Magnetic resonance of high quality ferromagnetic metal single crystals

Abstract

This paper describes the observations and associated analyses of the microwave resonance absorption of very small, apparently highly perfect, single crystal samples of ferromagnetic metals. The primary focus of this study is on nickel but iron and cobalt are also considered. From the point of view of magnetic resonance, the observed narrow line-widths of these samples suggests that they are of high quality compared to bulk material. The general conclusions drawn are that the limited penetration of the microwave energy into a conducting ferromagnet makes an important contribution to the observed resonance absorption linewidth and shape. A damping term of the Landau-Lifshitz form is also identified and gives, quite accurately, the observed linewidth and shape behaviour both in temperature and frequency; this without an explicit temperature or frequency dependence of the damping ‘constant’. There is no evidence for surface spin pinning being present and, in fact, strong experimental evidence against it playing a role in these studies is presented. The magnetocrystalline anisotropy constants and the g value of nickel metal are deduced from the data. Both $K_1$ and $K_2$ are found to be negative over the entire range studied ($\mathit{130}°$ to $\mathit{635}°K$) and both have rapidly decreasing magnitudes with increasing temperature. The spectroscopic splitting factor, g, is determined to be $\mathit{2.22}\pm \mathit{.03}$ and is independent of temperature and frequency.