact amongst themselves through a pairwise potential which extends out to second‐nearest neighbours and the short‐range repulsion between the interstitial and near neighbour host atoms is represented by either a Born‐Mayer or Morse potential. With the exception of aluminium the relaxation volume around the 〈100〉 spilt interstitial is similar to that around the body‐centred configuration and furthermore the differences in the results for the two potentials are quite small. For each metal the relaxation volume around an interstitial is found to be significantly larger than that previously calculated for a vacancy.
Pressure effects on magnetic phase transitions in FeRh and FeRhIr alloys
Authors: Vinokurova L. I. , Vlasov A. V. , Pardavi‐Horváth M. 
Published: July 2007

AbstractThe effect of quasi‐hydrostatic pressures up to 100 kbar is investigated on the phase transitions of Fe1−xRhx alloys by resistivity measurements. The pressure dependence of the first order antiferromagnetic (AF) to ferromagnetic (FM) phase transformation temperature dTk/dp = 4.4 to 5 K/kbar. The pressure dependence of the second order FM to paramagnetic (PM) transition, i.e. that of the Curie‐point is dTC/dp = −0.7 K/kbar. At about 60 kbar the thermal hysteresis diminishes, and above the range of the co‐existence of three phases (AF—FM—PM) the pressure dependence of the AF—PM transition is characterized by dT/dp = 0.6 to 1.0 K/kbar. The AF—PM transition is investigated in an Ir‐substituted alloy (Fe44Rh49.5Ir6.5) also, where dT/dp = 0.6 K/kbar.
Dynamical study of the temperature dependence of grüneisen parameters in alkali metals
Authors: Singh V. P. , Hemkar M. P. 
Published: July 2007

AbstractUsing a non‐central force model the microscopic Grüneisen parameters γq, j and the effective value γG at different temperatures are calculated for the alkali metals in terms of elastic constants and their pressure derivatives. The microscopic Grüneisen parameters γq, j are calculated as a function of wave vector q along the principal symmetry directions [100], [110], [111], [210], [211], and [221] and the values are averaged over the wave vector space in the first Brillouin zone using the modified Houston spherical six term integration method. The results obtained for γG show a fairly good agreement with the experimental observations.
Dynamical properties of crystals of Sr(NO3)2, Ba(NO3)2, and Pb(NO3)2. II. Temperature dependence of the infrared spectra
Authors: Bon A. M. , Benoit C. , Giordano J. 
Published: July 2007

AbstractReflective infrared spectra of three single crystals of strontium nitrate, barium nitrate, and lead nitrate are investigated between 10 and 3500 cm−1 at temperatures from 10 to 293 K. The temperature behaviour of the dispersion parameters, frequencies, strengths, and damping obtained from classical dispersion relation is analyzed in order to compare, first the miscellaneous modes of the same crystal and then of different crystals. The case of Sr(NO3)2 which presents an anomaly in the infrared spectra corresponding to a phase transition is studied in more depth.
On the quantum mechanical foundation of classical shell models in lattice dynamics
Authors: Niedermann H. P. , Wagner M. 
Published: July 2007

AbstractThe approach is based on the adiabatic principle and the harmonic approximation. The aim is to find those quantum mechanical approximations which are necessary to derive expressions of the same structural form as the classical shell model equations of the lattice dynamics of ionic crystals. To this purpose the long range interaction of the ionic dipoles is treated in first order perturbation theory, whereas for the short range part of the adiabatic potential a more restricted approximation is used. By this means equations of motions are obtained of the form of the equations of the classical shell models. But in contrast to the phenomenological models by quantum mechanical arguments two different coordinates are introduced for the description of a T1u‐motion of an electronic shell.
Calculation of energy‐dependent photoionization probabilities for valence electrons in diamond and silicon crystals
Authors: Kosakov A. , Unger K. , Leonhardt G. 
Published: July 2007

AbstractPhotoionization probabilities for valence electrons in covalent semiconductor crystals are calculated in order to analyse the connection of the photoelectron spectra with the densities of valence electron states. A model is proposed and tested, which is based on solid state properties (adjusted sp3 tight binding functions and OPW functions are used for the initial and final states, respectively) and which yields purely energy‐dependent photoionization probabilities. Rather good results are obtained for C and Si; discrepancies occurring with Ge are discussed.
Indirect near edge emission in pure AgBr
Authors: Weber J. 
Published: July 2007

