We have studied the effect of an artificially intermixed region grown at the interfaces of Co/Cu spin valves with uncoupled layers. Two different structures are used: exchange-biased spin valves and engineered spin valves in which two layers are antiferromagnetically coupled and a third layer, on top of this system, is not coupled to the other two. It is shown that structural effects, induced by variation of the deposition parameters and by the intermixing can play an important role. Since the present study uses sputtered layers an intrinsic initial intermixing of 4-5Å is already present. For both types of spin valves Gp, ΔG and ΔR/R all show a gradual decrease when the nominal thickness of the total intermixed region is enlarged from 0 to 36Å. Also when the initial degree of intermixing is decreased by sputtering at higher Arpressure, Gp, ΔG and ΔR/R still show a gradual decrease as a function of intermixed layer thickness. Combined with the fact that there is no difference between an intermixed region of thickness t at one Co/Cu interface or intermixed regions of thickness t/2 at two interfaces, this indicates that the electron scattering in the intermixed region is predominantly spin independent, although this region preserves a magnetic moment.
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It is tempting to try to use something like ΔMR = α + β ln(t / τ) to find a characteristic time; however, due to the properties of the log function, this results in ΔMR = [α - ln(τ)] + β ln(t) where the quantity in square brackets is just a constant Thus the “characteristic time” is folded into the constant a.
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Willekens, M., Rijks, T., Swagten, H. et al. Effects of Interface Intermixing on the Magnetoresistance of Spin Valves with Uncoupled Co-Layers. MRS Online Proceedings Library 384, 391–396 (1995). https://doi.org/10.1557/PROC-384-391