bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calculation of the magnetization–temperature dependence of rare‐earth and yttrium iron garnet solid solutions
Authors: Falileev G. N. 
Published: July 2007

AbstractUsing the known compensation temperature–concentration dependences in the molecular field theory simple expressions for calculating the temperature dependences of the c‐sublattice magnetization and the saturation magnetization for the iron garnet (IG) solid solutions of the Y3–c‐RcFe5O12 (R = Gd, Tb, Dy, Ho, Er, Tm, Yb) type are obtained. The calculated data agree well with the experiment at T ⪆ 150 K. The discrepancy between the calculated data and the experiment at T ⪅ 150 K is due to the rare‐earth ion interaction. The correction for this interaction shows that in IG″ besides the Kramers‐Anderson exchange between the rare‐earth ions there exists an additional exchange interaction like that of the Ruderman‐Kittel‐Kasuya‐Yosida (RKKY) type playing an important role at temperatures lower than “the low temperature” point. The expression is obtained with a correction for interactions between the rare‐earth ions using the experimental magnetization temperature dependence of “pure” rare‐earth IG of the R3Fe5O12 type, which allows the calculation of the magnetization–temperature dependence of IG under investigation including temperatures ⪅ 150 K.
Temperature dependence of atomic core levels in solids II. Chemical shift and relaxation energy of core levels and their dependence on temperature
Authors: Hübner K. , Bechstedt F. 
Published: July 2007

AbstractFor the first time an explicit investigation is made of the T‐dependence of atomic core levels in non‐metallic solids and shown that this dependence can be of the same order as that one of electronic energy bands. The basis for these investigations are models for the chemical and the relaxation shift of core levels, which lead to absolute core‐level energies and their shifts in agreement with corresponding photoemission data. After separation of the T‐dependence of conduction‐band and core‐exciton energies of GaP, Si, and SiO2 (Part I of this work), which is involved in the total T‐dependence of corresponding core‐level to conduction‐band transitions, it is shown in the present part that multiphonon and hydrostatic processes lead to large and different T‐coefficients of the Si2p level in Si and SiO2, whereas the different contributions to the T‐dependence of the Ga3d level in GaP give an almost vanishing total effect. Furthermore, it is shown that the main contributions to the T‐dependence of atomic core levels in semiconductors and insulators come from the electrostatic interaction of the core electrons with their environment, whereas the T‐dependence of relaxation energies is very small. The results are in agreement with data, which are deduced from corresponding experiments performed by Aspnes et al.
The relation between bonding and g‐shift for TI2+ and Pb3+ in alkali halides
Authors: Moreno M. 
Published: July 2007

AbstractThe experimental g‐shift of TI2+: KCl, TI2+ :KBr and Pb3+ :KCl is theoretically analysed within the [ML6] cluster model (M metal ion; L ligand). Though the calculations include up to third‐order contributions in energy (especially important for TI2+ :KBr) and reproduce the sign and the qualitative trends of the experimental g‐shift of the systems studied, a reasonable quantitative agreement with the observed g‐shift is, however, only reached for TI2+ :KCl.
Interatomic potentials from experimental phonon spectra II. General results
Authors: Swaroop A. , Esterling D. M. 
Published: July 2007

AbstractA method described in the previous paper to extract interatomic potentials from phonon spectra is applied to a variety of simple, noble, and transition metals. The interatomic pair potentials for Rb, Pb, Ag, Au, Cr, Mo, W, V, Nb, Ta, Ni, Pd, and Pt are reported and discussed in the light of other available potentials.
AC Conductivity and dielectric anomaly in annealed EuSe
Authors: Kuivalainen P. , Kaski K. , Eränen S. , Stubb T. , Stubb H. 
Published: July 2007

AbstractThe complex permittivity of annealed n‐type EuSe is measured in the temperature range T = 4.2 to 295 K for frequencies 103 to 2.4 × 1010 Hz. Using further the results of the crystallographic characterization and the dc conductivity σdc, Hall effect, and optical transmittance measurements one finds that shallow donors associated with Se vacancies and a decrease in their concentration due to annealing can explain the T and annealing dependences of σdc and σac. At T = 295 K where σdc is high, no frequency dispersion of σac is found even at microwave frequencies. When σdc decreases drastically at low temperatures a strong frequency dependence of σac is seen. It follows the relation for ac impurity hopping conduction proposed by Pollak: σac ⋐ ωs with s < 1 at low frequencies and 1 < s ≦ 2 at high frequencies. A maximum hopping frequency τ−1 = 4.0 × 109 s−1 and an average hopping length R = 9 Å at low temperatures is estimated. The annealing dependence of the dielectric constant at low temperatures can be explained by the polarizability αd of neutral Se vacancies. From the measured αd = 3.2 × 106 Å3 the carrier effective mass m* = 0.28 is estimated.
Mode damping by electrostrictive interaction in a uniaxial ferroelectric
Authors: Roy G. K. , Das A. N. 
Published: July 2007

