Stability of the magnetoresistance for NiO-containing Co/Cu/Co spin valves naturally placed in air

The Co/Cu/Co spin valves with an additional NiO layer at the top (TSV) and under the bottom (BSV) were set in air at room temperature for about four years. Effects of time on the stability, the magnetoresistance (MR), and microstructures were investigated. Results show that the MR of TSV is more stable than that of BSV. The MR of BSV decreases 12.5% in the first 1000 days, while it increases 4% after another 360 days, while the MR of TSV keeps almost unchanged within the range of measurement error. Different time-dependent behavior of the MR value for BSV and TSV was ascribed to the different contribution of the roughness at NiO/Co and Co/Cu interfaces. PACS 68.60.Dv; 61.10.Eg; 68.35.Ct; 73.43.Qt; 75.25.+z