Synthesis, structure and magnetic properties of honeycomb-layered Li3Co2SbO6 with new data on its sodium precursor, Na3Co2SbO6

Abstract

Li₃Co₂SbO₆ is prepared by molten salt ion exchange and its structure refined by the Rietveld method confirming the honeycomb-type Co/Sb ordering of its Na precursor. Monoclinic rather than trigonal symmetry of Na₃Co₂SbO₆ is directly demonstrated for the first time by peak splitting in the high-resolution synchrotron XRD pattern. The long-range antiferromagnetic order is established at T_N ≈ 6.7 K and 9.9 K in Na₃Co₂SbO₆ and Li₃Co₂SbO₆, respectively, confirmed by both the magnetic susceptibility and specific heat. Spin-wave analysis of specific heat data indicates the presence of 3D AFM magnons in Na₃Co₂SbO₆ and 2D AFM magnons in Li₃Co₂SbO₆. The field dependence of the magnetization almost reaches saturation in moderate magnetic fields up to 9 T and demonstrates characteristic features of magnetic field induced spin-reorientation transitions for both A₃Co₂SbO₆ (A = Na, Li). Overall thermodynamic studies show that the magnetic properties of both compounds are very sensitive to an external magnetic field, thus predicting a non-trivial ground state with a rich magnetic phase diagram. The ground state spin configuration of Li₃Co₂SbO₆ has been determined by low-temperature neutron powder diffraction. It represents a ferromagnetic arrangement of moments in the honeycomb layers with antiferromagnetic coupling between adjacent layers.