Orbital-quenching-induced magnetism in Ba_2NaOsO_6

TL;DR

This paper explains how orbital quenching and hybridization in Ba_2NaOsO_6 lead to a small magnetic moment despite a single electron in the t_{2g} orbitals, revealing a unique spin-orbital compensation mechanism.

Contribution

It introduces a new understanding of orbital quenching and hybridization effects causing magnetism in Ba_2NaOsO_6, combining ab initio analysis with spin-orbit and Coulomb interactions.

Findings

The OsO_6 cluster is near a moment-less state due to spin and orbital compensation.

Orbital hybridization drives the emergence of a small magnetic moment.

The model explains the observed Mott insulating behavior.

Abstract

The double perovskite \bnoo with heptavalent Os ($d^1$) is observed to remain in the ideal cubic structure ({\it i.e.} without orbital ordering) despite single occupation of the $t_{2g}$ 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 $t_{2g}$-based Wannier function picture, spin-orbit coupling, Hund's coupling, and strong Coulomb repulsion shows that the magnetic OsO$_6$ 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.