Ferromagnetic Resonance in Metal Single Crystals

Microwave susceptibility expressions for ferromagnetic resonance have been derived for metal single crystals possessing crystalline anisotropy. Crystals of uniaxial and cubic magnetic symmetry are considered. When the magnetization M is aligned with the applied field H, the results are equivalent to those of Kittel. When a simple multidomain structure occurs on a crystal face, two resonances are found for a given $H$. These correspond to microwave excitation being perpendicular or parallel to H. These multidomain resonances are related to $H$, saturation magnetization $M$, anisotropy parameter $\frac{K}{M}$, and the ratio of skindepth to domain width. Thus domain spacings can be inferred from microwave measurements. In particular, predictions of the theory are compared with the microwave measurements of Kip and Arnold and magnetic domain pattern observations in the literature. Secondary resonances found in Ni by Reich can also be attributed to a multidomain structure.