On the magnetic structure of DyNiO3

The crystallographic structure of DyNiO3 has been investigated at T = 200, 100, and 2 K from high-resolution neutron powder diffraction (NPD) data. We show that the Structure is monoclinic, space group P2(1)/n, front the metal-insulator transition temperature at T-MI = 564 K down to 2 K. The Ni atoms occupy two different sites 2d (Ni1) and 2c (Ni2), whose valences, estimated from bond-valence consideration, are +2.43(1) and +3.44(1) at 2 K, respectively. This is interpreted as the result of a partial charge disproportionation of the type 2Ni(3+) -> Ni1((3-delta)+)+Ni2((3+delta)+), with delta approximate to 0.55 at T = 2 K. The magnetic structure has been studied from a NPD pattern at T = 2 K, well below the establishment of the antiferromagnetic (AFM) ordering at T-N = 154 K, as well as from sequential data collected from 16 K down to 2 K. The magnetic order is defined by the propagation vector k = (1/2,0,1/2). Two possible magnetic structures are compatible with the magnetic intensities. In the second solution both Ni sublattices participate in the magnetic order, as well as Dy since it corresponds to a total disproportionation of Ni3+ to Ni2+ and Ni4+. In the second Solution both Ni sublattices participate in the magnetic order. as well as Dy. The magnetic moments for Nil and Ni2 atoms at T = 2 K are 1.8 (2) and 0.8 (2) mu(B), respectively. These values are also compatible with a partial charge disproportionation. Dy3+ ions exhibit long-range magnetic ordering below 8 K An abrupt contraction of the unit-cell volume is observed at this temperature, due to a magnetoelastic coupling. The magnetic moment for Dy3+ at T = 2 K is 7.87 (6) mu(B). (C) 2009 Elsevier Inc. All rights reserved.