A study on the role of some interations in mixed valent systems

Abstract

There are different types of interactions in mixed-valence phenomena. They take place in various rare-earth compounds or intermetallics. Many investigations have been performed to describe the valence transition and different anomalous properties of these mixed-valent compounds, still some phenomena remain unexplained. The ground state and thermodynamical properties depend very much on the approximations considered. This present work describes the role of different new interactions related to mixed-valence phenomena. To perform the study we have considered a four-site extended Falicov-Kimball model. 120 basis vectors are found from a representative state. We have also studied an eight site extended Falicov-Kimball model (EFKM) for one interaction. In this case, 496 basis vectors are constructed. Thermodynamical properties are studied at zero and finite temperatures. The observations show that when any one of the extended interactions like d-f exchange interaction, spin dependent f-d interaction, pair hopping of d electrons, f-d hybridization interaction, Hubbard type interaction etc. is increased, valence transition changes significantly. The roles of hopping of d-electron pairs have been studied also. Every time, specific heat curves exhibit characteristic double-peak structure. The effects of these interactions on entropy and spin susceptibility have also been considered. Previous experimental findings have been compared with observed results as far as possible. All the works show the relevance of the interactions considered in the mixed-valent systems. newline