Instability of Magnetic Resonance in Single Crystal Spheres of Yttrium Iron Garnet

Abstract

Instabilities in YIG spheres that exist above certain threshold power values of cw microwave field are studied using samples of about $\frac{1}{4}-\frac{1}{2}\hspace{0.17em}\mathrm{mm}$ diam, that have low power line widths of 1 oe or less. Whereas the characteristic behavior such as asymmetrical line shape, “jump” effect etc. is somewhat similar to that reported for disks, the phenomenon is generally different. It has been determined that this instability, which can occur at cw power levels below the threshold for significant spin wave growth, is due entirely to the heating effect of resonance absorption upon the anisotropy energy of the crystal lattice. As a result, the instability is characterized by a threshold curve that follows both the extrema and symmetry of the anisotropy curve for a given orientation. A straightforward theoretical explanation based on familiar relationships is outlined which fits the instability threshold vs orientation curve. The temperature instability provides a technique for measuring the “$g$ ” factor that is believed to be more direct than previous methods.