bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Phonon Spectrum of Sodium Bromate by Laser Raman Spectroscopy
Authors: d'Andrea A. , Fornari B. , Mattei G. , Pagannone M. , Scrocco M. 
Published: July 2007

AbstractThe optical phonon spectrum of NaBrO3 has been determined by Raman scattering. Comparison with the infrared reflection spectra reported in literature is made. Good agreement is found between the two kinds of measurements. From the polar phonon frequencies a value of 5.63 is calculated for the static dielectric constant, whose experimental value is reported to be 5.7. Dielectric transition strengths and damping constants are also determined from the Raman data.
The Contribution of the Dislocation Forest to the Flow Stress
Authors: Schoeck G. , Frydman R. 
Published: July 2007

AbstractThe formation of junctions between a moving dislocation and the trees of a dislocation forest has been calculated for f.c.c. crystals. In contrast to previous estimates the concept of the orientation‐dependent line energy and a more realistic averaging procedure was used. In a random forest in which the tree length is equal to the tree separation only about 20% of the trees form junctions. The stress to overcome the junctions is higher for screw dislocations than for edges but the exact values depend on the nature of the forest.
A Model Calculation of Optical Absorption in Transition Metals
Authors: Kutty A. P. G. , Manohar C. 
Published: July 2007

AbstractUsing a model Hamiltonian containing a s‐band, d‐band, and s‐d hybridization the optical absorption in the Hartree‐Fock approximation is calculated. It is also shown that RPA corrections to optical absorptions are negligible as long as the s‐band is free‐electron like.
NMR and Susceptibilities of CeAlx Intermetallic Compounds
Authors: Niculescu V. , Pop I. , Rosenberg M. 
Published: July 2007

AbstractNMR and magnetic susceptibility of CeAlx intermetallic compounds with x = 1, 2, 3, and 4 were investigated. The most important contributions to the magnetic susceptibility are the Curie‐Weiss term, expressing the paramagnetism of the localized f‐electrons and the temperature independent term due to an enhanced Pauli paramagnetism, the enhancement factor increasing exponentially with the cerium concentration. The temperature dependence of the observed strong positive Knight shift is explained by the enhancement of the hyperfine interaction at the Al27 sites, owing to the exchange polarization of the conduction electrons by the localized cerium f‐electrons. The exchange constants Jfs and θp are negative for the four investigated compounds. A positive sign of the sum results which characterizes the oscillating behaviour of the indirect exchange interaction between the rare‐earth ions.
Effect of Trigonal Warping on Landau Levels of Graphite
Authors: Gupta O. P. , Wallace P. R. 
Published: July 2007

AbstractWe have devised a successive approximation scheme for taking account of the trigonal warping (γ3) terms in the calculation of the lower‐lying magnetic levels of graphite at fields ⩾ 20 kG. A two‐component effective Hamiltonian has been introduced for these levels. Starting from analytic expressions in the case γ;3 = 0, straightforward and simple iteration schemes have been devised (i) to take account of the higher levels and (ii) to obtain the γ3 contributions. It is found that the trigonal warping changes the levels only by a few per cent except for the n = 0 levels. The levels n = 0, 1, 2, 3 have been calculated for a range of fields from 20 to 200 kG.
Photoemission Studies of Electronic Colour Centres in Additively Coloured KCl and KBr Crystals
Authors: Kashkai A. D. , Berezin A. A. , Arseneva‐Geil A. N. , Matveev M. S. 
Published: July 2007

AbstractThe spectral distribution of the optical absorption and the photoemission quantum yield and the energy distribution of the photoelectrons are studied in the range of the photon energies of 2.0 up to 5.5 eV on additively coloured KCl and KBr single crystals with a concentration of F‐centres of 1017 up to 1018 cm−3. Several energy levels in the forbidden band, responsible for the photoemission, are found. The positions of these levels in respect to the vacuum level are 2.8, 2.5, and 2.1 eV for KCl and 2.9, 2.3, and 1.7 eV for KBr. These levels are supposed to correspond to the ground states of F‐, M‐, R‐electronic colour centres. The above energy values are compared with the theoretical values of the ionization potential of F‐, M‐, and R‐centres calculated in the quasimolecular model of F‐aggregate colour centres. The calculated first ionization potentials, as well as the experimental energy values, decrease when the electronic colour centre became more complex. In KBr crystals an additional energy level 1.4eV below the vacuum level is found which probably corresponds to the N‐centre.
Mechanische Nachwirkung in Kupfer und Nickel, verursacht durch Hantel‐Zwischengitteratome
Authors: Wanger F. J. 
Published: July 2007

