Possible antiferroquadrupolar order in the Kondo semiconductor CeOs4Sb12

We report the results of dc magnetization, thermal expansion, and magnetostriction measurements of the Kondo semiconductor CeOs4Sb12. These results provide a magnetic-field-temperature phase diagram for the three principal axes of the cubic crystal [100], [110], and [111] and reveal the magnetic anisotropy of the three ordered phases A, B, and C. The magnetic anisotropy of the transition temperature TC from the paramagnetic phase to the C phase is T [111] C > TC[110] > T[100] C . At low temperatures, the magnetization has a distinct magnetic anisotropy in high magnetic fields: M[100] > M[110] > M[111]. This ratio of magnetization is in good agreement with that of the magnetically anisotropic xe002;67 quartet. The observation indicates that the crystalline electric field ground state is a xe002;67 quartet and that the c-f hybridization effect is nearly isotropic. In addition, comparison of the present experimental results with numerical calculations of a two-sublattice model using the mean-field approximation suggests that the C phase is a xe002;5-type antiferroquadrupolar ordered state despite the presence of strong c-f hybridization effects. In this case, the increase in TC due to the external field is mainly caused by the xe002;2-type antiferro-octupolar interaction.

Automated summary

The results of magnetization, thermal expansion, and magnetostriction measurements of CeOs4Sb12 reveal magnetic anisotropy and phase differences in the ordered phases A, B, and C. The magnetization at low temperatures in high magnetic fields shows significant anisotropy, with the ratio M[100] > M[110] > M[111] consistent with the xe002;67 quartet. The comparison between experimental results and numerical calculations suggests that the C phase is an antiferroquadrupolar ordered state, mainly influenced by antiferro-octupolar interaction.