Structural phase transition and magnetic properties of double perovskites Ba2CaMO6 (M=W, Re, Os)

Structures and magnetic properties for double perovskites Ba2CaMO6 (M=W, Re, Os) were investigated. Both Ba2CaReO6 and Ba2CaWO6 show structural phase transitions at low temperatures. For Ba2CaReO6, the second order transition from cubic image to tetragonal I4/m has been observed near 120 K. For Ba2CaWO6, the space group of the crystal structure is I4/m at 295 K and the transition to monoclinic I2/m has been observed between 220 K. Magnetic susceptibility measurements show that Ba2CaReO6 (image) and Ba2CaOsO6 (image) transform to an antiferromagnetic state below 15.4 and 51 K, respectively. Anomalies corresponding to their structural phase transition and magnetic transition have been also observed through specific heat measurements.