Hall effect in the metallic antiferromagnet Na_xCoO₂(0.72≤x≤0.90)

Abstract

We have investigated the magnetic and magnetotransport properties of Na_xCoO₂ single crystals in the heavily doped region (0.72≤x≤0.90). Both the Hall coefficient (R-H) and the susceptibility (chi) exhibit strong temperature dependence in the antiferromagnetic (AFM) as well as in the paramagnetic (PM) states. As the AFM ordering sets in, below T-N = 21 K, R-H decreases sharply with T down to similar to 10 K and then increases rapidly. The temperature and field dependence of R-H indicates the emergence of a weak ferromagneticlike phase below 10 K. In the AFM state, R-H scales linearly with chi. The observed T dependence of R-H in the PM state has been discussed in light of the theoretical model proposed for strongly correlated electrons in a triangular lattice.