AbstractThe emission of pure AgBr single crystals is studied in the vicinity of the indirect band gap from 1.5 to 50 K under various excitation conditions. The spectra are analysed with special respect to properties of the phonons involved in the indirect transitions, the lineshape of the free exciton emission which is found dependent on exciting frequency, and the dependence of some weakly bound exciton lines on temperature and excitation power. Results obtained for a narrow line close to the free exciton emission do not support the proposed model of a recombination of possibly Bose‐Einstein condensed free triplet excitons.
Resonance Raman scattering in a strong electric field
Authors: Bechstedt F. , Enderlein R. , Peuker K. 
Published: July 2007

AbstractA theory is given for the influence of an external electric field on the allowed one‐phonon resonance Raman scattering. It is shown that the phonon peaks of the scattering spectrum remain unbroadened in the presence of the field. The scattering cross section decreases due to the field induced broadening of the stationary electron energies. The relative field induced changes are remarkably large — of the order of magnitude one — if lifetime broadening effects can be neglected. Results for all types of critical points of the electronic transition are presented. It is shown that the field induced change of the scattering cross section decreases strongly if lifetime broadening effects are important. The results provide the theoretical basis for the application of the electromodulation technique to resonance Raman scattering.
Lattice dynamics of paratellurite
Authors: Durand M. , Ayrault B. , Marqueton Y. , Decamps E. A. 
Published: July 2007

AbstractWith infrared reflectivity and Raman scattering all the predicted modes are observed, except one A1 mode. The analysis of the reflectivity spectra leads to low frequency dielectric constants in excellent agreement with those obtained by other authors. The basis vectors of normal modes are determined at several points of the Brillouin zone and these ones of the Γ point compared with those of the rutile structure (SnO2). The unit cell of this last compound is about half of a paratellurite unit cell.
Electrons in finite one‐dimensional crystals in a uniform electric field
Authors: Yang E. 
Published: July 2007

AbstractBy using the time‐dependent Schrödinger equation, the problem of an electron in a one‐dimensional crystal in the presence of a uniform electric field is treated. It is shown that there are two types of electric‐field‐induced energy levels; one is so called Stark ladders and the other is simply due to different boundary conditions. When “appropriate boundary conditions” are imposed on the wave function it is found that the number of periodic potential cells involved in the calculation plays a vital role in determining the existence of Stark ladders. Also, the dynamics of an electron in a one‐dimensional potential well subject to a uniform electric field is studied.
A‐luminescence of alkali halides activated by monovalent mercury‐like ions
Authors: Trinkleb M. F. , Zolovkina I. S. 
Published: July 2007

AbstractPolarization is found of the long‐wave A‐luminescence bands in KI:Tl, KI:In, KBr:In crystals at 7 K. It is established that the dependence of the polarization degree on azimuth corresponds to oscillator emission along the crystal axis [111]. These bands are assumed to be due to “trigonal” Jahn‐Teller minima of the activator 3T1u excited states. It is established that the 400 nm band in KBr:T1 crystal represents emission from the trigonal minimum of the metastable 3A1u‐state of the activator. A doublet structure of the short‐wave A‐luminescence bands is found and investigated. The hypothesis is made that the structure is connected with the presence of two types of tetragonal Jahn‐Teller minima of the activator 3T1u excited states.
Green's function treatment of ordered ternary alloy
Authors: Tahir‐Kheli R. A. 
Published: July 2007

AbstractA Green's function formulation of an ordered ternary alloy is given. The case of a two sub‐lattice system with nearest neighbour pair‐wise, static potentials is studied. A decoupling procedure similar to the molecular field approximation is carried out, and the resultant equations are analysed in detail. Conditions for the ternary order‐disorder transition to be of the second order variety are given, and order parameters are computed for several different potentials and concentrations, for which second order transition occurs. A few remarks concerning possible application of the Green's function method to the study of atomic diffusion and relaxation of spatial order in ternary alloys are also given.
Quantum mechanics of dislocation kinks in covalent semiconductors
Authors: Gosar P. 
Published: July 2007

