Thermodynamic properties of Na0.65CoO2

Specific heat of the layered Na0.65CoO2 powder sample over the temperature region of 3-360 K has been studied. Features hinting at charge ordering below room-temperature were observed. Magnetic phase transition at 28 K as well as signs of short-range ordering confirm the 2D character of magnetism with weak inter-planar coupling in the system. Comparison to different 2D antiferromagnetic models suggests that the magnetic lattice is more square- than triangular-like, what could be favoured by the charge ordering.12th Czech and Slovak Conference on Magnetism, Jul 12-15, 2004, Kosice, Slovaki