AbstractAn electrostrictive‐type coupling model is used to study mode damping in the paraelectric phase of a uniaxial ferroelectric with an anisotropic soft‐mode dispersion. Mode linewidths are obtained by solving the phonon Green's function equation of motion in the self‐consistent phonon approximation (SPA). The dominant contribution to the damping comes from the scattering of a soft optic phonon with the absorption or emission of an acoustic phonon. The soft‐mode damping γs shows a (T – T0)1/2 behaviour while, in the isotropic limit, it becomes linearly dependent on temperature. For large anisotropy, the longitudinal acoustic attenuation α1 ∝ ω2(T – T0)−1/2X XIn (T – T0)−1/2 or ω2(T – T0)−1/2 according as the soft‐mode is under or over‐damped in the opposite limit, the corresponding dependences are ω2(T – T0)−1/2 and ω2(T – T0)−3/2, respectively. If soft‐mode interaction with other modes (e.g. phonon density fluctuations) are considered, γs becomes nearly temperature‐independent in this case α1 behaves like ω2 (T – T0)−1 which compares favourably with experimental observations on lead germanate where the soft‐mode is overdamped.
EPR studies of VO2+ ions in rochelle salt crystal
Authors: Kulliński W. J. , Hoffmann S. K. , Więckowski A. B. 
Published: July 2007

AbstractEPR results for vanadyl ion doped Rochelle salt are reported. Impurity sites in the unit cell, and the molecular structure of the VO(tartrate)2 complex in the crystal are found and the spin‐Hamiltonian parameters are determined at room temperature. A considerable non‐axiality of the g and A tensors and the MO bonding coefficients are discussed. The EPR spectra are not affected by the phase transitions.
Model for local moments in a spin density wave host
Authors: Moyer C. A. , Kelly J. R. , Arajs S. 
Published: July 2007

AbstractAn effective spin Hamiltonian is obtained for a system of impurity spins embedded in an itinerant electron antiferromagnetic matrix. Each spin couples to the polarization field of the spin density wave (SDW) via a d–d exchange interaction with the conduction electrons. The impurity spins also interact among themselves via modulation of the conduction electron spin polarization. Using the two‐band model for antiferromagnetism in chromium, it is possible to obtain closed forms analogous to the RKKY result for the spin–spin and spin–matrix interactions. A general effect of SDW formation is to reduce the spin–spin coupling strength, since some conduction electrons are “tied up” in the SDW and are no longer free to mediate the interaction. The SDW is also responsible for the appearance of an antisymmetric interaction which favors canted spin arrangements.
Long‐range many‐body interaction and monovacancy heat of formation of rare‐gas crystals
Authors: Maity S. N. , Roy D. , Sengupta S. 
Published: July 2007

AbstractThe heat of formation of rare gas crystals is calculated using a relatively simple approach. As the difference in the values of heat of formation and cohesive energy depend entirely upon the relaxation and many‐body effects, the contribution of these terms to the heat of formation is examined critically. It is found that the relaxation effect is quite negligible. Though three‐body interaction other than triple‐dipole approximately cancels with the higher many‐body effects in the case of cohesive energy, the cancellation is not at all complete in the case of heat of formation, and the many‐body effects other than the triple‐dipole is found to contribute significantly to the difference between the energy of the perfect and imperfect crystal. The differences in the values of heat of formation and cohesive energy are calculated for the rare gas solids using a very simple approach and compared with experimental results and also with those obtained from more sophisticated calculation. The present calculation is found to reasonably reproduce the experimental results. It is emphasised that an accurate determination of this difference is necessary as this serves as a direct test of the role of many‐body forces in rare gas solids.
On Kinetic Exchange Theory
Authors: Eremin M. V. , Rakitin Yu. V. 
Published: July 2007

