Annealing effect on magnetoresistance in NiO-Co-Cu based spin valves

We have fabricated two sets of NiO-Co-Cu based spin valves by the magnetosputtering technique with different deposition parameters. Magnetoresistance (MR) measurements show that the MR value for the NiO layer under the bottom of Co/Cu/Co spin valve (BSV) is larger than that for the NiO layer at the top of Co/Cu/Co (TSV). The MR value of BSV decreases with increasing annealing temperature in air or in vacuum, which disappears at the blocking temperature of NiO, i.e., about 250 °C. There is maximum MR value for TSV annealing at a temperature range from room temperature to 350 °C. The different thermal behavior for BSV and TSV is explained by the competition between the interface roughness of NiO/Co, which was determined by the grazing incident X-ray reflectivity and X-ray diffuse scattering, and the coupling effect between Co layer and NiO layer.