Derivation of Transverse Spin-Wave Dynamics from a Kinetic Equation in a Rotating Reference Frame

Abstract

In 1997 Fomin challenged the results of several theoretical groups who had predicted that there could be finite damping of spin-waves in the limit T → 0. His method involved deriving a Lagrangian in a reference frame tied to the oscillating magnetization. He claimed to show that there was no diffusive damping (that is, of second order in wave vector q). We reopen this question by examining, under similar conditions, how a kinetic equation behaves in an equivalent reference frame. We arrive at Fomin’s equations modified by inclusion of q2 damping of the spin-wave modes. Our result sharpens and perhaps clarifies the question of the so-called “zero-temperature relaxation.”