Coherent Potential Approximation for the Impure Heisenberg Ferromagnet

Recent experiments of Svenssonet al.1 have shown that well-defined spin-wave modes exist in disordered antiferromagnets. The localized modes which exist in dilute alloys persist and become dispersive as the concentration is increased. In this paper we present a theory of the disordered Heisenberg ferromagnet which qualitatively reproduces some of the features found experimentally.