| Summary: | The crystal and magnetic structures of Sr4MMn2O 9 (M=Cu, Zn) have been refined from neutron powder diffraction data. These trigonal compounds (space group P321, a=9.5918(1), c=7.8114(1)Å (Cu); a=9.5894(1), c=7.5039(1)Å (Zn)) are n=3 members of the series A 3n+3MnBn+3O6n+9, with each unit cell containing three offset [001] polyhedral chains, each of which ideally contains a 1:1 ratio of B2O9 units and MO6 trigonal prisms. In fact anti-site disorder between Mn and M is observed, and for M=Cu the cations are disordered off the center of the prism towards a rectangular face. Both compositions show 3D anti-ferromagnetic order at 1.6K, with an ordered magnetic moment of 1.91(6) (M=Cu) or 1.8(1) (M=Zn) μ B per Mn. No ordered magnetic moment was detected on the trigonal prismatic site in either compound, consistent with the observed temperature dependence of the magnetic susceptibility. © 2003 Elsevier Inc. All rights reserved.
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