Intrinsic low-field loss in microwave ferrites

The off-resonance damping parameter due to the three-magnon splitting process is calculated by extending the theory of intrinsic magnetic relaxation processes. The imaginary part of the diagonal component of the microwave permeability tensor is found to decrease with increasing internal magnetic field and to be proportional to the absolute temperature. In magnitude it is somewhat smaller than the subthreshold absorption under parallel pumping, which has a similar physical origin and has previously been calculated and verified by experiments. Since the calculated magnetic damping occurs in all magnetic materials, it is expected to contribute significantly to the insertion loss of many ferrite microwave devices.