High-Pressure Synthesis of 5d Cubic Perovskite BaOsO₃ at 17 GPa: Ferromagnetic Evolution over 3d to 5d Series

In continuation of the series of perovskite oxides that includes 3d⁴ cubic BaFeO₃ and 4d⁴ cubic BaRuO₃, 5d⁴ cubic BaOsO₃ was synthesized by a solid-state reaction at a pressure of 17 GPa, and its crystal structure was investigated by synchrotron powder X-ray diffraction measurements. In addition, its magnetic susceptibility, electrical resistivity, and specific heat were measured over temperatures ranging from 2 to 400 K. The results establish a series of d⁴ cubic perovskite oxides, which can help in the mapping of the itinerant ferromagnetism that is free from any complication from local lattice distortions for transitions from the 3d orbital to the 5d orbital. Such a perovskite series has never been synthesized at any d configuration to date. Although cubic BaOsO₃ did not exhibit long-range ferromagnetic order unlike cubic BaFeO₃ and BaRuO₃, enhanced feature of paramagnetism was detected with weak temperature dependence. Orthorhombic CaOsO₃ and SrOsO₃ show similar magnetic behaviors. CaOsO₃ is not as conducting as SrOsO₃ and BaOsO₃, presumably due to impact of tilting of octahedra on the width of the t_2g band. These results elucidate the evolution of the magnetism of perovskite oxides not only in the 5d system but also in group 8 of the periodic table.