Spinwave linewidths in polycrystalline YIG

Values of spinwave linewidths derived from measured instability fields for parallel, perpendicular, and oblique pumping butterfly curves in polycrystalline yttrium iron garnet are compared to the theory of Sawado for spinwave scattering by nonmagnetic pores. Reasonable agreement is obtained for a spinwave linewidth of the form ΔHk= A + BΔHk(P), where A and B are parameters which depend on both the pumping angle and the sample microstructure, and ΔHk(p) is the normalized, wavevector dependent pore scattering linewidth of Sawado. A model based on grain boundary scattering is not consistent with the data.