AbstractA quantum‐mechanical model of the kink motion in covalent semiconductors is presented. A kink is treated as a quasi‐particle which is strongly coupled to the elastic continuum and can move along the dislocation by tunneling between neighbouring equilibrium sites. Kinks are most likely self‐trapped because of the deformation of the lattice. The calculation of the mobility at high temperatures reveals a thermally activated nature of the kink diffusion process.
Interaction of holes with local modes and one and two optical phonons as revealed in M‐I‐silicon tunneling spectra
Authors: von Baltz R. , Urban B. 
Published: July 2007

AbstractThe self‐energy and the density of states for holes in degenerate p‐type silicon are calculated taking into account the interaction with the local mode of the boron acceptor and one and two optical phonons. The current‐voltage characteristics of a MIS tunnel junction is obtained using the transfer Hamiltonian model. Adjusting parameters in d2IdU2 to experimental data the line width of the optical phonon and the effective two phonon deformation potential is obtained. In contrast to other authors, the calculations demonstrate that even a small but energy independent collision time of the carriers has a minor influence on the structures in d2IdU2. The interaction of holes with the local mode is essentially due to silicon atoms vibrating in ‐the neighbourhood of the boron ion.
A perturbed O molecule ion in SrCl2 single crystals EPB results
Authors: de Siebenthal J. M. , Bill H. 
Published: July 2007

AbstractA detailed BPR investigation is reported about a perturbed O molecule ion introduced into SrCl2 single crystals. The O is associated with an alkali cation located on a next nearest neighbour lattice site. The local distortions produced by this alkali ion influence the orientation of the O molecule ion.
The “destructive” fermi resonance
Authors: Chisler E. V. , Davydov V. Yu. , Goncharuk I. N. , Ivanova E. A. 
Published: July 2007

AbstractFor the first time the coupling between the fundamental vibration of a crystal and its second‐order vibrational spectrum is observed which causes, due to the interference of the transition probabilities, the decrease of the intensity of second‐order vibrational spectrum and, in certain cases, its almost full cancellation. The “destructive” Fermi resonance is revealed in the Raman and infrared spectra of sodium nitrite. The energy of the resonance coupling and the unperturbed transition probabilities are calculated. The spectroscopic data show, that the electrooptic parameters of the second‐order vibrations and the energy of their interaction with the fundamental vibration are approximately independent of the wave vector within the Brillouin zone.
Semi‐classical and quantum‐mechanical theory of hopping conduction
Authors: Bányai L. , Aldea A. 
Published: July 2007

AbstractA thorough analysis of the semi‐classical and quantum‐mechanical hopping conduction model is made within the frame of the linear response theory. The approach differs in several respects from the previous ones. A deeper understanding of the conditions under which such a mechanism occurs is achieved from the quantum‐mechanics point of view.
On some possible consequences of exciton‐phonon interaction
Authors: Stojanović S. D. , Šetbajčć J. P. , Škrinjar M. J. , Tošić B. S. 
Published: July 2007

AbstractAn exciton system with strong exciton‐phonon coupling is considered. It is shown that the virtual exchange of phonons leads to an effective exciton‐exciton interaction which cannot cause the creation of biexcitons. However it leads to the formation of exciton drops. The elementary excitations arising in the process of the desintegration of the exciton drops have superfluid properties.
Degenerate hubbard model in a magnetic field. Application to Jahn‐Teller systems
Authors: Khomskii D. I. , Kugel K. I. 
Published: July 2007

AbstractThe Hubbard model in the strong coupling limit is used to study the behaviour of substances containing ions with orbitally degenerate ground state (Jahn‐Teller ions) in a magnetic field. In such substances the orbital occupancy and the magnetic structure appear to be closely connected. It is shown that in these systems a transition of first order may occur between different anti‐ferromagnetic phases as well as jumplike spin‐flip transitions (even for an isotropic exchange interaction SiSj). The field dependence of the magnetic moment may be nonlinear, typical of meta‐magnetic substances. Both a simple model problem and a specific case of pervoskites with Jahn‐Teller ions (such as KCuF3) are studied. The behaviour of quasi one dimensional systems is also considered.
Calculation of the temperature‐dependent DC conductivity of disordered alloys in off‐diagonal CPA
Authors: Kolley E. , Kolley W. 
Published: July 2007

