Magnetic and structural features of theNdNi1 − xMnxO3 perovskite series investigated by neutron diffraction

Abstract

Selected members of the perovskite seriesNdNi1 − xMnxO3 (0 ≤ x ≤ 1) have beenprepared by a soft chemistry technique, followed by thermal treatments either under high oxygen pressure(x ≤ 0.5) orin air (x > 0.5). The crystal and magnetic structures have been studied by means of neutrondiffraction, complemented with magnetic susceptibility measurements. Forx = 0.25, 0.75, the crystal structure of the perovskites can be defined in the orthorhombicPbnm spacegroup, with Ni and Mn distributed at random over the octahedral sites of the structure. In contrast, thex = 0.5 compound crystallizesin a monoclinic P 21/n structure containing two different octahedral positions, occupied by Niand Mn, respectively. This is a result of the charge disproportionation ofNi3 + + Mn3 + to giveNi2 + + Mn4 + cations. TheNi2 + O6 octahedra are considerablylarger than the Mn4 + O6 octahedra. This compound can be considered as a double perovskite of compositionNd2NiMnO6. UnlikeNdNiO3 andNdMnO3,which exhibit an antiferromagnetic ordering at low temperatures, the intermediate samples forx = 0.25,0.50, 0.75 exhibit a ferromagnetic arrangement of (Ni, Mn) spins, with the moments aligned along thez axis, as probed using neutron diffraction. A maximumTC of 200 K is observedfor x = 0.5, whereasTC = 150 K and 130 K areobserved for x = 0.25 and 0.75,respectively. While NdNiO3 is metallic above 200 K, a semiconducting behavior is determined between 120–300 K for theintermediate compositions.