Muon location and muon dynamics in ${\mathrm{DyNi}}_5$

In ${\mathrm{DyNi}}_5,$ the muon localizes at the $6i$ (1/2,0,0.1) interstitial site and below $\sim 80\mathrm{K}$ a second muon site becomes populated, the metastable $6_{\mathrm{ring}}$ site. We determine the mean residence time of the muon in this ring site and analyze its temperature dependence with a multiphonon quantum diffusion process. The coincidence energy is measured to be $E_a{/k}_B=400\mathrm{}$ (20) K and the tunneling matrix element $J=0.21\mathrm{}$ (7) meV. A comparison with ${\mathrm{GdNi}}_5$ gives insight in the muon potential well scheme in these compounds. We attribute the large diversity of muon sites in $R{\mathrm{Ni}}_5$ series, where R is a rare earth element, to the relatively low density of states at the Fermi level.