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The metal–insulator transition in the strongly correlated layered compound NaγCoO2 induced by dilute Mn doping

Structure, transport and magnetic properties have been investigated for the layered materials NaγCo1−xMnxO2 (). With increase of the Mn concentration, the in-plane lattice parameter a decreases while the lattice parameter c increases. 3% Mn doping can result in a metal–insulator transition. The temperature dependence of the magnetization of the samples obeys the Curie–Weiss law and the effective moment of the magnetic ions increases with doping. Electron energy-loss spectroscopy measurement shows that the Co valence is about 3.3 and remains unchanged upon doping. However, the valence of Mn increases rapidly with doping and reaches 3.7 ± 0.1 for the sample with x = 0.5. The results are discussed in terms of the disorder effect induced by doping of magnetic ions. This work demonstrates that the structure, transport and magnetic properties of NaγCoO2 are very sensitive to doping with magnetic ions.