Introduction to an Analysis of Ferromagnets with Dipole–Dipole Interactions

Abstract

The harmonic spectrum of a ferromagnet with dipole–dipole interactions is investigated. It is shown that the dipole–dipole interaction can be treated as a perturbation only after preparing of the Hamiltonian of the system. This preparation consists in elimination of linear terms of the Hamiltonian and in evaluation of the correct harmonic spectrum with respect to the fact that the system does not conserve the total number of quasi‐particles. The approach suggested is valid only in the presence of strong external electromagnetic fields. Copyright © 1974 WILEY‐VCH Verlag GmbH & Co. KGaA