Positive-muon (${\mu }^{+}$) Knight shifts have been measured in the paramagnetic states of ${\mathrm{Pr}}_{1-x}{\mathrm{Nd}}_x{\mathrm{Os}}_4{\mathrm{Sb}}_{12}$ alloys, where $x=0$, 0.25, 0.45, 0.50, 0.55, 0.75, and 1.00. In Pr-substituted ${\mathrm{NdOs}}_4{\mathrm{Sb}}_{12}$ ($x\le 0.75$), but not in ${\mathrm{NdOs}}_4{\mathrm{Sb}}_{12}$, Clogston-Jaccarino plots of ${\mu }^{+}$ Knight shift $K$ versus magnetic susceptibility $\chi$ exhibit an anomalous saturation of $K\left(\chi \right)$ at $\sim -0.5$% for large susceptibilities (low temperatures), indicating a reduction of the coupling strength between ${\mu }^{+}$ spins and $4f$ paramagnetism for temperatures $\lesssim 15$ K. We speculate that itinerant ${\mathrm{Pr}}^{3+}$ quadrupolar excitations, invoked to mediate the superconducting Cooper-pair interaction, might modify the ${\mu }^{+}$-$4f$ ion indirect spin-spin interaction.

• Received 15 May 2014

DOI:https://doi.org/10.1103/PhysRevB.89.235111