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 P 2₁ /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.