Antiferromagnetic coupling between surface and bulk magnetization and anomalous magnetic transport in electro-deposited cobalt film

Abstract

We report the interesting magnetic behavior of a Co film (thickness ∼350 Å) grown on Si/Ti/Cu buffer layer by electro-deposition (ED) technique. Using depth sensitive X-ray reflectivity and polarized neutron reflectivity (PNR) we observed two layer structures for the Co film grown by ED with a surface layer (thickness ∼100 Å) of reduced density (∼68% of bulk) compared to rest of the Co film (thickness ∼250 Å). The two layer structure is consistent with the histogram profile obtained from atomic force microscope of the film. Interestingly, using PNR, we found that the magnetization in the surface Co layer is inversely (antiferromagnetically) coupled (negative magnetization for surface Co layer) with the rest of the Co layer for the ED grown film. While the PNR results from a Co film of similar layered structure grown by sputtering, showed a uniform magnetization. We also showed that the depth dependent unusual magnetic behavior of ED grown Co film may be responsible for anomalous anisotropic magnetoresistance observed in low field in this film as compared to the Co film grown by sputtering. The study indicates that the interesting surface magnetic property and magneto-transport property of the ED film is caused by its unique surface morphology.