Ba2NiOsO6: A Dirac-Mott insulator with ferromagnetism near 100 K

TL;DR

Ba2NiOsO6 is a newly synthesized ferromagnetic semiconductor with a charge gap influenced by spin-orbit coupling, exhibiting a unique ferromagnetic insulating state near 100 K, promising for spintronic applications.

Contribution

This work reports the synthesis and characterization of Ba2NiOsO6 as a Dirac-Mott insulator with ferromagnetism near 100 K, highlighting the role of Os6+ spin-orbit coupling in its electronic structure.

Findings

Crystallizes in a double perovskite structure with perfect B-site order.

Exhibits collinear ferromagnetic order above 21 kOe at 5 K.

Spin-orbit coupling of Os6+ is crucial for opening the charge gap.

Abstract

The ferromagnetic semiconductor Ba2NiOsO6 (Tmag ~100 K) was synthesized at 6 GPa and 1500 {\deg}C. It crystallizes into a double perovskite structure [Fm-3m; a = 8.0428(1) {\AA}], where the Ni2+ and Os6+ ions are perfectly ordered at the perovskite B-site. We show that the spin-orbit coupling of Os6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te (Tmag < 180 K), the spin-gapless semiconductor Mn2CoAl (Tmag ~720 K), and the ferromagnetic insulators EuO (Tmag ~70 K) and Bi3Cr3O11 (Tmag ~220 K). It is also qualitatively different from known ferrimagnetic insulator/semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of Ba2NiOsO6 should increase interest in the platinum group oxides, because this new class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.