ABSTRACT
This chapter seeks to formulate a unified effective field theory of amorphous ferromagnets and spin glasses, taking into consideration of the nonuniformity of magnetic moments. The theories basing on the effective field concept are of a relatively simple mathematical character. The effective field theory can be relied on for an approximate description of the major aspects of the phenomena being studied. The simplest and most naive effective field approximation consists in considering only one magnetic atom and replacing its interaction with the remainder of the system by an effective field. The Weiss molecular field approximation replaces all of the exchange interactions in an amorphous magnet by an effective field, so that certain properties of the short-range interaction. The possible magnetic phase diagrams: Weiss approximation, Handrich-Kaneyoshi approximation and Gauss approximation. The chapter discusses some results of the quasiclassical method in amorphous ferromagnets, which is equivalent to the Bethe-Peiels method in a crystalline magnet.
