High-Pressure Synthesis of Double Perovskite BaNiIrO: In Search of a Ferromagnetic Insulator.

Double perovskite oxides with d-d electronic configurations are expected to be ferromagnetic from the Goodenough-Kanamori rules, such as ferromagnetic LaNiMnO. In search of new ferromagnetic insulators, double perovskite BaNiIrO was successfully synthesized by high-pressure and high-temperature methods (8 GPa and 1573 K). BaNiIrO crystallizes in a cubic double perovskite structure (space group: 3̅), with an ordered arrangement of NiO and IrO octahedra. X-ray absorption near-edge spectroscopy confirms the nominal Ni(II) and Ir(VI) valence states. BaNiIrO displays an antiferromagnetic order at 51 K. The positive Weiss temperature, however, indicates that ferromagnetic interactions are dominant. Isothermal magnetization curves at low temperatures support a field-induced spin-flop transition.