On the novel double perovskites A(2)Fe(Mn0.5W0.5)O-6 (A= Ca, Sr, Ba). Structural evolution and magnetism from neutron diffraction data

摘要

New A(2)Fe(Mn0.5W0.5)O-6 (A = Ca, Sr, Ba) double perovskite oxides have been prepared by ceramic techniques. X-ray diffraction (XRD) complemented with neutron powder diffraction (NPD) indicate a structural evolution from monoclinic (space group P2(1)/n) for A = Ca to cubic (Fm-3m) for A = Sr and finally to hexagonal (P6(3)/mmc) for A = Ba as the perovskite tolerance factor increases with the A(2+) ionic size. The three oxides present different tilting schemes of the FeO6 and (Mn,W)O-6 octahedra. NPD data also show evidence in all cases of a considerable anti-site disordering, involving the partial occupancy of Fe positions by Mn atoms, and vice-versa. Magnetic susceptibility data show magnetic transitions below 50 K characterized by a strong irreversibility between ZFC and FC susceptibility curves. The A = Ca perovskite shows a G-type magnetic structure, with weak ordered magnetic moments due to the mentioned antisite disordering. Interesting magnetostrictive effects are observed for the Sr perovskite below 10 K. (C) 2018 Elsevier Masson SAS. All rights reserved.