RESUMO
A dynamic spin-fluctuation theory that directly takes into account nonlocality of thermal spin fluctuations and their mode-mode interactions is developed. The Gaussian approximation in the theory is improved by a self-consistent renormalization of the mean field and spin susceptibility due to the third-and fourth-order terms of the free energy, respectively. This eliminates the fictitious first-order phase transition, which is typical for the Gaussian approximation, and yields a proper second-order phase transition. The effect of nonlocal spin correlations is enhanced by taking into account uniform fluctuations in the single-site mean Green function. Explicit computational formulae for basic magnetic characteristics are obtained. The extended theory is applied to the calculation of magnetic properties of Fe-Ni Invar. Almost full agreement with experiment is achieved for the magnetization, Curie temperature, and local and effective magnetic moments.
RESUMO
The pseudopotential model is used for the evaluation of the core level ionisation intensities (by the electron impact). The central atom effective phase shift is calculated for K EELFS spectra in this framework. The Si K EELFS spectra were calculated and compared with the experimental data. The comparison of experimental and calculated results is performed on the base of the electron dispersion law which takes into account electron-plasmon interaction.
