Landau-Lifshitz Theory of Spin Waves in an Amorphous Ferromagnet

Abstract

A simple semiclassical theory of spin wave propagation in an amorphous Heisenberg ferromagnet is developed. The ferromagnet is assumed to consist of randomly distributed identical magnetic atoms. The discrete spin of the atoms is replaced by a function which varies continuously with position. The theory can be regarded as an extension of the Landau‐Lifshitz and Herring‐Kittel theory of spin waves in crystalline ferromagnets. It is found that both extended and localized spin waves may exist in these systems. The localized spin waves find their origin in the structural randomness. The possible effect that the localized spin waves may have on spin wave resonance is pointed out.