Effect of Ga and Mn doping on structural, electrical transport and magnetic properties of Na0.75CoO2

The effects of doping with magnetic Mn ions or nonmagnetic Ga ions on the structural, electrical transport and magnetic properties of Na0.75CoO2 have been investigated. It has been found that the lattice parameter c of the samples increases with Ga or Mn ion doping. Ga doping raises the electrical resistivity of Na0.75CoO2, but the metallic conducting behaviour of the compound has not been influenced. In contrast, 5% Mn doping leads to a metal-insulator transition at low temperatures in Na0.75Co1-yMnyO2. The susceptibility of the Ga doped sample shows strong magnetic field dependence, while the susceptibility of the Mn doped samples is not very sensitive to the magnetic field. This work implies that magnetic interaction plays an important role in NaxCoO2.