Anisotropic Magnetoresistance in Charge-Ordering   $Na_{0.34}(H_3O)_{0.15}CoO_2$:Strong Spin-Charge Coupling and Spin Ordering
  Angular-dependent in-plane magnetoresistance (AMR) for single crystal $Na_{0.34}(H_3O)_{0.15}CoO_2$ with charge ordering is studied systematically. The anisotropic magnetoresistance shows a twofold symmetry at high temperature with rotating H in the Co-O plane, while a sixfold symmetry below a certain temperature ($T_\rho$). At $T_\rho$, the symmetry of AMR changes from twofold to fourfold with rotating magnetic field (H) in the plane consisting of the current and c-axis. The variation of AMR symmetry with temperature arises from the subtle changes of the spin structure. These results give a direct evidence for the itinerant electrons directly coupled to the localized spins. 
C. H. Wang, X. H. Chen, G. Wu, T. Wu, H. T. Zhang, J. L. Luo, G. T.   Liu and N. L. Wang