Muon spin rotation and relaxation in Pr1–xNdxOs4Sb12: Paramagnetic states.

Positive-muon (μ+) Knight shifts have been measured in the paramagnetic states of Pr1−xNdxOs4Sb12 alloys, where x=0, 0.25, 0.45, 0.50, 0.55, 0.75, and 1.00. In Pr-substituted NdOs4Sb12 (x≤0.75), but not in NdOs4Sb12, Clogston-Jaccarino plots of μ+ Knight shift K versus magnetic susceptibility χ exhibit an anomalous saturation of K(χ) at ∼−0.5% for large susceptibilities (low temperatures), indicating a reduction of the coupling strength between μ+ spins and 4f paramagnetism for temperatures ≲15 K. We speculate that itinerant Pr3+ quadrupolar excitations, invoked to mediate the superconducting Cooper-pair interaction, might modify the μ+-4f ion indirect spin-spin interaction. [ABSTRACT FROM AUTHOR]