AbstractIn the presence of electron‐phonon interaction the dc conductivity of off‐diagonal random alloys is calculated in a modified CPA including vertex corrections. The numerical conductivity results reflecting realistic features of the model used depend strongly on off‐diagonal randomness and temperature. The combined effect of electron‐phonon scattering and statistical correlations can provide localization of minority‐band states.
Paraelectric resonance of hydrogen bonds in ferroelectries and related phenomena
Authors: Vikhnin V. S. , Gordon A. Ya 
Published: July 2007

AbstractA theoretical consideration is made of paraelectric resonance (PER) of hydrogen bonds (HB) in KH2PO4‐type ferroelectrics. It is shown that the intensity of PER HB essentially increases in the external hydrostatic pressure field. The broadening mechanisms of the PER lineshape are discussed. The properties of the paraelectric phase with the tunneling states of HB, which occur in the high hydrostatic pressure field are studied. Nonresonance investigation methods of such tunneling paraelectric phase, notably the investigations of heat capacity and dielectric permittivity are considered together with the PER.
Electro‐optic properties of CuCl below the absorption edge
Authors: Mohler E. , Thomas B. 
Published: July 2007

AbstractThe dispersion and temperature dependence of the electro‐optic coefficient r of CuCl‐ are measured for wavelengths between 700 nm and the absorption edge near 400 nm. A method is described to eliminate the influence of residual strain birefringence which otherwise leads to serious errors. The dispersion of the optical dielectric constant and the electro‐optic coefficient is used to determine a schematic spectrum of the imaginary part of the dielectric constant and its changes in an external electric field. A model for the lattice contribution to the electro‐optic effect of CuCl based on the concept of bond polarizability is discussed.
Low‐temperature knight‐shift investigations of yttrium metal
Authors: Karcher R. , Lüders K. , Roth G. , Szücs Z. 
Published: July 2007

AbstractThe Y89 NMR is measured in the temperature range from 8 K to room temperature and in magnetic fields up to 80 kG. The Knight shifts KiSO and Kax are determined analysing the lineshapes. At the temperature T = 13 K. Kiso = (0.327 ± 0.005) % and Kax = (0.026 ± 0.002) %. A linear temperature dependence is found for both the Knight shifts: 1 × 104 % K−1 for KISO and 0.1 × 104 % K1 for Kiso. The results are discussed in connection with other electronic properties. It is possible to get a complete separation of the s‐, d‐, and orbital contributions not only for the Knight‐shift but also for the susceptibility and the relaxation rate.
Recombination luminescence in alkali halides doped with monovalent cations. (VK + e)A‐type emission
Authors: Ikeya M. , Crawford J. H. 
Published: July 2007

AbstractTwo types of emission bands are observed in alkali halides doped with monovalent cation impurities during X‐irradiation; Em‐I which is observed at low temperature where the self‐trapped hole, X is immobile and Em‐II, which is observed above the temperature where X becomes mobile. Em‐I is ascribed to(X + e) recombination perturbed by a monovalent cation. Em‐II is associated with ([X]A + e) recombination in which , is trapped by a monovalent cation.
On the influence of disorder on the electron density of states in a simplified model for a quasi‐onedimensional conductor
Authors: Cubiotti G. , Donato E. , Giuliano E. S. , Ruggeri R. 
Published: July 2007

AbstractThe electron density of states and their localization are investigated on a simple model consisting of single platinum chains surrounded by a halogen lattice whose sites are randomly occupied. The values of the hopping integrals are parametrized and, the localization of the states over certain ranges of energy is studied.
Temperature dependence of the electrical conductivity and hall coefficient in 2H‐MoS2, MoSe2, WSe2, and MoTe2
Authors: El‐Mahalawy S. H. , Evans B. L. 
Published: July 2007

