bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mössbauer effect study of the hyperfine field at the tin site in PtMnSn
Authors: Rao K. R. P. M. , Iyengar P. K. 
Published: July 2007

AbstractThe magnitude of the hyperfine field at the tin site in the PtMnSn alloy has been measured using the Mössbauer effect technique. The observed field is 7 kOe at 293 °K and 33 kOe at 78 °K. The sign of the field has also been determined and found to be positive. Saturation hyperfine field at the Sn‐site has been estimated using the virtual bound state model of Caroli and Blandin for a range of values of the parameters of the model. It is found that the theory is inadequate since it does not predict even the correct sign of the hyperfine field at the tin site. It is suggested that the hyperfine fields observed at the tin sites in various Heusler (L21) and related Clbstructure alloys could probably be understood on the basis of the model of Campbell in terms of the effective impurity potentials present at the Sn‐sites in the various alloys.
Superconductivity in the palladium‐hydrogen system
Authors: Skośkiewicz T. 
Published: July 2007

AbstractSuperconductivity has been investigated in palladium hydride samples prepared electrolytically. At H/Pd ratios higher than 0.77 a strong dependence of the superconducting critical temperature on H/Pd ratio has been observed. The critical temperature of 6.6 K was found at H/Pd = 0.94. Extrapolation of the experimental data up to H/Pd = 1 gave the critical temperature of stoichiometric PdH about 11 K. It is shown that the normal residual resistivity of a sample can be used for an estimation of the hydrogen content. The measurements of the electrical resistance in the magnetic field revealed a linear dependence of the critical magnetic field on temperature. Extrapolation of Hc down to T = 0 gave an Hc(0) value equal to 1800 Oe independent of H/Pd.
Small polaron model of the electron motion in organic molecular crystals
Authors: Vilfan I. 
Published: July 2007

AbstractThe electron mobility in organic molecular crystals, in particular in anthracene, is calculated applying the small polaron model. The fluctuations of the electron polarization energy are considered as the electron‐phonon interaction. The mobility is calculated in two ways, in the first the electron‐hole correlation is neglected. It is shown that the effect of the electron‐hole correlation is to increase the mobility by about 80%. The calculated and experimental mobility values are compared.
The effect of high magnetic fields on the ground state of hydrogen‐like impurities in semiconductors
Authors: Halbo L. 
Published: July 2007

AbstractA variational calculation has been made of the ground state energy of a semiconductor impurity in the effective mass approximation (EMA), in the presence of high magnetic fields. The field dependence of the computed binding energy and the wave function parameters are presented. The calculation was made for isotropic effective mass as well as for a mass anisotropy corresponding to electrons in germanium. The effect of the many‐valley structure of the conduction band in germanium, and the deviations from the EMA, are discussed.
EPR investigation of paramagnetic centres in β‐rhombohedral boron
Authors: Gewinner G. , Kubler L. , Koulmann J. J. , Jaeglé A. 
Published: July 2007

AbstractA symmetrical EPR line with a g‐factor of 2.0028 is observed in β‐rhombohedral boron at temperatures above 300 °K. The spin density is measured in the range 300 to 1000 °K. It increases exponentially with the temperature and an activation energy of about 0.40 eV is obtained. The line width exhibits a minimum in the neighbourhood of 450 °K. These results suggest a carrier model with localized wave functions. The number of corresponding electronic states is very large. In the neighbourhood of 300 °K, the line width, line shape, and g‐value are within experimental errors the same as those reported for the EPR line observed under illumination with a radiation of about 0.8 μm. The two EPR spectra may thus be attributed to the same electronic states being occupied either by optical or by thermal excitation. Measurements of line width and spin density for the photo‐induced EPR line between 77 and 300 °K are reported and support this hypothesis.
Ferroelectric phase transition in small crystals of BaTiO3
Authors: Bäuerle D. , Genzel L. , Martin T. P. 
Published: July 2007

AbstractInfrared absorption measurements show that the depolarization field in small crystals of BaTiO3 prevents the zero wavevector optical mode from becoming soft. Yet the transition temperature is found to be the same for small crystals and bulk. We suggest that the phase transition in small particles is driven by soft modes with nonzero wavevectors.
Mössbauer studies of thermal neutron radiation damage in an ordered alloy
Authors: Simopoulos A. , Vogl G. 
Published: July 2007

