Crystal structures and magnetic properties of 6H-perovskite-type oxides Ba3MIr2O9 (M=Mg, Ca, Sc, Ti, Zn, Sr, Zr, Cd and In)

Crystal structures and magnetic properties of quaternary oxides Ba3MIr2O9 (M=Mg, Ca, Sc, Ti, Zn, Sr, Zr, Cd and In) were investigated. Rietveld analyses of their X-ray diffraction data indicate that they adopt the 6H-perovskite-type structure with space group P63/mmc or, in the case of M=Ca, Sr and Cd, a monoclinically distorted structure with space group C2/c  . The Ir valence configurations are Ba3M2+Ir25+O9 (M  =Mg, Ca, Zn, Sr and Cd), Ba3M3+Ir24.5+O9 (M  =Sc and In) and Ba3M4+Ir24+O9 (M  =Ti and Zr). Magnetic susceptibility and specific heat measurements were carried out. In the Ba3M2+Ir25+O9, the Ir5+ ions have a non-magnetic ground state and the magnetic behavior for these compounds is explained by the Kotani's theory. For Ba3M4+Ir24+O9, the effective magnetic moment of these compounds is significantly small, although the Ir4+ ions have magnetic moment, which indicates the existence of the strong antiferromagnetic interaction between Ir4+ ions in the Ir4+2O9 face-shared bioctahedra. In the case of Ba3M3+Ir24.5+O9, a specific heat anomaly was found at about 10 K (M=Sc) and 1.6 K (M=In), which suggests the magnetic ordering of the magnetic moments of Ir4+ in the (Ir4+Ir5+)O9 bioctahedra.

The schematic crystal structure of Ba3MIr2O9. Among the title compounds, only Ba3M3+Ir24.5+O9 (M=Sc, In) show an antiferromagnetic transition at low temperatures.Figure optionsDownload as PowerPoint slide