First-principles study on electronic properties of the pyrochlore oxide Cd2Os2O7

The pyrochlore oxide Cd2Os2O7 is one of 5d pyrochlore oxides in which the interplay of geometrical frustration, electron correlation, and spin-orbit coupling is expected. This compound exhibits a metal-insulator transition at 227 K, below which the emergence of a magnetic order has been suggested by experiments. Despite extensive studies for over thirty years, however, the nature of the low-temperature phase remains to be clarified. We depict the ground-state phase diagram based on the LSDA+$U$ method (LSDA denotes local spin density approximation). We find that the all-in/all-out non-collinear magnetic order is stable in a wide range of $U$. We show that the easy-axis anisotropy arising from the spin-orbit coupling plays a significant role in stabilizing the all-in/all-out magnetic order. A pseudo gap extending up to high energy is found to appear near a continuous metal-insulator transition between an antiferromagnetic metallic phase and an antiferromagnetic insulating phase. Based on the computed results, we discuss possible origins of peculiar low-temperature properties observed in experiments.