AbstractMössbauer effect measurements on Au197 were done to study neutron radiation damage in the ordered alloy CoPt. Pt196 nuclei were irradiated with neutrons to produce unstable Pt197nuclei which β decay to the Au197 Mössbauer nuclei. The average recoil energy of ≈ 30 eV connected with thermal neutron capture led to replacement collisions of Pt197 ions with their neighbours. The Mössbauer results show that by irradiation at 330 K about 40% of the produced Au197 atoms have left their ordered sites with eight Co and four Pt nearest neighbours and ended up in sites with an average of (5.5 ± 0.3) Co and (6.5 ± 0.3) Pt nearest neighbours. This result can be explained by a model of replacement collisions of the recoil atoms with nearest or next nearest neighbours in the 〈110〉 or 〈100〉 directions. The results are fairly in agreement with computer‐simulation predictions for low‐energy recoil in f.c.c. metals.
Hot‐exciton luminescence in CdSe crystals
Authors: Gross E. , Permogorov S. , Morozenko Ya. , Kharlamov B. 
Published: July 2007

AbstractThe emission spectra of CdSe crystals under the excitation in the region of fundamental absorption with the HeNe laser line λ = 6328 Å have been studied at temperatures 4.2 to 300 °K. A set of narrow emission lines shifted by the energies of an integer number of LO phonons to lower energies from the exciting line has been observed in the region of fundamental absorption. No emission line has been observed at the position shifted by l LO. The intensity of LO‐shifted lines drastically decreases with increasing crystal temperature. It is shown that this temperature dependence and the comparable intensity of multiphonon lines cannot be explained on the basis of a resonant Raman scattering model. The observed line emission was assigned to a luminescence of hot excitons. The latter model can explain both thermal quenching of emission and intensity distribution in the spectrum. In the emission spectra of mechanically polished samples a defect activated 1 LO emission line has been observed. This line is due to the indirect exciton transitions without phonon participation in the partially disordered surface layer. Besides the line structure, the continuous emission background has been observed in the region of fundamental absorption. This background forms the high energy exponential tail of the quasi‐equilibrium exciton emission line n = 1 A and can be considered as Urbach region of the exciton emission spectrum.
Magneto‐seebeck effect and Shubnikov‐de Haas effect in n‐type bismuth telluride
Authors: Schröder B. , von Middendorff A. , Köhler H. , Landwehr G. 
Published: July 2007

AbstractShubnikov‐de Haas experiments were performed between 1.8 and 4.2 K on n‐Bi2Te3 single crystals with carrier concentrations between 1.4 × 1018 and 8.4 × 1019 cm−3.In addition the magneto‐Seebeck effect was measured between 20 and 100 K in transverse magnetic fields up to 6 T (60 kG). The Hall effect and Shubnikov‐de Haas oscillations were observed in fields up to 10.5 T (105 kG). The results of the different physical phenomena may be explained by a two‐conduction‐band model. The best fit of the data is obtained with a value of ΔE = 20 meV for the energy difference between the two band minima and a density of states mass of md2 = O.9 m0 for the upper conduction band. With this set of parameters and the known masses for the lower band both the Shubnikov‐de Haas and magneto‐ Seebeck data can be quantitatively accounted for. Also, previously measured specific heat data can be explained on the same basis.
Influence of vibronic coupling on the dissociation of Frenkel excitons
Authors: Zgierski M. Z. 
Published: July 2007

AbstractThe influence of vibronic coupling on one‐ and two‐particle dissociation processes of Frenkel excitons is investigated. Special attention is paid to the temperature dependence of dissociation processes, in which quanta of intramolecular vibration coupled with excitons take part. Some remarks on activation energy for photoconductivity of anthracene and metal‐free phtalocyanine crystals are given.
Crystal field studies of some rare earth hydroxides
Authors: Kumar V. , Gupta G. K. , Dass N. , Chandra K. 
Published: July 2007

AbstractThe magnetic susceptibility, μeff, and the Schottky specific heat have been calculated over a temperature range 10 to 300 °K in Er(OH)3, Er3+:Y(OH)3, Dy(OH)3, and Ho3+: Y(OH)3 systems. The spectroscopic splitting factors, Curie constants, and extra entropy associated with the Schottky anomaly were compared to experimental results. By reason of the good agreement it was concluded that the crystal electric field parameters used are significantly accurate.
Dipolar contributions to magnetic hyperfine fields in ErxY1−xFe2 and TbxY1−xFe2 compounds
Authors: Dariel M. P. , Atzmony U. , Lebenbaum D. 
Published: July 2007

