Synthesis, crystal and magnetic structure of the new double perovskite Ba2MnMoO6

We describe the preparation and characterization of a new double perovskite of formula Ba2MnMoO6. It has been obtained in polycrystalline form by thermal treatment, in a H-2/N-2 flow, of previously decomposed citrate precursors. This material has been studied by X-ray (XRD) and neutron powder diffraction (NPD): it crystallizes, at room temperature, in the cubic space group Fm3m, and shows an almost perfect ordering between Mn2+ and Mo6+ cations at the B substructure. Below T-N = 10.8 K, it experiences a long range antiferromagnetic ordering that was followed from sequential NPD data. The low-temperature magnetic structure is defined by the propagation vector k = ((1)/(2), (1)/(2), (1)/(2)). The ordered magnetic moment of Mn is found to be 4.04(8) mu(B) at 2 K, suggesting a divalent oxidation state for Mn cations, in a high spin t(2g)(3) e(g)(2) (S = 5/2) electronic configuration.