Influence of microstructure on relaxation processes and high power properties in polycrystalline YIG

High power material properties, in particular spin-wave dissipation, are often a limiting factor for application design. A theory that can explain the off-resonance losses and the high power behaviour, e.g., the spin-wave linewidth DeltaH(k) determining the onset of the Suhl instabilities, is still missing for polycrystalline ferrites. In the present work the Sparks, Loudon and Kittel (SLK) theory of two-magnon scattering has been extended to explain the influence of the microstructure of the material on its high power microwave properties. Within the same framework we introduce a model which describes the influence of grain size and anisotropy. Good qualitative agreement with previous measurements is achieved without using any fit parameters.