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 image (M=Mg, Ca, Zn, Sr and Cd), image (M=Sc and In) and image (M=Ti and Zr). Magnetic susceptibility and specific heat measurements were carried out. In the image, the Ir5+ ions have a non-magnetic ground state and the magnetic behavior for these compounds is explained by the Kotaniʹs theory. For image, 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 image, 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.