Strong correlations produce the Curie-Weiss phase of NaxCoO2

Within the t-J model we study several experimentally accessible properties of the 2D-triangular lattice system NaxCoO2, using a numerically exact canonical ensemble study of 12 to 18 site triangular toroidal clusters as well as the icosahedron. Focusing on the doping regime of x similar to 0.7, we study the temperature dependent specific heat, magnetic susceptibility, and the dynamic Hall coefficient R-H(T,omega) as well as the magnetic field dependent thermopower. We find a crossover between two phases near x similar to 0.75 in susceptibility and field suppression of the thermopower arising from strong correlations. An interesting connection is found between the temperature dependence of the diamagnetic susceptibility and the Hall coefficient. We predict a large thermopower enhancement, arising from transport corrections to the Heikes-Mott formula, in a model situation where the sign of hopping is reversed from that applicable to NaxCoO2.