AbstractMit Hilfe eines Torsionspendels wurde die Nachwirkung des Elastizitätsmoduls nach plastischer Verformung an Cu und Ni gemessen. Die mechanische Nachwirkung wird durch die beim Verformen erzeugten Hantel‐Zwischengitteratome verursacht, welche im Spannungsfeld einer Versetzung zu einer versetzungsinduzierten Umorientierung (Orientierungsnachwirkung) und Diffusion (Diffusionsnachwirkung) angeregt werden. Aus der Orientierungsnachwirkung ergibt sich die Aktivierungsenergie für die Umorientierung der Hantel‐Zwischengitteratome im Fall von Cu zu 0,67 eV und für Ni zu 0,87 eV. Die Wanderungsenergie der Zwischengitteratome folgt aus der Diffusionsnachwirkung und beträgt für Cu ebenfalls 0,67 eV, für Ni hingegen 0,99 eV. Die Ergebnisse der mechanischen Nachwirkungsmessungen sind in voller Übereinstimmung mit den Resultaten aus inneren Reibungsund magnetischen Nachwirkungsmessungen.
Raman‐and Infrared Reflection Spectra of KBrO3 Single Crystals
Authors: Unger B. , Haussühl S. 
Published: July 2007

AbstractDetailed Raman‐scattering and polarized infrared reflection measurements are reported on KBrO3 at 300 K and at liquid helium temperature. The angular dispersion of all extraordinary phonons is compared with theory. Also the static dielectric constants are determined from the measured frequencies.
The E(k) Relation for a Two‐Band Scheme of Semiconductors and the Application to the Metal‐Semiconductor Contact
Authors: Flietner H. 
Published: July 2007

AbstractThe E(k) behaviour is calculated for a two‐band scheme as an approximation for the vicinity of the forbidden gap of a semiconductor. An estimate is given for the validity of the effective mass approximation in the forbidden gap. Application is made to the metal‐semiconductor contact and it is shown that this model describes the experiments for semiconductors ranging from covalent to the ionic type.
On the Investigation of Small Dislocation Loops in Cubic Crystals by Diffuse X‐Ray Scattering
Authors: Trinkaus H. 
Published: July 2007

AbstractResults for analysing point defects in cubic crystals by diffuse X‐ray scattering as given in a previous paper are applied to small dislocation loops. The scattering pattern in the immediate vicinity of Bragg reflections is shown to indicate whether or not the crystal contains predominantly one of several high symmetry configurations. In the presence of dislocation loops with a lower symmetry or of a mixture of different configurations, average fractions of edge‐ and shear‐components can still be determined. The corresponding parameters also give information about the shape of defects in the case of other types of defect clusters.
Spectroscopic Properties of TbAsO4
Authors: Wüchner W. , Bohm W. , Kahle H. G. , Kasten A. , Laugsch J. 
Published: July 2007

AbstractAbsorption spectra of Tb3+ in TbAsO4, indicate that this material undergoes a Jahn‐Teller induced phase transition from tetragonal to a lower, probably orthorhombic, symmetry at TD = (25.5 ± 2.5) K. Zeeman spectra with the magnetic field in the basal plane taken below TD, show a large anisotropy which is caused not only by the g‐factor but also by large internal fields. The g‐tensor of the isolated two lowest singlets, which are separated less than 0.6 cm−1 at 1.74 K, is uniaxial with g110 = 17.0 ± 1.0 in the [110] direction. Measurements down to 0.77 K show a magnetic phase transition at TN, = (1.48 ± 0.04) K to an antiferromagnetically ordered state which increases the splitting of the two lowest lying singlets up to (2.62 ± 0.06) cm−1 at 0.77 K.
Covalency and Deformability of Ag+‐Ions in the Lattice Dynamics of Silver Halides
Authors: Fischer K. , Bilz H. , Haberkorn R. , Weber W. 
Published: July 2007

AbstractThe lattice vibrations of the silver halides AgCl and AgBr have been investigated using a shell model with deformable ions. The deformability of the d‐shell of the Ag+‐ion and its covalent coupling to the neighbours have been considered by introducing two new degrees of freedom in the electronic shell of the Ag+‐ion. They are of quadrupolar (Γ12+) and of rotational (Γ15+) symmetry character. The calculations have been confirmed by comparison with the unpolarized Raman spectra of second order.
Magneto‐Optical Spectra Due to Excitons in Cuprous Halides
Authors: Suga S. , Koda T. , Mitani T. 
Published: July 2007

