Giant anisotropy of the magnetoresistance and the 'spin valve' effect in antiferromagnetic Nd2-xCexCuO4

We have studied anisotropic magnetoresistance (MR) and magnetization with a rotating magnetic field (B) within the CuO(2) plane in lightly doped AF Nd(2-x)Ce(x)CuO(4). A giant anisotropy in the MR is observed at low temperature, below 5 K. The c-axis resistivity can be tuned over about one order of magnitude just by changing the B direction within the CuO(2) plane, and a scaling behavior for the out-of-plane and in-plane MR is found. A 'spin valve' effect is proposed for explaining the giant anisotropy of the out-of-plane MR and the evolution of the scaling parameters with the external field. It is found that the field-induced spin-flop transition of the Nd(3+) layer under high magnetic field is the key to understanding the giant anisotropy. These results suggest that a novel entanglement of charge and spin dominates the underlying physics.