New ferromagnetic La3Co2TaO9 double perovskite: Structural and magnetic properties

Abstract

The new double perovskite La3Co2TaO9 has been prepared by a solid-state procedure. The crystal and magnetic structures have been studied from X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD) data. Rietveld refinements were performed in the monoclinic space group P21/n. The structure consists of an ordered array of alternating B′O6 and B″O6 octahedra sharing corners, tilted along the three pseudocubic axes according to the Glazer notation a-b-c+. Rietveld refinements show that at RT the cell parameters are a=5.6005(7) Å, b=5.6931(7) Å, c=7.9429(9) Å and β=89.9539(7)°, and the refined crystallographic formula of this "double perovskite" can be written as La2(Co)2d(Co1/3Ta2/3)2cO6. Magnetization measurements and low-temperature NPD data show that the perovskite is a ferromagnet with TC=72 K. At high T it follows the Curie-Weiss law with an effective magnetic moment of 3.82μB per Co ion which is very close to spin only Co2+ (HS).