MHz conductivity, torque magnetometer, and magnetization measurements are reported on single crystals of ${\mathrm{CeOs}}_4{\mathrm{Sb}}_{12}$ and ${\mathrm{NdOs}}_4{\mathrm{Sb}}_{12}$ using temperatures down to 0.5 K and magnetic fields of up to 60 tesla. The field-orientation dependence of the de Haas-van Alphen and Shubnikov-de Haas oscillations is deduced by rotating the samples about the $\left[010\right]$ and $\left[0\overline{1}1\right]$ directions. The results indicate that ${\mathrm{NdOs}}_4{\mathrm{Sb}}_{12}$ has a similar Fermi surface topology to that of the unusual superconductor ${\mathrm{PrOs}}_4{\mathrm{Sb}}_{12}$, but with significantly smaller effective masses, supporting the importance of local phonon modes in contributing to the low-temperature heat capacity of ${\mathrm{NdOs}}_4{\mathrm{Sb}}_{12}$. By contrast, ${\mathrm{CeOs}}_4{\mathrm{Sb}}_{12}$ undergoes a field-induced transition from an unusual semimetal into a high-field, high-temperature state characterized by a single, almost spherical Fermi-surface section. The behavior of the phase boundary and comparisons with models of the band structure lead us to propose that the field-induced phase transition in ${\mathrm{CeOs}}_4{\mathrm{Sb}}_{12}$ is similar in origin to the well-known $\alpha \text{−}\gamma$ transition in Ce and its alloys.

• Received 18 August 2016
• Revised 25 October 2016

DOI:https://doi.org/10.1103/PhysRevB.94.205140