Interpretation of low-temperature Mössbauer spectra in the presence of Kondo deviations. II. Population effects inAuYb170

In this paper we first derive the relaxation equations for the populations of the hyperfine levels of the 84-keV state of ${}_{}{}^{170}{}_{}{}^{}\mathrm{Yb}$ in a metal, both in the absence and in the presence of an incipient Kondo effect ($T\gg T_K$). We examine how the corresponding relaxation rate $\frac{1}{T_{1 \mathrm{hf}}}$ is related to the electronic relaxation rate $\frac{1}{T_1}$ extracted from line-profile analysis at higher temperatures. We then indicate how $\frac{1}{T_{1 \mathrm{hf}}}$ can be deduced from the intensity ratio of the two hyperfine lines of low-temperature Mössbauer spectra emitted by a ${}_{}{}^{170}{}_{}{}^{}\mathrm{Yb}$ source. This possibility is to be considered as opening a new "window" for measuring relaxation rates. These theoretical results are applied to the interpretation of the experiments performed with Au ${}_{}{}^{170}{}_{}{}^{}\mathrm{Yb}$ in the 0.3-0.5-K temperature range.