We have investigated the crystal structure, magnetic and magnetotransport properties of double perovskites Sr2FeMO6 (M=Mo, W). The materials have been prepared in polycrystalline by solid state reaction. Powder X-ray diffraction analyses revealed that Sr2FeMoO6 (SFMO) and Sr2FeWO6 (SFWO) have the tetragonal cell (space group: 14/mmm) and the orthorhombic cell (space group: 1mmm), respectively. Magnetic measurements indicate that SFMO is a ferromagnet and SFWO is an antiferromagnet with T(subscript N)=35 K at H 5 T. Large magnetoresistance ratio (MR) of~22% (H=3T) at room temperature (RT) was observed in the SFWO compound. However, the SFMO compound did not show any significant MR even at high fields and RT (MR~1%; H=3 T and 300 K). The properties of these two compounds are summarized as follows: SFMO-half-metallic and ferromagnetic; SFWO-insulator and antiferromagnetic. The changes observed by physical measurements are supported by band structure calculations to explain the interaction between the 3d (Fe) 4d (Mo) and 5d (W) orbitals of transition metal ions and oxygen ions.
