A Study of Magnetoresistance of Na0.75CoO2

The transverse (I$\bot $H) and longitudinal (I//H) magnetoresistance (MR) of Na$_{0.75}$CoO$_{2 }$single crystals have been measured above and below the spin-density-wave (SDW) transition temperature T$_{SDW}$ = 22 K. While there is little effect at T $>$ T$_{SDW}$, the MR(H=constant) is positive and increases with decreasing temperature along both ab plane and c direction at T $<$ T$_ {SDW}$. Strikingly, MR(T=constant$<$ T$_{SDW})$ increases monotonically with applied field, showing no sign of saturation up to 32 tesla in all cases. Quantitative analysis and implications of the data will be reported.