Water-induced two-dimensional Kondo-like scattering in Na_(0.23)CoO_2 single crystals

摘要

An in-plane Kondo-like resistivity minimum is found with a corresponding temperature T_(min), around 7 K for hydrated Na_(0.23)CoO_2 single crystals. Below 7 K, the resistivity exhibits logarithmic temperature dependence of α lnT, where α is independent of the external magnetic field up to 8 T. The feature .is resulted in terms of the Kondo-like effect arising from the presence of spin disorder induced by water intercalation in the a-b plane. Our results indicate that the water intercalation weakens the coupling between the CoO_2 layers and increases the two-dimensional characteristic of transport properties. The dependence of resistivity minimum on applied field proved also the suppression of localized Co(l) site on paramagnetic triangular superlattice. Further, the present experiments give the evidence of a more complex cooperative phenomena involving charge or spin ordering in the CoO_2 layers as a dominating factor for the understanding of hydrated Na_xCo_2 compounds.