AbstractFaraday rotation and magnetic circular dichroism spectra have been investigated in the exciton absorption region of CuCl, CuBr, and their solid solutions. The characteristic temperature dependence of the observed spectra is successfully interpreted in terms of the mixing effect of the Z3 and Z1,2 excitons caused by the magnetic field.
On the Theory of Nonradiative Transitions in Polar Media II. Processes with “Nixing” of Quantum and Classical Degrees of Freedom
Authors: Dogonadze R. R. , Kuznetsov A. M. , Vorotyntsev M. A. 
Published: July 2007

AbstractThe probability of radiationless transition between two multidimensional parabolic terms is calculated for the processes with “mixing” of quantum and classical degrees of freedom. The dependence of the transition probability on the heat of the process is investigated. The transition is shown to be of quasi‐activation less and quasi‐barrier less character at large values (modulo) of the heat of the process.
Mechanische Nachwirkung durch induzierten Snoek‐Effekt
Authors: Hornung W. 
Published: July 2007

AbstractFür kubisch‐flächenzentrierte Metalle wird die mechanische Nachwirkung aufgrund weitreichender Wechselwirkung zwischen Versetzungen und Zwischengitteratomen in der Hantellage (ZGA) berechnet. In Übereinstimmung mit Experimenten von Wagner ergeben sich zwei Anteile im zeitlichen Verlauf von Moduldefekt und Dämpfung, von denen der eine mit der Umorientierung der ZGA in homogenen Spannungsfeldern, der zweite mit den bei der weitreichenden Diffusion auftretenden Wanderungsschritten verknüpft ist. Dies erklärt das unterschiedliche Verhalten von Kupfer und Nickel in solchen Experimenten.
On the Verwey Transition in Magnetite
Authors: Lorenz B. , Ihle D. 
Published: July 2007

AbstractThe Verwey transition in magnetite is investigated using a band model with interatomic Coulomb energy introduced by Cullen and Callen. This model is treated in the Hartree‐Fock approximation. A tight‐binding calculation of the band structure with Verwey ordering yields a gap in the single‐particle excitation spectrum for M = (U/2|h|) m > 1 (U Coulomb energy, h overlap integral, m ordering parameter). Below the Verwey temperature Tv semiconducting behaviour for M > 1 and a region of gapless Verwey ordering and semimetallic behaviour for 0 < M ⩽ 1 is found.
On the Theory of Parametric Excitation of Magnetostatic Modes in Infinite Ferromagnetic Plates by Parallel Pumping
Authors: Dintner H. , Klupsch Th. 
Published: July 2007

AbstractBased on the conception of a generalized Polder tensor, the Damon‐Eshbach theory of magnetostatic modes propagating in infinite ferromagnetic plates magnetized parallel to the surfaces is extended including a microwave field parallel to the de field. Restricting to modes obeying the parametric resonance condition, a set of equations determining the mode parameters is derived which exhibit the description of instabilities. The critical microwave field strength hc, for setting‐in the instability with respect to the whole system is calculated for X‐band pump frequencies within the volume mode region using YIG material parameters by introducing a phenomenological damping constant. hc, plotted over the static field strength (“butterfly curve”) appears as a smooth curve because of a favoured excitation of modes situated within a quasi‐continuous part of the spectrum. The possibility of an excitation of surface modes with high pumping efficiencies is suggested.
Spectroscopic Confirmation of a Crystallographic Phase Transition and of Antiferromagnetic Ordering in TbPO4
Authors: Böhm W. , Herb R. , Kahle H. G. , Kasten A. , Laugsch J. , Wüchner W. 
Published: July 2007

AbstractThe optical absorption spectrum of Tb3+ in TbPO4, shows that this substance undergoes a crystallographic phase transition from tetragonal to some lower symmetry at TD = (3.7 ± 0.5) K. This phase transition lifts the symmetry allowed degeneracy of the lowest lying crystal field component. A magnetic field applied parallel to the optical axis cancels the crystallographic distortion. Below TD = (2.15 ± 0.10) K TbPO4, orders antiferromagnetically with the magnetic moments neither parallel nor perpendicular to the optical axis. An induced magnetism is required for this ordering. The spectroscopic measurements indicate that this magnetic transition should be of first order.
Spin Configuration and Intrinsic Coercive Field of Narrow Domain Walls in Co5R‐Compounds
Authors: Hilzinger H. R. , Kronmüller H. 
Published: July 2007