AbstractThe electrical conductivity and Hall coefficient perpendicular to the c‐axis of hexagonal MoS2, MoSe2, and WSe2 are measured over the temperature ranges 120 to 1170 K and 140 to 820 K, respectively. The derived temperature‐dependent carrier densities are described by n ∼ exp (–E/kT) for temperatures less than 800 K indicating (thermal) energy gaps of 0.38 eV in n‐type MoS2, 0.27 eV in n‐type MoSe2, and 0.19 eV in p‐type WSe2. Above room temperature the carrier mobilities are given by μ ∼ T−α, where α ≈ 1.5 in MoS2, MoSe2 and 2.7 in WSe2. The high‐temperature (>800 K) thermal activation energies of conduction correspond to energy gaps of 1.27, 0.95, and 1.33 eV in MoS2, MoSe2, and WSe2, respectively. Similar measurements on MoTe2 crystals grown by bromine vapour transport demonstrate the effects of included bromine on the low‐temperature conduction processes.
Screw‐dislocation‐induced scattering processes and acceptor states in Te
Authors: Farvacque J. L. , Douehan J. C. , von Alpen U. , Gmelin E. 
Published: July 2007

AbstractElectronic properties of e‐screw dislocations, introduced by shear experiments, are studied by galvanomagnetic and optical absorption measurements. The experiments clearly establish the existence of induced acceptor levels in the band gap. The origin of the dislocation charge its well as the scattering mechanisms induced by the dislocations are discussed with respect to three possible mechanisms: deformation potential, piezoelectric potential and core effect.
Dispersion of bulk phonon polaritons inside reststrahlen bands
Authors: Schuller E. , Falge H. J. , Borstel G. 
Published: July 2007

AbstractWhen pure spatial damping is taken into account, i.e. when the wave vector is treated as complex and the frequency as a real quantity, dispersion curves of bulk phonon polaritons exhibit turnabouts caused by limiting momenta for the wave vectors which lead to branches within the frequency range of reststrahlen bands. The evaluation of the dispersion curves from reflection experiments for fixed frequency and swept angle of incidence confirms these features. Depending on the experimental arrangement dispersion curves inside of reststrahlen bands are investigated for α‐quartz. The measurements turn out to be a sensitive aid for the determination of damping parameters.
Linear optical anisotropy investigations of the antiferromagnetic phase transition in MnO
Authors: Treindl A. , Germann K. H. 
Published: July 2007

AbstractThe linear optical anisotropy of MnO single crystals is investigated as a function of the wavelength, the magnetic field, and the temperature near the antiferromagnetic phase transition at TN = 118 K. The linear magnetic birefringence (LMB) and the dichroism (LMD) show pronounced structures between 13000 and 22000 cm+1 which decrease with increasing temperature and vanish above TN. They are connected with the 4T1g‐ and 4T2g‐absorption bands of the Mn2+ ions. In the LMB spectra a temperature‐dependent background is associated with the band gap absorption. Magnetic fields up to 7.5 T have no effect on the LMB and LMD. The temperature dependence of the optical anisotropy shows the behaviour of the long‐range order parameter of the phase transition which is discontinuous at TN. An exchange striction model which includes uniaxial stress and magnetic fields is discussed in the mean field approximation; the results are in quantitative agreement with the experimental data.
Inelastic neutron scattering in SbSi near the ferroelectric phase transformation
Authors: Pierrefeu A. , Steigmeier E. F. , Dorner B. 
Published: July 2007

AbstractInelastic neutron studies are performed on SbSI. The (013) Bragg peak intensity is strongly temperature dependent and gives evidence for the first order ferroelectric transition. Experimental reasons (poor statistics, small samples) do not permit conclusions concerning the overdamped and rather broad coupled soft mode‐central peak entity which is observed in light scattering. An underdamped soft mode can be excluded. Acoustic and optical phonon dispersion surfaces are measured around the [0ζ0] direction and polarized in [001], which exhibit deep valleys along [0ζ0]. This correlates well with previous diffuse X‐ray results. The depth of the valleys increases strongly in changing the phase from paraelectric to ferroelectric.