Synthesis, structure and magnetic properties of La3Co2SbO9: A double perovskite with competing antiferromagnetic and ferromagnetic interactions

The synthesis, structural characterization, and magnetic properties of La3Co2SbO9 double perovskite are reported. The crystal structure has been refined by X-ray and neutron powder diffraction data in the monoclinic space group P2(1)/n. Co2+ and Sb5+ have the maximum order allowed for the La3Co2SbO9 stoichiometry. Rietveld refinements of powder neutron diffraction data show that at room temperature the cell parameters are a=5.6274(2) angstrom, b=5.6842(2) angstrom. c=7.9748(2) angstrom and beta=89.999(3)degrees. Magnetization measurements indicate the presence of ferromagnetic correlations with T-c=55 K attributed to the exchange interactions for non-linear Co2+-O-Sb5+-O-Co2+ paths. The effective magnetic moment obtained experimentally is mu(exp)=438 mu(B) (per mol Co2+), between the theoretical one for spin only (3.87 mu(B)) and spin-orbit value (6.63 mu(B)). indicating partially unquenched contribution. The low magnetization value at high magnetic field and low temperature (1 mu(B)/f.u., 5 T and 5 K) and the difference between ZFC and FC magnetization curves (at 5 kOe) indicate that the ferromagnetism do not reach a long range order and that the material has an important magnetic frustration. (C) 2012 Elsevier Inc. All rights reserved.