Synthesis, structural characterization, and magnetic study of Sr4Mn2CoO9

Polycrystalline Sr4Mn2CoO9 has been synthesized and characterized by X-ray and electron diffraction, high-resolution electron microscopy, and magnetic measurements. This oxide constitutes the alpha = 3, beta = 1 term of the homologous series (A(3)B(2)O(6))(alpha)(A(3)B(3)O(9))(beta). The essential feature of this structure is the presence of isolated rows of polyhedra sharing faces along the c-axis and formed by the alternation of one trigonal prism occupied by a Co cation and two Mn cations in octahedral coordination; the chains are separated by Sr atoms. The magnetic properties seem to indicate strong antiferromagnetic correlations along the chains, but no three-dimensional (3D) magnetic long range order is observed. The global magnetic behavior indicates a partially ordered system, close to a magnetic spin glass.