Zero- and longitudinal-field muon spin relaxation experiments have been carried out in the alloy series $\mathrm{Pr}{\left({\mathrm{Os}}_{1-x}{\mathrm{Ru}}_x\right)}_4{\mathrm{Sb}}_{12}$ and ${\mathrm{Pr}}_{1-y}{\mathrm{La}}_y{\mathrm{Os}}_4{\mathrm{Sb}}_{12}$ to elucidate the anomalous dynamic muon spin relaxation observed in these materials. The damping rate $\Lambda$ associated with this relaxation varies with temperature, applied magnetic field, and dopant concentrations $x$ and $y$ in a manner consistent with the “hyperfine enhancement” of ${}^{141}\mathrm{Pr}$ nuclear spins first discussed by Bleaney [Physica (Utrecht) 69, 317 (1973)]. This mechanism arises from Van Vleck-like admixture of magnetic ${\mathrm{Pr}}^{3+}$ crystalline-electric-field-split excited states into the nonmagnetic singlet ground state by the nuclear hyperfine coupling, thereby increasing the strengths of spin-spin interactions between ${}^{141}\mathrm{Pr}$ and muon spins and within the ${}^{141}\mathrm{Pr}$ spin system. We find qualitative agreement with this scenario and conclude that electronic spin fluctuations are not directly involved in the dynamic muon spin relaxation.

• Received 16 April 2007

DOI:https://doi.org/10.1103/PhysRevB.76.014527