Investigation of the role of spin-texture on the Na0.46CoO2

We will present magnetotransport properties and their relationship to a possible chiral spin texture in ultra-thin Na$_{0.46}$CoO$_{2}$ devices in high magnetic fields. This composition exhibits a weakly insulating state, with a frustrated local spin texture, unique, among the hexagonal Na$_{x}$CoO$_{2}$ family. Previous a large large Hall effect was found for composition $x$=0.5 (M. Foo \textit{et al.}, Phys. Rev. Lett. 92, 247001 (2004)) and prior high-field studies (L. Balicas \textit{et al.}, Phys. Rev. Lett. 94, 236402 (2005).) have found the existence of a small Fermi surface in the system and a two-fold angular magnetoresistance. To date however, the Hall-conductivity has not been investigated in magnetic fields strong enough to suppress the charge-order, above 41~T. Herein, we investigate the role of local spin-texture (in the charge-ordered state) on the Hall conductance by measuring both bulk and devices with only several monolayers thick in strong magnetic fields. Our investigations under magnetic fields ($B<$60 T) show that the high resistivity charge-order region is suppressed with out-of-plane field at $B\sim $41 T with highly non-monotonic -\textit{$\rho $}$_{xy}$ with a maximum at $B\sim $27 T and rapidly decreases to zero. However, magnetization measurements show no significant features within measurement accuracy indicating that magnetization changes are small at the field-induced phase transition. Recent theoretical advances suggest that this compound exhibits a quantum Hall state coupled with spin chirality (I. Martin, C. D. Batista, Phys. Rev. Lett. 101, 156402 (2008)).