Giant Magnetoresistance in Co/Cu Multilayers Prepared by Vacuum Evaporation and Sputtering Methods

Co/Cu multilayer films were deposited on glass substrate by both vacuum evaporation and sputtering methods. Pure Cu films were also prepared by the same methods. The surface morphology and resistivity were investigated in order to determine the influence of the preparation methods on the film structure. The MR ratio oscillates with the Cu layer thickness dCu in sputtered multilayer films prepared at low Ar pressure (15 mTorr), whereas it increases monotonically with dCu in sputtered multilayer films prepared at high Ar pressure (50 mTorr). On the other hand, the MR ratio oscillates with dCu only beyond 20Å in evaporation-deposited multilayer films prepared at a high deposition rate (2Å/s). The MR ratio of the samples prepared at a low deposition rate (0.5Å/s) is nearly zero. AFM observations of the multilayer and Cu films indicated the existence of a rumpling of the layered structure, with a fluctuation period of 100 to 500Å. The fluctuation of the rumpling is large in multilayer films evaporation-deposited at a low rate (0.5Å/s) and small in multilayer films sputter-deposited at low pressure (15 mTorr). The difference in the MR ratios of samples prepared by the two methods and under different conditions is mainly due to the differences in multilayer stacking structures.