Separation of anisotropy and porosity contributions to inhomogeneous broadened FMR linewidth in polycrystalline YIG

The FMR linewidth of the 210-, 110-and 220-magnetostatic modes in a highly polished and annealed polycrystalline YIG sphere have been measured as a function of frequency at different temperatures. From these results a separation into anisotropy and porosity induced line broadening contributions was accomplished. The results show that both line broadening contributions arise mainly from scattering to low and medium k states of the spinwave manifold. Excellent quantitative agreement was found with Schlömann's anisotropy broadening theory over the whole range of the spinwave manifold covered by the investigated modes. The obtained porosity broadening contribution contradicts the theoretical predictions using the density of spinwave states as a scattering reservoir. A qualitative explanation of this result can be given by taking into account the dispersion of the spinwave angle Θ0.