Relaxation mechanism for ordered magnetic materials

We have formulated a relaxation mechanism for ferrites and ferromagnets (insulators and metals) whereby the coupling between the magnetic motion and lattice is based purely on continuum arguments concerning magnetostriction. This theoretical approach contrasts with previous mechanisms based on microscopic formulations of spin-phonon interactions employing a discrete lattice. Our model explains the scaling of the intrinsic ferromagnetic resonance linewidth with frequency, with temperature {proportional to 1/M-s(T)} and the anisotropic nature of magnetic relaxation in ordered magnetic materials. Here, M-s(T) is the thermal saturation magnetization. Without introducing adjustable parameters, our model is in reasonable quantitative agreement with experimental measurements of the intrinsic magnetic resonance linewidths of important class of ordered magnetic materials including both insulators and metals.