The origin of magnetism in a supposedly nonmagnetic osmium oxide.

Moretti Sala M., Agrestini S., Borgatti F., Boscherini F., da Cruz Pinha Barbosa V., Faure Q., Florio P., Franchini C., Frassineti J., Ghiringhelli G., Mitrovic V., Sahle C.J., Sanna S., Tran M.P., Woodward P.
  Martedì 13/09   09:00 - 13:30   Aula D - Marianna Ciccone   II - Fisica della materia   Presentazione
Despite the fact that a system characterized by a $5d^{1}$ spin-orbit-coupled electronic configuration should be nonmagnetic and metallic, $Ba_{2}NaOsO_{6}$ is a Mott insulator and develops a canted antiferromagnetic long-range order. $Ab initio$ quantum chemical calculations show that, even for perfectly cubic environment, the strong Os $5d$-O $2p$ hybridization (covalency) generates a finite magnetic moment; but mostly, Jahn-Teller effects reduce the local site symmetry and enhances the magnetic moment. Here we probe $Ba_{2}Na_{1-{x}}Ca_{x}OsO_{6}$ by means of resonant inelastic X-ray scattering (RIXS) at the Os $L_{3}$ edge in order to access its electronic structure directly and monitor $d$ - $d$ and charge-transfer excitations as fingerprints of the effective ligand field symmetry and strength. We extract quantitative information on spin-orbit coupling, crystal field (including the degree of Jahn-Teller distortions), and covalency characterizing $Ba_{2}NaOsO_{6}$ and its Ca doped variants, and provide insights into the origin of their unexpected transport and magnetic properties.