Structural and magnetic properties of double perovskites AA′FeMoO6 (AA′ = Ba2, BaSr, Sr2 and Ca2)

Room temperature x-ray diffraction, magnetization and neutron diffraction measurements up to 500 K have been carried out on polycrystalline bulk double perovskites AA'FeMoO6 (AA' = Ba-2, BaSr, Sr-2, Ca-2) in order to determine and correlate their structural and magnetic properties. As the average ionic radius is diminished, the crystallographic structure evolves from cubic (for AA' = Bat, BaSr) to tetragonal (Sr-2) and finally to monoclinic (Ca-2). In the case of AA' = Sr-2, a novel crossover from a high temperature paramagnetic cubic state to a low temperature ferrimagnetic tetragonal state has been observed. For all the studied compounds, neutron diffraction patterns and magnetization measurements are consistent with a ferrimagnetic ordering of the Fe and Mo sublattices. A remarkable correlation is found between the Curie temperature and the electronic bandwidth, which is controlled by structural parameters.