Ferromagnetism at Very High Frequencies II. Method of Measurement and Processes of Magnetization

A method for measuring the complex permeability, $\mu$, of a ferromagnetic metal is described. The determination of both components of $\mu$ is accomplished by a simultaneous measurement of the changes in attenuation and phase velocity introduced into a conducting system by the ferro-magnetism of one of its walls. An experimental technique involving pulsed magnetic fields is used. Values of $\mu$ for samples of magnetic iron at 200 and 975 Mc as a function of a polarizing magnetic field (which is parallel to the high frequency field) are compared to the static incremental permeabilities measured on the same sample. The interpretation of the experimental results indicates several characteristics of the magnetization in iron: the upper limit of domain dimensions in polarizing fields less than 500 oersteds is ${10}^{-4\mathrm{}}$ cm; domains have different degrees of stability in the applied field; "weak-field domain" wall displacements are practically eliminated at the frequencies used; spin rotation and "strong-field domain" wall displacements are only slightly damped and contribute to the magnetization in weak as well as strong fields. Studies of hysteresis phenomena are discussed, and results on two types of permalloy presented.