Experimental parameters effecting the giant magnetoresistance (GMR) of Co/Cu/Co nanostructures are investigated. The samples were fabricated using a sputtering method with varying Co layer thicknesses in vacuum, and were annealed at temperatures 200-450C for 150 minutes. GMR measurements were carried out in magnetic fields of 2500 Gauss. Apparently, a rapid 10% rise in GMR with Co layer thickness was observed between 2 - 6 nm, followed by a gradual drop along the thickness up to 20 nm. Annealing temperature has similar effect when its ascending mode attains a 24% GMR peak point at 400C beyond which the GMR starts to fall steadily to 20% at 450C. It is predicted that, the Co and Cu species become soluble to each other as they reach 400C and a solubility process is initiated between them with Co atoms gradually precipitated from the Cu matrix, thus forming the Co clusters. Due to ferromagnetic interaction occurring at temperature exceeding 400C an anti-parallel structure is established in the sample .
The GMR increases linearly with the number of bilayer, n except for (Co/Cu) x 8 due tendency of the curve to decrease between n = 5 - 8. However, it starts to rise again along the n > 8. This up-down variation is somewhat similar to periodicity, possibly due to the [Co/Cu]_n acting as a parallel shunt resistance to the sandwich structure. For a 400C annealed sample plotted on similar axes the GMR shows an upward shift and much better improvement, preferably as high as 33%. The effect of argon gas rate injected into the deposition chamber was also studied. Initially, a small rise and fall in GMR was observed, resulting in a 11% peak between the Ar gas rates 8-15 sccm, with the curve sloping down gradually until the upper limit of 30 sccm. Such a variation may be attributed to the improvement of Co and Cu crystals formed during the 10 sccm Ar rate. The results are indicative of GMR dependency on selected experimental parameters.

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