A review of microwave relaxation in polycrystalline ferrites

The microwave losses in polycrystalline ferrites can be separated into two parts: those associated with resonance (inhomogeneous linebroadening and two magnon processes) and intrinsic losses. In recent years, both types have been studied in great detail. The near-resonance relaxation can be quantitatively explained by anisotropy and/or porosity scattering if the secondary scattering among spin-waves and spin-wave relaxation are taken into account. The off-resonance relaxation is found to be quite sensitive to the polycrystal microstructure. Several mechanisms, including transit time limited relaxation and magnetostrictive phonon scattering, appear to be important, but the understanding of the basic loss processes is far from complete.