AbstractMössbauer effect measurements on 57Fe have been carried out in the pseudobinary systems ErxY1−x Fe2 and TbxY1−xFe2 at 4.2, 80, and 300 K. The isotropic part of the hyperfine field acting on the iron nuclei includes a term due to polarization by the localized rare‐earth spin. Magnetic dipolar contributions account only in part for the differences in the magnitude of the hyperfine fields at the inequivalent sites.
Phonon Raman spectra of layer compound GaSe
Authors: Yoshida H. , Nakashima S. , Mitsuishi A. 
Published: July 2007

AbstractRaman scattering spectra of GaSe were examined at various temperatures (80 to 400 K) and the far‐infrared transmittance was obtained in the energy range from 10 to 30 cm−1. It is shown that the band at 20 cm−1 is both Raman‐ and infrared‐active. Results of the resonant Raman enhancement in GaSe indicates that the Raman band at 250 cm−1 is due to a LO mode. Comparison between the Raman spectrum of GaSe and that of Gas confirms this. These facts can be explained by considering the hexagonal GaSe as the ϵ‐type which lacks inversion centre. Six Raman bands observed in GaSe are assigned to normal modes on the basis of the ϵ‐type. An E′ (TO) mode is degenerated accidentally with an E″ mode at 211 cm−1.
Statistical theory of nuclear magnetic relaxation in the rotating frame
Authors: Yulmetev R. M. 
Published: July 2007

AbstractThe statistical theory of the nuclear magnetic relaxation of the spins in a rotating frame has been developed by the theoretical functional method of projecting operators (PO). This method of PO was used for finding the kinetic equation for the spin TCF. A general expression for the relaxation rates in the case of slow and fast thermal motion in the spirit of the well known Kubo‐Tomita theory is determined from the structure of these kinetic equations.
The role of reservoirs of dipole‐dipole interactions in cross‐relaxation
Authors: Skrebnev V. A. 
Published: July 2007

AbstractThe possibility of introducing a reservoir of interactions responsible for cross‐relaxation with the inverse temperature βcr is considered for magnetic samples containing two kinds of spins. It is shown that, despite the nonsecular character of such interaction, the rate of the change of temperature β−1cr can be much smaller than the rate of establishment of equilibrium in the various magnetic sub‐systems of a sample. Solutions of the equations for inverse temperatures of the magnetic sub‐systems are given in the case of a strong coupling with lattice vibrations of one of the Zeeman reservoirs. A comparison with experiment has been carried out.
The linear jahn‐teller effect for an orbital triplet
Authors: Bersuker I. B. , Polinger V. Z. 
Published: July 2007

AbstractThe results of a Jahn‐Teller vibronic problem investigation for an orbital triplet linearly coupled to both a tetragonal e‐ and trigonal tz‐vibration are given, the e‐type vibroni ccoupling constant being taken arbitrary, while the tz one is assumed to be small. All the second order perturbation seria are summarized exactly. The ground and several excited state energies and wave functions as well as the reduction factors are calculated. The latter seems to be very sensible to the variation of the coupling constants.
Magnetic susceptibility of pure boron
Authors: Kubler L. , Gewtnner G. , Koulmann J. J. , Jae ´glé A. 
Published: July 2007

AbstractThe magnetic susceptibility of various β‐rhombohedral boron samples has been measured between 4 and 1300 °K. An unusual paramagnetic component, with an experimental number of centres dependent on the temperature of the form N = 2 N0 exp { ‐ E/kT}, is observed above 500 °K. The obtained experimental values are: ΔE≈ 0.41 eV, N0≈ ss 1.0 X 1022 cm−3. ΔE is assumed to be the consequence of a gap of about 0.82 eV between two narrow bands which do not seem to contribute to the conductivity at least for high temperatures (T > 500 °K). Moreover a second contribution is observed increasing linearly above 300 °K with rising temperature and becoming less diamagnetic. The slope of the second signal versus temperature is 2.8 x 10−11 cm3 g−1 deg−1. A Curie paramagnetic contribution appears below 77 °K, which can be accounted for by a part (5 ppm) of the residual impurities.
Strong coupling between proton and phonon in KDP
Authors: Pak K. N. 
Published: July 2007

