Magnetic susceptibility and specific heat of uranium double perovskite oxides Ba2MUO6 (M=Co, Ni)

Double perovskites Ba2MUO6 (M=Co, Ni) were prepared by the solid-state reaction. X-ray diffraction measurements show that both cobalt (nickel) and uranium ions are ordered in the NaCl type over the six-coordinate B sites of the perovskite ABO3. Detailed magnetic susceptibility and specific heat measurements show that Ba2CoUO6 and Ba2NiUO6 order ferromagnetically at 9.1 and 25 K, respectively. From the analysis of the magnetic specific heat, the ground states of the Co2+ and Ni2+ ions were determined.