Magnetostatic Modes in Ferrimagnetic Spheres

Abstract

Ferrimagnetic resonance experiments (9000 Mc/sec, 300°K) have been performed using single-crystal spheres of yttrium iron garnet. Rf magnetic fields of several different configurations were used to excite specific magnetostatic modes. A mounting technique was employed such as to eliminate dielectric inhomogeneities near the sample. Such inhomogeneities arise from the usual quartz or sapphire mounting rods. They have been observed to be responsible for the excitation of more complicated modes than would be expected from the unperturbed cavity fields. It has been found that supposedly spherical specimens produced by the usual tumbling procedures deviate slightly from true sphericity. In these experiments highly polished truly spherical samples were used. With these conditions there is no ambiguity about the identity of the mode representing the spacially uniform precession of the entire spin system. The spacings of the various modes do not vary with the crystal direction along which $H_{\mathrm{dc}}$ is applied. These results contrast with those of White and Solt on manganese ferrite in several respects, viz. the clear identity of the uniform precession and the constant mode spacing for the various crystal directions.