Spin waves in disordered itinerant-electron ferromagnets

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Abstract
It is shown that there are two distinct contributions to D in disordered itinerant electron systems: the 'average exchange' contribution and the 'magnon scattering' contribution. Only the former has been considered in existing quantitative work on transition metal alloys and only this contribution is retained in deriving a new formula for D within the framework of the KKR-CPA method. Both contributions to D are discussed further using a tight-binding model, and the 'magnon scattering' contribution is related to previous work by Morkowski (1976-77). The success of existing quantitative work on D in transition metal alloys suggests that in most of these systems the 'average exchange' contribution is dominant. However, it is shown for a simple model of an amorphous system that the two contributions are equally important in determining the difference between D in the amorphous and crystalline states.