Single crystal nickel ferrite films. I. Film preparation,structure and composition

Single crystal Ni ferrite films were prepared by a chemical transport reaction in sandwich arrangement. The technological conditions, the problems of their chemical composition, the structure and the quality of their surface were studied with respect to a further investigation of the magnetic properties of these ferrite films.I would like to thank to Dr. L. ervinka and to M. Janatka for carrying out the X-ray and electron diffraction. My thanks belong also to A. Novák for performing the chemical analysis of the initial nickel ferrite and to the workers in the VUST Laboratory who made some partial measurements.     

Electrical conductivity of inhomogeneous superconductors

The excess electrical conductivity of an inhomogeneous superconducting film is calculated using a Random-Ginzburg-Landau model. Treating the quartic interaction within a self-consistent Hartree-approximation the excess conductivity of a random superconductor is found, for T ? T_c, to be enhanced compared to that of a homogeneous film.     

The transport phenomena of pure and doped p-type ZnSb

The electrical conductivity, the Hall effect and the thermoelectric power in thec andb crystallo-graphic directions as a function of temperature on pure and doped ZnSb single crystals with hole conductivity were studied.The anisotropy of the hole mobility was explained on the basis of the anisotropy of the effective mass of holes in the crystallographic directions and the assumption of isotropic relaxation time. A model of the ZnSb valency band with two equivalent extremes was proposed which made it possible to explain the studied transport phenomena.The authors thank Mrs. V. Míková for preparing the ZnSb single crystals, Mr. J. Kapar for the crystallographic orientation and Mrs. J. Trepeová for her help in the experimental work.     

Modified dispersion relations and sum rules

A systematic treatment of modifications to the usual form of dispersion relations and sum rules is given. The treatment is based on the fact that if a function g(z) has analyticity properties analogous to those of a scattering amplitudef (z), the usual dispersion relation for the productf (z)g(z) holds. After having described the general form of the weight function g(z) we concentrate on cases wheng(z) is large in a pre-chosen region and small elsewhere. Weight functions of this type are useful in practical applications where a weight functiong(z) may enhance a contribution of regions where accurate data are available and suppress those of regions with inaccurate or lacking data.Dedicated to Professor V. Votruba on his sixtieth birthday.     

On the calculation of the bremsstrahlung in the region of the plasma frequency

On the basis of the classical theory of radiation produced in incomplete Coulomb interaction, a formula is derived for the coefficient of the bremsstrahlung of fully ionized plasma. In the region of rectilinear approximation a comparison is made with the results of the quantum formula derived from the Born approximation. Furthermore, the influence of dispersion upon the emission coefficient is taken into account; some relations for the region of dispersion are given.     

Microscopic Calculation of the Dielectric Susceptibility Tensor for Coulomb Fluids II

For a Coulomb system contained in a domain Λ, the dielectric susceptibility tensor χ _Λ is defined as relating the average polarization in the system to a constant applied electric field, in the linear limit. According to the phenomenological laws of macroscopic electrostatics, χ _Λ depends on the specific shape of the domain Λ. In this paper we derive, using the methods of equilibrium statistical mechanics in both canonical and grand-canonical ensembles, the shape dependence of χ _Λ and the corresponding finite-size corrections to the thermodynamic limit, for a class of general ν-dimensional (ν≥2) Coulomb systems, of ellipsoidal shape, being in the conducting state. The microscopic derivation is based on a general principle: the total force acting on a system in thermal equilibrium is zero. The results are checked in the Debye–Hückel limit. The paper is a generalization of a previous one [L. ?amaj, J. Stat. Phys. 100:949 (2000)], dealing with the special case of a one-component plasma in two dimensions. In that case, the validity of the presented formalism has already been verified at the exactly solvable (dimensionless) coupling Γ=2.