Magnetic and electronic properties of misfit-layered cobalt oxide (Ca1-δ OH)xCoO2

The magnetic and electronic properties of non- and hole-doped samples of misfit-layered cobalt oxide (Ca1-delta OH)(x)CoO2 were investigated using the data obtained from measurements of the magnetization, specific heat, resistivity, and Seebeck coefficient. A Curie-Weiss-like behavior was observed for all samples. In a highly doped sample, a magnetic transition at 13 K and metamagnetism, due to long-range antiferromagnetic ordering, were observed. This long-range ordering coexists with a nonordered paramagnetic moment, most likely enhanced by ferromagnetic fluctuations. Large Sommerfeld constants, gamma=32 and 46 mJ mol(-1) K-2, were obtained from the specific heat of the doped samples. This indicates that a large effective mass of the carriers exists in the hole-doped phase of this compound. The observation of both the finite value of gamma and the semiconducting resistivity indicates that the carrier is localized by the Anderson localization mechanism. The Seebeck coefficient decreases with hole doping. In low temperature, the Seebeck coefficients for the doped samples exhibit abrupt enhancements with decreasing temperature, which implies an existence of pseudogap. (C) 2007 American Institute of Physics.