Spin-wave relaxation and phenomenological damping in ferromagnetic resonance

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Abstract
Relaxation rates for the uniform precession mode in ferromagnetic resonance, with general elliptical polarization, have been calculated for several microscopic scattering processes using the spin-wave formalism. These results are compared with the widely used phenomenological formulations for ferromagnetic resonance. The results demonstrate in relatively general terms the specific features of the Landau-Lifshitz and Gilbert phenomenological formulations on the one hand, and of what may be called "intrinsic" confluence processes in the microscopic formulation. These formulations are consistent with the assumption of an intrinsic damping parameter describing the motion of the magnetization vector under sufficiently general conditions. The two-magnon process and the Bloch-Bloembergen phenomenological description of damping in ferromagnetic resonance are not consistent with such an assumption.