AbstractThe kinetic exchange in transition metal ion pairs is analyzed for the case of crystal fields of simply reducible symmetry groups. The effects of non‐orthogonality of molecular orbitals belonging to different centres are treated explicitly for the first time in the multi‐electron theory. The kinetic exchange parameters are related to the covalency parameters of the metal—metal “bond” and charge transfer energies. The particular cases of low and high charge transfer energies are considered. It is shown that with low charge transfer energies, strong ferromagnetic kinetic exchange may predominate. Certain differences in the operator forms of the direct and kinetic exchange Hamiltonians are discussed. The results obtained are applied to interpret experimental data.
Scattering of Photons by Channeled Particles
Authors: Bazylev V. A. , Zhevago N. K. 
Published: July 2007

AbstractThe theory of spontaneous and induced resonance scattering of photons by relativistic channeled electrons is developed. The coefficient of enhancement of the scattered radiation is calculated. It is shown that the population of the transverse energy levels of a channeled particle can be effectively changed with the help of modern lasers.
Investigation of the Crystal Field in PrNi5
Authors: Alekseev P. A. , Andreeff A. , Griessmann H. , Kaun L. P. , Lippold B. , Matz W. , Sadikov I. P. , Chistyakov O. D. , Markova I. A. , Savitskii E. M. 
Published: July 2007

AbstractInelastic slow‐neutron scattering experiments are made on polycrystalline samples of intermetallic compounds PrNi5 and LaNi5 over the temperature range 8 to 295 K. The peaks of the inelastic magnetic‐neutron—rare‐earth‐ion scattering resulting from the splitting of the ion ground state into a number of levels by the crystal electric field (CEF) of hexagonal symmetry are identified by temperature and angular dependence of resonance intensities and by comparing PrNi5 spectra with those of LaNi5. On the basis of an effective point charge model for the CEF Hamiltonian with four variable parameters, calculations are made and CEF level scheme is restored. Magnetic contributions to the temperature dependence of heat capacity and magnetic susceptibility of PrNi5 are calculated and compared with available experimental data.
EPR of Hydrogen and Deuterium Atoms in Alkali Halide Crystals
Authors: Badalyan A. G. , Baranov P. G. 
Published: July 2007

AbstractIn RbCl, KBr, and NaCl crystals EPR spectra of anion atoms of hydrogen (H) and deuterium (D) are obtained and studied after UV irradiation. Hyperfine structure constants and g‐factors of H and D centres are determined from these spectra. In RbCl resolved structure of the EPR lines of H and D is observed in the orientation H ‖ [100]. The atoms H and D are supposed to occupy off‐centre positions in crystals.
Radiative Recombination at Donors and Acceptors. Averaging over the Configuration of Majority Impurities
Authors: Paasch G. , Christke E. , Kausch M. 
Published: July 2007

AbstractFor the determination of the radiative recombination the configurational average for the majority impurities is calculated taking into account that the impurities fall on discrete sites. This gives only slight changes for the stationary behaviour in comparison with a completely random distribution while the kinetics is more affected. In addition the initial decay rate is examined.
ENDOR Study of the F‐Center in KMgF3
Authors: DuVarney R. C. , Niklas J. R. , Spaeth J. M. 
Published: July 2007

AbstractWith ENDOR the superhyperfine (shf) interactions of the F‐center electron in KMgF3 with neighboring nuclei are measured out to the tenth shell. Using ENDOR‐induced ESR it could be established that the shf interactions of the next‐nearest F‐neighbors along the tetragonal axis are bigger roughly by a factor of two than those in the perpendicular plane. The other shells also reflect the tetragonal symmetry of the site. The g‐factor, however, is isotropic with g = 1.9983 ± 0.0005.
Optical Properties of Molybdenum by Electron Energy Loss Spectroscopy
Authors: Manzke R. 
Published: July 2007

AbstractThe energy loss function Im (−1/ϵ(ΔE)) of polycrystalline Mo films is determined by electron energy loss experiments in transmission with 56 keV electrons. By means of Kramers‐Kronig analysis the complex dielectric function ϵ = ϵ1 + iϵ2 and the reflectivity R(ΔE) are calculated in the energy range from 1.5 to 38 eV. The results are compared with those obtained from optical reflectance data.
Activation Volume for Vacancy Motion in Calcium Fluoride
Authors: Fontanella J. J. , Wintersgill M. C. , Andeen C. 
Published: July 2007

