Crystal and magnetic structure of the complex oxides Sr2MnMoO6, Sr2MnWO6 and Ca2MnWO6:: a neutron diffraction study

A study of the crystallographic and magnetic structure of the double perovskites Sr2MnMoO6, Sr2MnWO6 and Ca2MnWO6 has been carried out on polycrystalline samples using neutron powder diffraction (NPD) data. A room temperature analysis of high-resolution NPD patterns has shown that these compounds crystallize, at room temperature, in the monoclinic space group P2(1)/n. The three perovskites contain divalent Mn cations. Ca2MnWO6 presents the strongest distortion with respect to the ideal cubic perovskite structure. The low-temperature antiferromagnetic ordering has been followed from sequential NPD data. The magnetic structures are defined by the propagation vectors k = (1/2, 0, 1/2) for Sr2MnMoO6 and Sr2MnWO6, and k = (0, 1/2, 1/2) for Ca2MnWO6. The possible arrangements for the Mn2+ magnetic moments have been derived from a group theory analysis.