AbstractThe correlation function for the proton‐phonon coupled system has been obtained b means of the retarded Green's function. The dynamic susceptibility and the internal energ are evaluated in a random phase approximation. Some discussion has been made on tb results by comparison with those obtained previously by others, in which the emphasis ha been laid on the isotope effects. As a result, it is found that the proton‐phonon couplin is very large and then responsible for the isotope effects as well as the lattice instability.
X‐ray emission study of the electronic structure of aluminium‐gold and aluminium‐copper alloys
Authors: KÄllne E. 
Published: July 2007

AbstractThe Al K emission spectra for aluminium‐gold and aluminium‐copper alloys have been measured and compared with emission spectra obtained from pure metal as well as with photoelectron and Mössbauer spectra. The alloy spectra indicate a charge transfer from aluminium to gold. The alloy Al K band spectra show a low energy peak which is interpreted as transitions from noble metal d‐states admixed with Al 3p‐states to the inner Is core level. The satellite lines Al Kα3α4 also shift besides showing a complex structure in the alloys.
Binding energy of excitonic molecules in isotropic semiconductors
Authors: Huang Wei‐Teh 
Published: July 2007

AbstractThe solution of the Schrödinger equation of the excitonic molecule system has been expanded using Feynman's path integral method, in order to determine the binding energy of the excitonic molecules. For the numerical treatment the Monte‐Carlo method was used. The results show that for the case of comparable mass size of electron and hole the method used is more general and satisfactory than the calculations up to the present time. Good agreement with experimental observations is obtained for the complexes in Cu Br, CuCl, CdS, Cu2O, CdSe, Ge, and Si.
Optical absorption by free polarons in CdO
Authors: Finkenrath H. , Fricke W. , Uhle N. 
Published: July 2007

AbstractThe optical constants of degenerate CdO films were measured at about 10 K in the spectral range around the LO lattice frequency (5 to 24 μm). Besides the free carrier absorption and a tail of the lattice absorption an additional absorption is found above the LO frequency which can be explained by the theory of free polarons. At higher frequencies it is superimposed by further absorption processes with noticeable structure which are unexplained until now.
Optical spectra and electroabsorption of CdP2 and CdP4 single crystals
Authors: Radautsan S. I. , Syrbu N. N. , Teslevan V. E. , Chumak I. V. 
Published: July 2007

AbstractThe anisotropy of the absorption and electroabsorption spectra of CdP2 and CdP4, single crystals has been investigated. A number of interband gaps has been determined and specified. The energies and the type of phonons involved in direct and indirect transitions have been determined. Proceeding from group‐theoretical calculations of the band structure, the transitions in CdP4 have been localised and some regularities of the phonons in CdP2 have been revealed.
The Susceptibility of HoAsO4 near the Magnetic Phase Transition
Authors: Becher W. , Kalbfleisch H. 
Published: July 2007

AbstractUsing a simple but nevertheless sensitive experimental arrangement the ac susceptibility of HoAsO4 was studied near its paramagnetic to antiferromagnetic phase transition at TN = 0.559 K. By these measurements concerning with the temperature and the magnetic field dependence of the susceptibility Fisher's theory connecting the specific heat and the reduced susceptibility of an antiferromagnet could be verified. Both the exchange and dipolar fields are given.
A Note on Percolation Probabilities
Authors: Maschke K. , Overhof H. , Thomas P. 
Published: July 2007

AbstractA bond percolation analysis similar to that recently proposed by Pollak is presented. In contrast to Pollak's work part of the bond correlation is taken into account. This leads to an estimate for the onset of percolation in three‐dimensional random networks. Comparison is made with Monte Carlo and series expansion data for bond percolation on crystalline lattices.
First Excited Librational States for 〈100〉‐, 〈110〉‐, and 〈111〉‐Type Paraelectric Defects in Cubic Crystals
Authors: Dick B. G. 
Published: July 2007

AbstractFirst excited librational eigenstates and energy eigenvalues are deduced in the tunneling approximation and listed for 〈100〉‐, 〈110〉‐, and 〈111〉‐oriented paraelectric defects sites of cubic symmetry. These supplement the existing listings for the librational ground states.
External Multi‐Photon Photoeffect from Impure Semiconductors and Dielectrics
Authors: Freydkin E. S. , Kovarskii V. A. 
Published: July 2007

