FMR spectrum of magnetostatic waves in a normally magnetized YIG disk

The absorption of microwaves in a normally magnetized YIG disk has been measured and analyzed. The absorption peaks are interpreted to be caused by magnetostatic waves propagating radially across the disk. The mode numbers of absorption peaks are determined by the aspect ratio of the disk, ${\mathrm{(\omega /\gamma )}}^2{\mathrm{-H}}_i^2$ and B_iH_i −(ω/γ)², where ω is the microwave angular frequency, γ is the gyromagnetic ratio, and H_i and B_i are internal magnetic fields and depend upon the applied magnetic field. The experimental values of the applied magnetic field at which the absorption peaks are caused are in good agreement with the theoretical values. It has been verified both theoretically and experimentally that the new mode absorptions due to the magnetostatic waves exist in the case of ω/γ−[B_i(0)H_i(0)]^1/2 =dH > 0, where B_i(0) and H_i(0) are the internal fields at the disk center. These new mode abosrption peaks tend to shift toward the cutoff point of the usual absorption spectra as the incident microwave power is increased.