Crystal Growth and the Magnetic Properties of Na₂Co₂TeO₆ with Quasi-Two-Dimensional Honeycomb Lattice

Single crystal Na2Co2TeO6 has been successfully grown by self-flux method, and its lattice structure and basic magnetic properties were characterized. As determined by single crystal X-ray diffraction, Na2Co2TeO6 belongs to space group P6322 (182) with a = b = 5.2709(2) Å, c = 11.2615(15) Å, and V = 270.95 (4) Å3, the crystal structure is a layered honeycomb formed by CoO6 octahedra and the TeO6 octahedra in the center of the honeycomb layers, and the NaO6 octahedra are between the honeycomb layers. Magnetic susceptibility measurements indicate that the single crystal sample displays a distinct anisotropic behavior and the spin parallels the honeycomb plane (ab-plane). In a lower temperature region, a series of antiferromagnetic-like (AFM-like) phase transitions were observed, which may result from the spin reorientation of Co2+ ions. The different magnetization behavior between the polycrystalline structure and the single crystal (with the magnetic field parallel to and perpendicular to the ab-plane) reveals obvious magnetic anisotropy of single crystal Na2Co2TeO6. The special honeycomb planes formed by CoO6 octahedra and the AFM interaction inter- and intra-honeycomb planes may lead to the obvious anisotropy and complicated magnetic phase transitions.