Relaxation of Local-Moment Nuclei in Metals

Relaxation processes for the nuclei of dilute $S$-like local moments in metals are investigated using both perturbation and dynamic-susceptibility techniques. In contrast to host nuclear relaxation, terms analogous to the Benoit-de Gennes-Silhouette (BGS) and Giovannin-Heeger (GH) processes are obtained in the local case by working only to second order in $J_{\mathrm{sd}}$. The two methods of calculation are found, using the dynamic susceptibilities of Götze and Wölfle, to agree exactly within the approximations used. Contrary to the traditional view, the BGS process is found to consist of both real and virtual local-moment-excitation terms, becoming a purely virtual mechanism for large $\frac{H_0}{T}$. The GH process appears as an interference effect between the first-order (Korringa) term and the virtual BGS term. A similar relationship is believed to hold in the host-relaxation case. The local $T_2$ is found to behave rather differently from $T_1$ at low temperatures, with $T_1$ and $T_2$ merging into a single isotropic field-independent rate for sufficiently small $\frac{H_0}{T}$. The present calculations provide a qualitative understanding of the $\mathrm{Ag}\mathrm{Mn}:{}_{}{}^{55}{}_{}{}^{}\mathrm{Mn}$ saturation results given by Okuda and Date.