Spin-orbit coupling, strong correlation, and insulator-metal transitions: the J$_{ m eff}$ =3\2 ferromagnetic Mott insulator Ba$_{2}$NaOsO$_{6}$

摘要

The double perovskite Ba$_{2}$NaOsO$_{6}$ (BNOO), an exotic example of a veryhigh oxidation state (heptavalent) osmium $d^1$ compound and also uncommon bybeing a ferromagnetic Mott insulator without Jahn-Teller (JT) distortion, ismodeled using the density functional theory (DFT) hybrid functional based exactexchange for correlated electrons (oeeHyb) method and including spin-orbitcoupling (SOC). The experimentally observed narrow gap ferromagnetic insulatingground state is obtained, with easy axis along [110] in accord with experiment,providing support that this approach provides a realistic method for studyingthis system. The predicted spin density for [110] spin orientation is nearlycubic (unlike for other directions), providing an explanation for the absenceof JT distortion. An orbital moment of -0.4$\mu_B$ strongly compensates the+0.5$\mu_B$ spin moment on Os, leaving a strongly compensated moment more inline with experiment. Remarkably, the net moment lies primarily on the oxygenions. An insulator-metal transition by rotating the magnetization directionwith an external field under moderate pressure is predicted as one consequenceof strong SOC, and metallization under moderate pressure is predicted.Comparison is made with the isostructural, isovalent insulator Ba$_2$LiOsO$_6$which however orders antiferromagnetically.