Crystalline electric field contribution to the magnetoresistance of Pr1−xLaxOs4Sb12

Resistivity measurements were performed on Pr1−xLaxOs4Sb12 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 Pr3+ 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.