Extended Theory of Magnon Sideband Shapes. I. Impure Three-dimensional Ferromagnets

Abstract

A calculation of magnon sideband lineshapes is given which uses a simple phenomenological Hamiltonian allowing of an exact solution. The perturbation Hamiltonian has an improved form compared' with that used by Richardson (1974). We consider the effect of a small concentration of substitutional spin impurities on the sideband. An example of an f.c.c. ferromagnetic crystal is studied in detail, and the conditions for the appearance of local modes due to the impurity are discussed. The possibility of resonance modes occurring within the absmption band is considered but, for the f.c.c. crystal studied here, this appears to be unlikely to within the accuracy of the numerical calculations undertaken.