AbstractIn ferromagnetic materials with large anisotropy constants (K1 > 108 erg/cm3) the domain wall width, δB, is of the order of magnitude of a few lattice constants (10 to 30 Å). The spin configuration of such 180°‐walls in Co5R‐compounds is determined within the framework of the Heisenberg model. It is found that the deviations from the micromagnetic solution occur mainly in the centre of the wall. The wall energy was found to depend periodically on the position of the wall centre with respect to the crystal lattice. The oscillations of the wall energy give rise to a coercive field Hc = const (A/D) exp [– π δB/D] (A exchange constant, D wavelength perpendicular to the domain wall). The possibilities to obtain large intrinsic coercive fields are discussed in some detail.
Constant Coupling Approximation for Amorphous Magnets
Authors: Kobe S. , Handrich K. 
Published: July 2007

AbstractThe constant coupling approximation is used to determine the critical temperatures of amorphous ferro‐ and antiferromagnets, for both the Heisenberg and Ising model. Due to the structure fluctuations of the exchange integrals a decrease of the Curie temperature and the Néel temperature, respectively, are found in comparison with the corresponding crystalline case. This result agrees qualitatively with results of both the Green's function and the high‐temperature expansion treatments.
Determination of the Dielectric Tensor of Pyrene (C16H10) by Means of Electron Energy Loss Measurements
Authors: Venghaus H. 
Published: July 2007

AbstractElectron energy loss spectra from 0 to 40 eV were taken on pyrene single crystals with 60 keV electrons. The energy loss functions Im (−1/εii) (i = x, y, z) were derived from spectra recorded with different orientation of the momentum transferred to the crystal by the electrons scattered inelastically. By means of a Kramers‐Kronig transformation the main axis elements εii of the dielectric tensor were calculated from Im (−1/εii). The results obtained are interpreted in terms of excited molecular states in relation to the results of optical absorption measurements, theoretical work and other electron energy loss experiments.
An EPR Study of a Neutral Manganese Center in NaCl
Authors: Ikeya M. 
Published: July 2007

AbstractAn EPR study of the MnO‐E center below room temperature was made in X‐irradiated and F‐bleached NaCl. In addition to the isotropic spectrum with g = 2.0018 and A = 19.5 × 10−4 cm−1 at room temperature, the spectrum at low temperature shows fine structures with an axial field of D = 160 × 10−4 cm−1 and 〈110〉 and 〈111〉 symmetries, which were analyzed from the shift of (M8 = 1/2 ⇋ M8 = −1/2) transitions. The temperature dependence of the hyperfine coupling constant shows anomalies. These results were discussed based on the assumption that the center is an off‐center.
Fluorine Self‐Diffusion in Pure and Doped CdF2
Authors: Süptitz P. , Brink E. , Becker D. 
Published: July 2007

AbstractUsing F 18 as tracer the fluorine diffusion is measured in single crystals of CdF2, undoped and doped with Na+ or La3+, in the temperature region 270 to 640 °C. The results are discussed with respect to the disorder and the attainable conversion of CdF2 from an insulator to a semiconductor. The fluorine diffusion is large compared with the cation diffusion. Its dependence on doping is characteristic of Frenkel disorder in the anion sublattice, whereby the fluorine vacancies are more mobile than the fluorine interstitials. From the temperature dependence of the diffusion coefficient follows a value of 0.39 eV for the activation enthalpy of motion of fluorine vacancies and 2.1 eV for the formation enthalpy of a Frenkel pair.
The Spectrum of Optical Absorption by Mott Excitons in an Electric Field
Authors: Monozon B. S. , Seysyan R. P. , Shelekhin Yu. L. 
Published: July 2007

AbstractThe wave functions of a Coulomb particle in a weak uniform electric field are obtained by the method of reference problems. Expressions are given for polarized light absorption coefficients for the yellow excitonic series of cuprous oxide. Field dependence of line intensities is established for field induced lines and those allowed in the absence of field. The spectrum was taken of the yellow excitonic series of Cu2O in the electric field at T = 4.2 °K as well as the differential spectrum of this series which was due to the difference in absorption of light polarized in the parallel and perpendicular direction to the electric field. Theory and experiment are in good agreement.
Hole g‐Factor in Sn‐Doped Bismuth
Authors: Giura M. , Marcon R. , Marietti P. , Presutti E. 
Published: July 2007

AbstractA new method for the measurement of the g‐factor is presented. This gives a more detailed knowledge of the hole dispersion law in Sn‐doped Bi and allows to explain some experimental results obtained by Bate et al. A feature of the method is the possibility of determining whether the Landau level splitting is larger or smaller than the spin splitting.
Directional Dependence of Extraordinary Infrared Oscillator Parameters of Uniaxial Crystals (II)
Authors: Lamprecht G. , Merten L. 
Published: July 2007

