Introducing the monoclinic polymorph of the Kitaev magnet Na$_{2}$Co$_{2}$TeO$_{6}$

Abstract: Recent theoretical studies have suggested that the low-energy Hamiltonian of honeycomb cobaltate systems could be dominated by anisotropic Kitaev interactions. Motivated by the theory, a honeycomb layered material Na${2}$Co${2}$TeO${6}$ with a hexagonal unit cell has been studied and found to exhibit antiferromagnetic (AFM) ordering at 27 K with two spin reorientation transitions at 15 and 5 K. Here we report a monoclinic polymorph of Na${2}$Co${2}$TeO${6}$, also with honeycomb layered structure but with a single AFM transition at 9.6 K and without spin reorientation transitions at lower temperatures. Using neutron diffraction, we identify an in-plane zigzag AFM order in the ground-state with the spins canted out of the honeycomb planes and ferromagnetically coupled between them. The zigzag order is suppressed by a magnetic field of 6 T.