Complex spin waves in metallic ferromagnets

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Abstract
The spin wave modes of a metallic ferromagnet are studied using a short range interaction between the electrons, in the random phase approximation (RPA). Besides confirming known properties of the undamped spin waves found for momentum less than a certain value p1 (such as the existence of negative velocity spin waves) the authors find that the amplitude of the spin waves, relative to the non-spin wave contribution to the transverse spin correlation function, is a monotonic decreasing function of the wavenumber going from unity at p=0 to zero at p=p1. For p>p1, decay of spin waves into Stoner excitations becomes possible and the spin waves are damped. The dynamical transverse susceptibility was studied by analytic continuation. Two branches of complex poles are found for relative magnetization xi <1. (one branch for xi =1).

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