Structural phase transition and the electronic and magnetic properties of Sr2FeMoO6

The nuclear and magnetic structures of Sr2FeMoO6 have been investigated usi ng neutron powder diffraction and Mossbauer spectroscopy at temperatures be tween 10 and 460 K. Fe and Mo atoms are found to order on alternate sites, as expected, giving rise to a double-perovskite-type unit cell. Upon coolin g, a structural phase transition from cubic Fm (3) over barm to tetragonal I4/m occurs at similar to 400 K. In the tetragonal I4/m structure as the te mperature decreases, the FeO6 and MoO6 octahedra-rotate continuously around the c axis by an angle of up to similar to5.6 degrees. In the I4/m phase, the magnetic moments for Fe and Mo order ferrimagnetically. The Fe magnetic spins first align along the c direction and then rotate to an angle of sim ilar to 54 degrees with respect to the c axis; the refined Fe magnetic mome nt saturates at similar to4.3 mu (B). Mossbauer spectroscopy measurements s how that the average valence of Fe is intermediate between the high spin co nfiguration values of Fe+2 and Fe+3. The temperature dependence of the mean hyperfine field is in good agreement with the neutron-diffraction results and gives the same transition temperature.