A Green function theory of spin waves in randomly disordered magnetic systems. I. The ferromagnet

Abstract

The authors present a new technique for discussing the behaviour of spin waves in a ferromagnetically ordered system where the spins occupy random positions on a lattice. It is shown how a Hamiltonian and Green function appropriate to this random ferromagnet may be set up and used to describe the dynamics of such a system. An approximate evaluation of the averaged Green function gives the renormalization and damping of a spin wave mode due to disorder. An estimate of the critical concentration of the spin system is then given, and the authors conclude with a discussion of the effects of disorder on the spectral density function and density of states.