High-Field Nuclear Relaxation ofYb173in DiluteAuYbAlloys: Evidence for Anisotropic Conduction-Electron Exchange

Relaxation rates of the ${}_{}{}^{173}{}_{}{}^{}\mathrm{Yb}$ nuclear resonance in $\mathrm{Au}\mathrm{Yb}$ have been measured in the low-temperature local-moment regime (${\omega }_{e}T_2^{}{}_{}{}^e\gg 1$). The measured rates can be accounted for by virtual transitions of the ${\mathrm{Yb}}^{3+}$ moment within the ${\Gamma }_7$ doublet caused by exchange interactions with host conduction electrons. The absence of significant contributions to the high-field ${}_{}{}^{173}{}_{}{}^{}\mathrm{Yb}$ relaxation rates from virtual transitions to the ${\Gamma }_8$ quartet requires an anisotropic form for the exchange.