Absorption Spectra by Magnetostatic Spin Waves in Axially Magnetized YIG Rods

The absorptions of microwave in axially magnetized YIG rods were measured and analyzed. The absorption peaks are interpreted to be caused by magnetostatic spin waves propagating along the rod axis. The mode numbers of absorption peaks are determined by the sample shape and the value of ωs/γ-Hi(0), where ωs is the microwave angular frequency, γ is the gyromagnetic ratio, and Hi(0) is the internal magnetic field at the rod center and depends upon the applied magnetic field. In calculations of mode number and mode separation, the demagnetizing field Hd in the rod is approximated by a quadratic equation of the square of normalized position ζ. The mode separations are independent of the microwave frequency. The experimental values of the applied magnetic field at which the absorption peaks are caused coincide with the theoretical values.