Electron correlation in ferromagnetism. III. dynamical susceptibility in narrow energy bands

Abstract

We present our study of the dynamical susceptibility for a system of electrons in a narrow energy band. The Hamiltonian of the system consists of single-particle energies of electrons in the absence of interactions, the intra-atomic Coulomb interaction, and interatomic Coulomb and exchange interactions. An approximate expression for the susceptibility is derived by using the random-phase approximation. Instability of the paramagnetic state against the ferro- and the antiferromagnetic states is discussed. Also presented is the study of the dynamical susceptibility for a system of electrons with strong intra-atomic interactions where the validity of the random-phase approximation is dubious. In this case, in addition to the conditions for the paramagnetic instability against the ferro- and the antiferromagnetic states, we have also discussed the spin-wave excitations.