Room temperature x-ray diffraction, magnetization and neutron diffraction measurements up to 500 K have been carried out on polycrystalline bulk double perovskites AA'FeMoO 6 (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' = Ba 2 , 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.
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Ritter et al. (2000) studied this question.
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