Muon spin relaxation and nonmagnetic Kondo state in ${\mathrm{PrInAg}}_2$

Muon spin relaxation experiments have been carried out in the Kondo compound ${\mathrm{PrInAg}}_2.$ The zero-field muon relaxation rate is found to be independent of temperature between 0.1 and 10 K, which rules out a magnetic origin (spin freezing or a conventional Kondo effect) for the previously observed specific-heat anomaly at $\sim 0.5\hspace{0.5em}\mathrm{K}.$ At low temperatures the muon relaxation can be quantitatively understood in terms of the muon’s interaction with nuclear magnetism, including hyperfine enhancement of the ${}^{141}\mathrm{Pr}$ nuclear moment at low temperatures. This argues against a ${\mathrm{Pr}}^{3+}$ ground-state electronic magnetic moment, and is strong evidence for the doublet ${\Gamma }_3$ crystalline-electric-field-split ground state required for a nonmagnetic route to heavy-electron behavior. The data imply the existence of an exchange interaction between neighboring ${\mathrm{Pr}}^{3+}$ ions of the order of 0.2 K in temperature units, which should be taken into account in a complete theory of a nonmagnetic Kondo effect in ${\mathrm{PrInAg}}_2.$