AbstractThe classical dispersion equation for the extraordinary IR spectrum of uniaxial crystals is shown to be valid, even if damping is included. The directional dependence of the damping factors γj(ϑ) and their effect on the other oscillator parameters (dispersion frequencies ωj(ϑ), oscillator strengths 4 πσj(ϑ) is investigated in detail. Evidence is given for the validity of a sum rule of damping factors. The theory is applied to MgF2, ZnF2 and α‐quartz.
A Closed Formula for Nuclear Quadrupole Relaxation in Ionic Crystals
Authors: Pietilä A. 
Published: July 2007

AbstractIn the harmonic approximation of lattice dynamics, a closed formula for transition probabilities, which includes all phonon processes appearing in the treatment given by van Kranendonk, has been derived. This has been done by Fourier transforming the field gradient instead of the usual power series expansion with regard to the nuclear displacements. The formulae for the point‐ion and the overlap potential models are presented in detail. Fürther, the expressions are used to demonstrate the validity of the power series method for the proceeding potentials. A shell model is suggested in order to include the dynamical changes of the ionic wave functions in the calculation of the field gradient.
Two‐Phonon Processes in Crystals of D Symmetry
Authors: Bercha D. M. , Puga G. D. , Borets A. N. 
Published: July 2007

AbstractIt is established that the absorption in the intermediate infra‐red region in BiOI, BiOBr, and BiOCl has two‐phonon character. Group‐theoretical investigations of the phonon spectrum and two‐phonon infra‐red absorption and Raman scattering for these crystals are Carried out. The selection rules obtained enables one to ascertain what phonon combinations from one or different branches, in what points of the Brillouin zone of crystals of symmetry DJ are allowed or forbidden.
Optical Properties of CrO Ion in Orthorhombic Sulphates
Authors: Radhakrishna S. , Pande K. P. 
Published: July 2007

AbstractVibrational frequencies of CrO ion embedded in orthorhombic sulphates have been determined from optical and infrared absorption studies. In the optical absorption spectra, the electronic levels are found to have a superposed vibration structure, in the regions 2300 to 2750 Á and 3300 to 3850 Á, with alternate strong and weak lines. The set of strong lines is interpreted to be due to the transitions from the ground electronic state to the vibrational levels of the excited state, whereas the set of weaker lines is assigned to the transitions from one of the vibrational levels of the ground electronic state to the vibrational levels of the upper excited electronic state. It is found that the IR forbidden bands become allowed and are observed in these lattices. No splitting is observed in the degenerate modes in IR spectra.
Polariton Fusion in CuCl
Authors: Fröhlich D. , Mohler E. , Uihlein Ch. 
Published: July 2007

AbstractSelection rules and frequency dependence for fusion of two polaritons to a longitudinal exciton or a transverse polariton are discussed for crystals of point symmetry Td. Within certain approximations, the transition probability depends only on the polarization of the two polariton beams and on the K‐vector of the final state. The theoretical predictions are found to be in good agreement with two‐photon absorption measurements for the first exciton in CuCl.
Band Structure and Pseudopotential Form Factors for AlAs
Authors: Hess E. , Topol I. , Schulze K.‐R. , Neumann H. , Unger K. 
Published: July 2007

AbstractA combination of the pseudopotential method with the k p‐method was used to, calculate the complete band structure of AIAs. The pseudopotential form factors were determined by fitting to the known optical transition energies. Effective masaes were calculated for the principally important conduction band minima and the valence band maximum and compared with experimental data so far as possible.
EPR Optical Detection of F Centre Pairs in Alkali Halides. II. Spin‐Lattice Relaxation of the F Centre in Its Relaxed Excited State
Authors: Ruedin Y. , Schnegg P.‐A. , Jaccard C. , Aegerter M. A. 
Published: July 2007

AbstractLike the EPR line of the fundamental state of the F centre in most of the alkali halide crystals, the line attributed to the relaxed excited state detected optically for F centre pairs is also Gaussian in shape. That is explained by an inhomogeneous broadening due to hyperfine interactions with the surrounding nuclei. The measurements of these resonances as a function of the microwave power allow to determine the saturation parameter and the broadening of the elementary line (homogeneous). On the other hand the measurement of the resonance signal as a function of temperature, the other parameters remaining constant, shows that it stays constant for T < 10 °K and decreases for increasing temperature. This is attributed to the spin‐lattice relaxation time T1 of the defect in its relaxed excited state. The relaxation mechanism is characterized by an Orbach process.