Orbital-quenching–induced magnetism in Ba 2 NaOsO 6

The double perovskite Ba 2 NaOsO 6 with heptavalent Os ( d 1 ) is observed to remain in the ideal cubic structure ( i.e. without orbital ordering) despite single occupation of the t 2 g orbitals, even in the ferromagnetically ordered phase below 6.8 K. Analysis based on the ab initio dispersion expressed in terms of an Os t 2 g -based Wannier function picture, spin-orbit coupling, Hund's coupling, and strong Coulomb repulsion shows that the magnetic OsO 6 cluster is near a momentless condition due to spin and orbital compensation. Quenching (hybridization) then drives the emergence of the small moment. This compensation, unprecedented in transition metals, arises in a unified picture that accounts for the observed Mott insulating behavior.