Saturation Effects in Ferrimagnetic Resonance

Saturation curves of susceptibility as a function of rf magnetic field have been measured for a number of samples of polycrystalline yttrium iron garnet of varying linewidth. The curves exhibit a region of susceptibility linear in ${\text{1/h}}_{\mathrm{rf}}$ at high $\mathrm{rf}$ powers. The region of the initial decline in susceptibility is linear in $h_{{\mathrm{rf}}^2}$ , which is predicted both by a small signal relation derived from Callen's ferromagnetic dynamical equation and by a calculation of Schlömann which includes inhomogeneity interactions. A new method of determining the critical field for spinwave build-up is discussed. This method takes account of the fact that the initial decline in susceptibility is not simply due to the Suhl mechanism for saturation in ferrites.