Magnetoresistance of Pr$_{1-x}$La$_x$Os$_4$Sb$_{12}$: Disentangling local crystalline-electric-field physics and lattice effects

TL;DR

This study investigates the magnetoresistance of Pr$_{1-x}$La$_x$Os$_4$Sb$_{12}$ single crystals at very low temperatures and high magnetic fields, revealing the roles of crystalline-electric-field physics and lattice effects in the material's behavior.

Contribution

It disentangles local CEF effects from lattice interactions in the magnetoresistance of Pr$_{1-x}$La$_x$Os$_4$Sb$_{12}$, highlighting the limitations of the CEF model.

Findings

Residual resistivity shows a smeared step around 9 T.

Weak field-direction dependence suggests interactions beyond the CEF model.

Dome-shaped magnetoresistance in certain compositions likely due to antiferroquadrupolar fluctuations.

Abstract

Resistivity measurements were performed on Pr$_{1-x}$La$_x$Os$_4$Sb$_{12}$ single crystals at temperatures down to 20 mK and in fields up to 18 T. The results for dilute-Pr samples ($x=0.3$ and 0.67) are consistent with model calculations performed assuming a singlet crystalline-electric-field (CEF) ground state. The residual resistivity of these crystals features a smeared step centered around 9 T, the predicted crossing field for the lowest CEF levels. The CEF contribution to the magnetoresistance has a weaker-than-calculated dependence on the field direction, suggesting that interactions omitted from the CEF model lead to avoided crossing in the effective levels of the Pr$^{3+}$ ion. The dome-shaped magnetoresistance observed for $x = 0$ and 0.05 cannot be reproduced by the CEF model, and likely results from fluctuations in the field-induced antiferroquadrupolar phase.