Crystal-field and spin-exchange parameters inAg−DyandAg−Er

We report our measurements of the temperature dependence of the static susceptibility and electron spin resonances for the systems $\mathrm{Ag}-{}_{}{}^{164}{}_{}{}^{}\mathrm{Dy}$ and $\mathrm{Ag}-\mathrm{E}\mathrm{r}$. For both systems we determine the ground state is ${\Gamma }_7$ separated from a ${\Gamma }_8$ excited state by $\Delta =11.5\mathrm{}\pm 1$ K, and 30 ± 5 K, respectively. The overall multiplet splitting is 160 ± 25 K for both. In addition to unambiguously identifying the crystal-field parameters, the reflection and transmission electron-spin-resonance spectra are analyzed in terms of a $J(k,k^{\prime })\overrightarrow{\mathrm{S}}·\overrightarrow{\mathrm{s}}$ model. We find that the ratio of the appropriate averages of $J(k,k^{\prime })$ as determined from the temperature dependence of the $g$- shift and linewidth data, $\frac{J_g}{J_{\Delta H}}$, to be $\simeq 2$ (for a free-electron density of states).