Phenomenological damping models as drive to equilibrium

This work gives a new and simple physical perspective on three phenomenological damping models in common use for precession dynamics analyses in ferromagnetic systems: the Landau Lifshitz (LL) model, the Codrington, Olds, and Torrey (COT) model, and the modified Bloch Bloembergen (MBB) model. In the small signal limit, the LL, MBB, and COT models can be derived from three physically different but completely plausible "drive to equilibrium" scenarios. Mathematical forms for the damping rate as a function of the dynamic magnetization m_x(t) are derived for each model. These damping forms have proponents and detractors. The LL and MBB forms have a physical basis in magnon electron scattering and Bloch type spin-spin relaxation processes, respectively. Permalloy films have also been interpreted in terms of a COT model.