AbstractThe external multi‐photon photoeffect of impure crystals is analysed by the method of kinetic equations. The role isshown that is played by localized states of the electron mteracting with phonons in forming the energetic distribution of the escaped photoelectrons. An explanation is given of the experiments carried out by Logothetis and Hartman [4]. The recombination effect on the external photocurrent is considered.
Diagram Technique for the Green Function of a Heisenberg Ferromagnet with Arbitrary Spin
Authors: Haberlandt H. , Kühnel A. 
Published: July 2007

AbstractThe diagram technique previously developed by one of the authors for the Green's function of a Heisenberg ferromagnet with spin 1/2 is generalized to arbitrary spin. The summation of diagrams is the main problem in the present paper. The diagrams split into two classes; one of them may be summed with help of Dyson's equation, the other cannot be treated as a contribution to the mass operator. The latter class of diagrams is found to be the series expansion of 〈Sz〉 and 〈S S〉. The resulting spin wave energy corresponds in successive approximations to the results of MFA, of Tyablikov's decoupling, of Dyson, and of the decoupling due to Mubayi and Lange, and Kenan, respectively. The low temperature magnetization is calculated directly from the Green's function and agrees with Callen's result in the highest approximation worked out.
Isoelectronic Broadening of the Yellow Exciton Quadrupole Absorption Line of Cuprous Oxide
Authors: Schwab C. , Goltzene A. , Meyer B. , Nikitine S. 
Published: July 2007

AbstractExperimental results of high resolution absorption measurements of the yellow exciton 1S absorption line of Cu2O single crystals, characterized by chemical and crystallographic analysis are reported. After correction of internal strain effects, a line broadening proportional to the silver content is observed, whereas the oscillator strength remains constant. Finally, these data are discussed in terms of diffusion and radiative recombination life times in order to estimate the possibility of observing the spin‐electron resonance of these excitons.
Change of the Order of a Phase Transition by the Influence of an External Parameter
Authors: Benguigui L. 
Published: July 2007

AbstractIt is investigated how, in a phase transition, the order of the transition may be changed from second to first or vice versa by the influence of a parameter Y. It is supposed that the free energy can be written as the sum of four terms: G1(η) a function only of the order parameter η; G2(X) a function only of X, the conjugate of Y; G3(X, η) a coupling function, and G4 = − YX. Some different examples are examined choosing a simple form for G2(X), and of G3(X, η). Also the case of two external parameters coupled to the order parameter is investigated. The results are discussed in connection with different materials like BaTiO3, PbTiO3, and improper ferroelectrics.
A New Superconducting State
Authors: Fink H. J. 
Published: July 2007

AbstractIn long one‐dimensional superconductors, such as whiskers and thin wires, new current‐carrying states above the critical current were found that are due to spatially periodic solutions of the modulus of the order parameter and spatially periodic super and normal transport currents in parallel. The order parameter is zero a t certain points in the whisker, thereby permitting the phase of the order parameter to slip in time of one singly‐connected superconducting region with respect to the adjacent, the consequence of which is a dc potential difference between the separate singly‐connected superconducting regions. In this model the modulus of the order parameter is time‐independent, the phase is time‐dependent and the difference of the pair electrochemical potentials between adjacent singly‐connected superconducting regions is an integer fraction of the total voltage difference across the whisker. These solutions lead to voltage steps in the dc voltage‐current characteristic of thin whiskers. The upper critical current is derived at which the superconductor becomes completely normal conducting. This current is much larger than the current at which the first voltage step occurs. Agreement with experiments is good.
Resonance Raman Scattering at the Critical Points of Zincblende Crystals
Authors: Jain K. P. , Choudhury Gayatri 
Published: July 2007

AbstractThe results of a calculation of the one‐phonon Stokes‐Raman scattering cross‐section are presented for InAs, GaAs, and InSb using an empirically determined joint density of electron states. These clearly indicate a correlation between the structure in the energy‐dependent Raman cross‐sections and the Van Hove critical points. The broad essential features of light scattering near the M1 edge are brought out by the results. These are large resonance enhancements at the saddle points, deep minima between the resonances and large absolute cross‐sections. The theory is compared with available experimental data.