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

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 P21/n), and contains alternating B′O6 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 TN=21 K for B′=Mn, Ni, and TC=150 K for B′=Fe. From a Curie–Weiss fit, the effective paramagnetic moment for B′=Mn (5.74 μB/f.u.) and B′=Ni(3.51 μB/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+⇔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′single bondO distances, which are closer to the expected values for high-spin, trivalent Mn, Fe and Ni cations.