| Abstract
| - The crystal structure of the 2H perovskite BaMnO3 has been refined from neutron powderdiffraction data collected at room temperature and 80 and 1.7 K. The structure consists ofchains of face-sharing MnO6 octahedra, separated by Ba2+ cations. At room temperature, a= 5.6991(2), c = 4.8148(2) Å, space group P63/mmc. At 80 K, a = 9.8467(1), c = 4.8075(1) Å,space group P63cm. The structural phase transition introduces a displacement of neighboringchains and reduces the coordination number of Ba2+. Long-range antiferromagnetic orderingis apparent below TN = 59(2) K, with a magnetic moment of 1.31(5) μB per Mn4+ cation at1.7 K. Neighboring spins within each chain are antiferromagnetically coupled and lie in aplane perpendicular to [001]. The spin directions associated with the chains at (1/3, 2/3, z)and (2/3, 1/3, z) are rotated by ±120° with respect to that of the chain at (0, 0, z).
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