Crystal structure and magnetic properties of a new layered cobalt oxyselenide

The crystal structure and magnetic properties of a new layered cobalt oxyselenide La2Co2O3Se2 were investigated through powder X-ray diffraction, magnetic susceptibility, and specific heat measurements. This oxyselenide crystallizes in a tetragonal structure with space group I 4 / m m m which is isostructural with La2Fe2O3Se2. The lattice parameters were determined to be a = 4.0761 Å and c = 18.4488 Å . The Co ion is six-coordinated by two oxide ions and four selenide ions, forming a CoO2Se4 octahedron. On the other hand, the La ion is eight-coordinated by four oxide ions and four selenide ions, forming a LaO4Se4 decahedron. The Co2OSe2 monolayers consisting of face-sharing CoO2Se4 octahedra and the La2O2 bilayers consisting of edge, face-sharing LnO4Se4 decahedra are stacked along the c -axis. The magnetic susceptibility and specific heat of La2Co2O3Se2 indicate that the magnetic behavior of the Co2+ ions is two-dimensional and reveal that a long-range antiferromagnetic ordering occurs below 220 K. The antiferromagnetic interaction between nearest neighbor Co2+ ions is estimated to be J / k B ∼ − 28 K .