The oxygen-deficient Ruddlesden-Popper (RP) phase Sr3Mn 2O6 crystallizes with an ordered array of oxygen vacancies to afford a structure in which the Mn3+ ions exist in a square-pyramidal environment. The MnO5 polyhedra are linked through their corners to form a structure that is related to that observed for the single-layered material, Sr2MnO3.5. The nuclear and magnetic structures of a polycrystalline sample of Sr3Mn 2O6 have been determined using Rietveld analysis of neutron powder diffraction data and electron diffraction techniques. The pure Mn3+ double-layered phase crystallizes in a superstructure of the simple RP subcell: tetragonal, P4/mbm, a=10.8686(2)Å and c=20.2051(3)Å.
Magnetic susceptibility studies suggest a transition at ∼250K to a canted antiferromagnetic ordered structure. The magnetic unit-cell consists of ferromagnetic clusters of corner-sharing MnO5 units, which are antiferromagnetically aligned to other clusters within the layers.