In order to make a comparison to the previous transport studies on both coupled and uncoupled sandwiches, it interesting to examine the dependence of the spin-valve MR on individual layer thickness. Figure 3 shows the variation of the AMR and spin-valve MR with Co thickness. The linear thickness dependence of the AMR is expected and is due simply to the increase of the amount of ferromagnetic material in the sample. On the other hand, the non-monotonic form of the spin-valve magnetoresistance cannot be simply explained. The broad peak is similar to that observed by Dieny et al. in their exchange-biased sandwiches.[3] Further investigation of this thickness dependence is underway, as is a detailed study of the variation of the spin-valve effect with Cu and Fe thickness.
In conclusion, the spin-valve magnetoresistance has been observed in a new sandwich system, Fe-Cu-Co. The large (> 3%) MR reproducibly achievable in polycrystalline films on silicon and glass at applied fields of only 100 Oe may have technological significance. The spin-valve magnetoresistance and its associated magnetization curve are suppressed by interlayer interdiffusion, as indicated by a growth temperature study. The variation of the spin-valve MR with Co thickness may be a clue to its fundamental origin.
We thank D. King for the x-ray measurements. This research was supported by DARPA and ONR.