Study of NiO/NiFe/Cu/NiFe spin valves

We have studied the exchange coupling of antiferromagnetic NiO/ferromagnetic Ni80Fe20 bilayers, and have found the coupling strength is closely related to the crystallographic orientation of the NiO at the NiO/Ni80Fe20 interface. As the (111) of NiO, which is a parallel spin plane, becomes predominant at the interface, the coupling is enhanced. For the development of a spin-valve sandwich utilizing NiO as an antiferromagnetic (AF) layer, the configuration S/AF/F/NF/F (S = substrate, F = ferromagnetic layer, NF = nonmagnetic spacer) is more favorable for large magnetoresistance than the S/F/NF/F/AF configuration, because the former gives a high exchange field and a smooth NF spacer, resulting in an ideal antiparallel spin alignment in the sandwich during the magnetization process. Moreover, we have obtained a magnetoresistance ratio of 8% for Ni80F20 and 15% for Co at the optimum ferromagnetic layer thickness of about 50 Angstrom.