AbstractThe audio frequency complex dielectric constant for sodium doped calcium fluoride is measured at pressures up to 0.4 GPa over the temperature range 240 to 270 K and at zero pressure over the temperature range 5.5 to 400 K. Consequently, the reorientation of a nearest‐neighbor vacancy around a substitutional sodium ion is studied. The activation volume for the motion is found to be (1.73 ± 0.1) cm3/mol. It is argued that this value should be similar to the migration volume for “free” vacancies. The compressibility of the activation volume is found to be forty times the compressibility of the host lattice. Finally, a large negative thermal expansion coefficient is found for the activation volume for vacancy motion.
The Scattering and Recombination of Coherent Excitons in Molecular Crystals
Authors: Ivanov G. K. , Kozhushner M. A. 
Published: July 2007

AbstractThe elastic and inelastic exciton—exciton scattering is regarded. Exact expressions for the scattering matrix are obtained in the long‐wave approximation for any molecular crystal. Calculations for the exciton—exciton scattering in anthracene are carried out and two possible values for the dynamical interaction between excitons are obtained by using the experimental data on the nonlinear fluorescence quenching of excitons.
EPR of Mn2+ and VO2+ in K2C2O4 · H2O Single Crystals
Authors: Jain V. K. 
Published: July 2007

AbstractThe electron paramagnetic resonance spectra of Mn2+ and VO2+ impurities in K2C2O4 · H2O are analysed in X‐band at 298 K. The ions do not appear to enter the lattice as substitutional impurites. The double separation of forbidden hyperfine transitions (Δm = ± 1) are studied in Mn2+ doped crystals. It is found that the different parts of the single crystals are characterized by different intensity ratios of two magnetically inequivalent complexes. This behaviour is prominent in VO2+ doped crystals.
The Entropy of Internal Stress Fields
Authors: Schoeck G. 
Published: July 2007

AbstractIn the strictly linear elasticity theory (no third order terms in the expansion of the free energy) or in the harmonic approximation for a crystal, there is no entropy change when an internal stress field is introduced into a body. When higher order terms are considered it is shown that in the expressions given by Zener and DiMelfi et al. terms are missing which in the hierarchy of perturbation are of the same order however due to the magnitude of the material parameters generally make a small contribution. In addition there exists an entropy of interaction between two internal stress sources.
Short‐Range Magnetic Order in a Disordered Ising Ferromagnet
Authors: Medvedev M. V. , Goryainova S. M. 
Published: July 2007

AbstractIn the molecular field approximation it is shown that in an Ising magnet with nearest‐neighbour random exchange bonds, both the long‐range ferromagnetic order and a short‐range magnetic one appear at the transition from the paramagnetic state into the random ferromagnetic one. The two‐point two‐spin correlation function of the short‐range magnetic order falls off like R−1on at large distances Ron ≫ a (a is the lattice spacing).
Calculation of Jahn‐Teller Coupling Constants of 3d Transition metal Ions in Crystals. I. General Theory
Authors: Nikiforov A. E. , Shashkin S. Yu. , Krotkii A. I. 
Published: July 2007

AbstractA method is proposed for the calculation of the Jahn‐Teller coupling constants for orbitally degenerated states of ions in crystals based on the application of perturbation theory in adiabatic potential matrix calculation. The cluster approximation and LCAO‐MO scheme are used.
A General Pseudopotential Approach to Metallic Compressibilities
Authors: Kachhava C. M. , Sharma K. S. 
Published: July 2007

AbstractA general theory for the binding energy and compressibility of metals applicable to any form of model pseudopotentials is presented. The usual contributions of the electrostatic, kinetic, exchange, correlation, and Hartree terms to the binding in metals are considered in the formulation. The band‐structure part is explicitly worked out using a general pseudopotential in conjunction with the Hartree dielectric screening. The formula so obtained for the compressibility is then specialized for the case of linear model potential and tested on eight metals. A good agreement between the theory and the experiment justifies the formulation based on the second order perturbation theory. Qualitative improvements are observed on using the self‐consistent screening.
Boundaries of Metastable States in type II Superconductors
Authors: Shehata L. N. 
Published: July 2007

