ABSTRACT
This chapter explores the nature of the elementary excitations over an amorphous ferromagnetic ground state at a nonzero temperature, or with the application of a small perturbation on the system. In a crystalline ferromagnet any local deviation from the perfect spin alignment does not remain confined in the region, but, owing to exchange coupling, propagates like a wave. The chapter discusses the nature of linear spin waves in amorphous ferromagnets. The spin waves can be thought of as one spin reversal spread coherently over the entire crystal. The chapter explains the situation of spin waves in amorphous ferromagnets with only one magnetic element and other nonmagnetic components. The spectral function has been studied for a variety of amorphous ferromagnets by inelastic scattering of neutrons. One of the surprising facts found in amorphous ferromagnets is that the concept of magnons as non-interacting quasiparticles is valid until a rather high temperature region in contrast to that of crystalline case.
