Synthesis, structure and magnetic properties of La _3Co _2SbO _9: A double perovskite with competing antiferromagnetic and ferromagnetic interactions

摘要

The synthesis, structural characterization, and magnetic properties of La _3Co _2SbO _9 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. Co ~2 and Sb ~5 have the maximum order allowed for the La _3Co _2SbO _9 stoichiometry. Rietveld refinements of powder neutron diffraction data show that at room temperature the cell parameters are a=5.6274(2) ?, b=5.6842(2) ?, c=7.9748(2) ? and β=89.999(3)°. Magnetization measurements indicate the presence of ferromagnetic correlations with T _C=55 K attributed to the exchange interactions for non-linear Co ~2-O-Sb ~5-O-Co ~2 paths. The effective magnetic moment obtained experimentally is μ _(exp)=4.38 μ B (per mol Co ~2), between the theoretical one for spin only (3.87 μ _B) and spin-orbit value (6.63 μ _B), indicating partially unquenched contribution. The low magnetization value at high magnetic field and low temperature (1 μ _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.