Muon spin rotation and relaxation in Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$: Paramagnetic states

TL;DR

This study investigates the magnetic properties of Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ alloys using muon spin rotation and relaxation, revealing anomalous saturation in Knight shifts linked to Pr substitution and potential effects of quadrupolar excitations.

Contribution

It provides new insights into the magnetic interactions in Pr-Nd alloy systems and suggests a link between quadrupolar excitations and muon-spin coupling modifications.

Findings

Anomalous saturation of Knight shift at low temperatures in Pr-substituted alloys.

Reduction of muon-$4f$ ion coupling strength below 15 K.

Possible influence of quadrupolar excitations on magnetic interactions.

Abstract

Positive-muon ($\mu^+$) Knight shifts have been measured in the paramagnetic states of Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ alloys, where $x =$ 0, 0.25, 0.45, 0.50, 0.55, 0.75, and 1.00. In Pr-substituted NdOs$_4$Sb$_{12}$ ($x \le$ 0.75), but not in NdOs$_4$Sb$_{12}$, Clogston-Jaccarino plots of $\mu^+$ Knight shift~$K$ versus magnetic susceptibility~$\chi$ exhibit an anomalous saturation of $K(\chi)$ 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 Pr$^{3+}$ quadrupolar excitations, invoked to mediate the superconducting Cooper-pair interaction, might modify the $\mu^+$-$4f$ ion indirect spin-spin interaction.