Preparation, crystal structure and magnetic behavior of new double perovskites Sr2B'UO6 with B'= Mn, Fe, Ni, Zn

摘要

Sr2B'UO6 double perovskites with B' = Mn, Fe, Ni, Zn have been prepared in polycrystalline form by solid-state reaction, in air or reducing conditions. These new materials have been studied by X-ray diffraction (XRD), magnetic susceptibility and magnetization measurements. The room-temperature crystal structure is monoclinic (space group P2(1)), and contains alternating B'O-6 and UO6 octahedra sharing corners, tilted along the three pseudocubic axes according to the Glazer notation a(-)a(-)b(+). The magnetic measurements show a spontaneous magnetic ordering below T-N = 21 K for B' = Mn, Ni, and T-C = 150 K for B' = Fe. From a Curie-Weiss fit, the effective paramagnetic moment for B' = Mn (5.74 mu(B)/f.u.) and B' = Ni(3.51 mu(B)/f-U.) are significantly different from the corresponding spin-only moments for the divalent cations, suggesting the possibility of a partial charge disproportionation B'(2+) + U6+ + double left right arrow B'(3+) + U5+, also accounting for plausible ferrimagnetic interactions between B' and U sublattices. The strong curvature of the reciprocal susceptibility for B' = Fe precludes a Curie-Weiss fit but also suggests the presence of ferrimagnetic interactions in this compound. This charge disproportionation effect is also supported by the observed B'-O distances, which are closer to the expected values for high-spin, trivalent Mn, Fe and Ni cations. (c) 2007 Elsevier Inc. All rights reserved.