AbstractFor a cylindrical type‐II superconductor in an external magnetic field H0 parallel to the sample surface the values are calculated for the critical exit field Hex(B) where a flux‐vacancy may be formed in the layer of vortices nearest to the surface and the critical entry field Hen(B) where a new flux layer may be formed. The interaction of vortex lines with large‐scale surface distortions is also considered and shows a decrease in the value of the penetrating field in agreement with experimental results.
Electrical Resistivity of Polyvalent Liquid Metals by Harmonic Model Potential
Authors: Sahay B. B. , Srivastava P. L. , Mitra N. R. 
Published: July 2007

AbstractA parabolic form of potential in place of a constant potential (Heine‐Abarenkov type) inside the ion core region is considered. The form has the advantage of reducing the difference between the potential gradients at the model radius. Its effect on electrical resistivity of liquid Zn, Cd, Hg, In, Tl, and Pb is investigated. The results show positive influence in all cases except Hg.
Critical Temperatures of the Random Heisenberg‐Ising Magnets Amorphous Magnets and Spin Glasses in the Binary Mixtures
Authors: Katsura S. , Shimada K. 
Published: July 2007

AbstractThe Curie temperature of the amorphous Heisenberg‐Ising ferromagnets with random distribution of exchange integrals, and the Curie, the Neél, and the spin glass transition temperatures of binary mixture of the ferro‐ and the antiferromagnetic bonds in the Heisenberg‐Ising magnets are calculated. Similarity and difference between the Heisenberg‐Ising models and Ising models are clarified.
On the Direct Interaction Between Impurities in the Anderson Model
Authors: Zieliński J. 
Published: July 2007

AbstractThe method of functional derivatives is used in the problem of two interacting impurities. The symmetric Anderson model is considered and the prescription for generating diagrams for the selfenergy and the magnetic susceptibility of localized d‐electrons is given. Correspondence is found with the case of an isolated impurity. The temperature variation of the electrical resistivity and magnetic susceptibility is presented and the physical mechanism are discussed.
Energy Band Structure and Bloch Functions in the Planar Channeling Model with the Kronig‐Penney Potential
Authors: Babakhanyan E. A. , Kononets Yu. V. 
Published: July 2007

AbstractThe motion of a charged particle in a one‐dimensional periodic potential of the Kronig‐Penney type is considered. The energy band structure, Bloch wave functions (BWF) in coordinate and momentum representation are investigated in detail. Two sharply distinguished groups of states, i.e. below‐barrier and above‐barrier, are extracted and the role of both of them in the channeling of positively and negatively charged particles is explained. It is shown that only using a dispersion equation form one is able to obtain information on the symmetry properties of the BWF at the edges of energy bands. An estimate of the corresponding regions of the edge coherence in the Brillouin zone is given. In the above‐barrier case a nontrivial effect is found of parity interchange violation of the BWF at the edges of energy bands, connected with the nullification of the reflection coefficient either from the single barrier or well. An oscillatory behaviour of both allowed and forbidden band widths is revealed. The analytical results for different values of the parameters are illustrated by computer calculations.
Anisotropy of Spin Splitting and the Band Structure Parameters of HgSe from Shubnikov‐De Haas Experiments
Authors: Gałązka R. R. , Dobrowolski W. , Thuillier J. C. 
Published: July 2007

AbstractMeasurements are made of the Shubnikov‐de Haas (SdH) effect at 4.2 K up to 180 kOe in HgSe samples with electron concentration in the range 1.7 × 1017 to 2.2 × 1018 cm−3. The theoretical analysis is based on the Pidgeon and Brown model. The spin splitting of SdH oscillations shows an angular dependence. The anisotropy of the spin splitting exceeds 15% between < 100 > and < 111 > direction and depends on energy and the quantum number of the Landau levels. The theory gives satisfactory agreement with the experimental data. A new set of band structure parameters is established. Additional peaks in SdH oscillations, which are not predicted by the model, are also observed.
Spin Waves in Amorphous Antiferromagnets
Authors: Bogomaz I. V. , Ignatchenko V. A. , Iskhakov R. S. 
Published: July 2007

AbstractThe modifications of the dispersion relation of the spin waves are calculated using two methods: the discrete method for the lattice model with exchange integral fluctuations in the form of δ‐correlated “white noise” and the phenomenological method for the continuous model with arbitrary correlation ranges of the fluctuations of the exchange parameters 1/k0. A change in the character of the dispersion law ω(k) occurs in the vicinity of the point k ≈ k0/2. The results which are obtained by these methods coincide in the long‐waves limit (at k<π/a and k ≪ k0/2, respectively).