Dimensional crossover and anomalous magnetoresistivity in single crystals $N{a}_{x}Co{O}_2$

Abstract

The in-plane ($\ddot{I}{}_{ab}$) and c-axis ($\ddot{I}{}_c$) resistivities, and the magnetoresistivity of single crystals $N{a}_{x}Co{O}_2$ with x = 0.7, 0.5 and 0.3 were studied systematically. $\ddot{I}{}_{ab}(T)$ shows similar temperature dependence between $N{a}_{0.3}Co{O}_2$ and $N{a}_{0.7}Co{O}_2$, while $\ddot{I}{}_c(T)$ is quite different. A dimensional crossover from two to three occurs with decreasing Na concentration from 0.7 to 0.3. The angular dependence of in-plane magnetoresistivity for 0.5 sample shows a \emph{"d-wave-like"} symmetry at 2K, while the \emph{"p-wave-like"} symmetry at 20 K. These results give an evidence for existence of a \emph{spin ordering orientation} below 20 K turned by external field, like the stripes in cuprates.

4 pages, 3 figures