  New electronic phases have been identified and placed in the (T,H) phase
diagram of metallic NaxCoO2. At low Na-content (x = 0.36), the magnetic
susceptibility diverges with a power law T^(-n), n<1, and shows (T,H) scaling,
indicating the proximity to a magnetic quantum phase transition. At high Na
contents (x = 0.6) the mass of the quasiparticles does never diverge, but
renormalizes and becomes strongly field dependent at low temperatures, forming
a heavy Fermi-Liquid. Our results make superconducting NaxCoO2 a clear
candidate for magnetically mediated pairing.
