Crystal and Magnetic Structures of 2H BaMnO₃

The crystal structure of the 2H perovskite BaMnO 3 has been refined from neutron powder diffraction data collected at room temperature and 80 and 1.7 K. The structure consists of chains of face-sharing MnO 6 octahedra, separated by Ba 2+ cations. At room temperature, a = 5.6991(2), c = 4.8148(2) Å, space group P 6 3 / mmc . At 80 K, a = 9.8467(1), c = 4.8075(1) Å, space group P 6 3 cm . The structural phase transition introduces a displacement of neighboring chains and reduces the coordination number of Ba 2+ . Long-range antiferromagnetic ordering is apparent below T N = 59(2) K, with a magnetic moment of 1.31(5) μ B per Mn 4+ cation at 1.7 K. Neighboring spins within each chain are antiferromagnetically coupled and lie in a plane 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 ).