Crystal and magnetic structure of the orthorhombic perovskite YbMnO 3

Huang, Y.H. , Fjellvåg, H. , Karppinen, M. , Hauback, B.C. , Yamauchi, H. , Goodenough, J.B.
Chemistry of materials, Vol. 18, no. 8 (18 April 2006), 2130-2134
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The perovskite polymorph of YbMnO3 has been revisited. The orthorhombic phase is obtained through a high-pressure (HP) reconstructive transformation from the hexagonal sol-gel-synthesized YbMnO3 by means of HP annealing at 5 GPa and 1100 °C. Neutron powder diffraction shows that the HP form crystallizes in the orthorhombic space group Pbnm. At 298 K, the refined values for lattice parameters a, b, and c are respectively 5.2208(3), 5.8033(3), and 7.3053(4) Å. The average Mn-O-Mn angle is 141.9°, indicative of a strong tilting of the MnO6 octahedra. Magnetic susceptibility measurements indicate antiferromagnetic order of Mn3+ spins at TN = 43 K and of Yb3+ spins at 4 K. The magnetic structure is commensurate Ay with an ordered moment 3.45(5) μB at 9 K. The magnetic susceptibility obeys the Curie-Weiss law, χ = C/(T - θ), in two temperature regions, that is, above 240 K and 6-30 K. The obtained effective paramagnetic moments μeff are 6.37 μB and 4.83 μB for the two temperature ranges, respectively. The former is attributed to a superposition of paramagnetic Mn3+ and Yb3+ spins while the latter reflects primarily the paramagnetic Yb3+ moments. Re-entry of Ay magnetic ordering requires a reconsideration of the factors that contribute to the competitive spin-spin interactions on the MnO3 array. © 2006 American Chemical Society.
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