Resolved "Fine Structure" in the Magnetic Resonance of a Localized Moment in a Metal

Abstract
The first observation of the resolved fine-structure splitting of a localized moment in a metal is reported in the EPR spectrum of single-crystal dilute Au:Gd alloys. A theory of line narrowing of fine-structure lines from spin-spin couplings and localized-conduction electron exchange is developed. The narrowing distorts the observed resonance line shape, and is essential to the extraction of the fine-structure splitting parameter: b4=20±1 G.