The double perovskite \bnoo with heptavalent Os (d1) is observed to remain in the ideal cubic structure ({\it i.e.} without orbital ordering) despite single occupation of the t2g orbitals, even in the ferromagnetically ordered phase below 6.8 K. Analysis based on the {\it ab initio} dispersion expressed in terms of an Os t2g-based Wannier function picture, spin-orbit coupling, Hund's coupling, and strong Coulomb repulsion shows that the magnetic OsO6 cluster is near a moment-less 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.
@article{arxiv.0709.2520,
title = {Orbital-quenching-induced magnetism in Ba_2NaOsO_6},
author = {K. -W. Lee and W. E. Pickett},
journal= {arXiv preprint arXiv:0709.2520},
year = {2007}
}