Structural-Magnetic Properties Relationship in a New Commensurate Material: Sr9Mn5Co2O21

Polycrystalline Sr9Mn5Co2O21 has been synthesized and characterized by X-ray and electron diffraction, high-resolution electron microscopy, and magnetic measurements. This oxide constitutes the (alpha)= 2 ?= 1 term of the homologous series (A3B2O6)(alpha)(A3B3O9)?. Isolated rows of polyhedra sharing faces along the c-axis are made up of units of two and three face-sharing octahedra (occupied by Mn) linked by one trigonal prism (occupied by Co) in an ordered way. The chains are separated by columns of Sr atoms. This material behaves as a magnetically disordered system. The magnetic properties suggest antiferromagnetic correlations along the chains, but no long-range magnetic order is achieved.