Effect of Excitonic Correlations on Magnetic Order in Mixed Valence 4f-Systems

Abstract

An attractive interaction between conduction electrons and 4f-holes has been incorporated into the periodic Anderson model (PAM). This model Hamiltonian has been approximated by the full mean-field decoupling of the electron-hole interaction and also the 4f Coulomb repulsion. The approximated Hamiltonian is in fact a renormalized PAM where the coupling constants themselves contain terms like average f−, d−, level occupations n¹ and n^d respectively and the excitonic correlation <d⁺ _iσf_iσ> = γ_σ which have to be determined self-consistently. The Curie temperature T_c has been studied as a function of the 4f-level position E_f for a fixed Bloch band width W for different values of the particle-hole attractive strength U_fd. The presence or absence of excitonic correlations does not seem to affect the qualitative behaviour of T_c as a function of E_f. However, the presence of U_fd, and γ_σ-destabi1ize the long range magnetic order which is reflected as a fall in T_c.