Thickness dependence of giant magnetoresistance effect in granular Cu-Co thin films

This work investigates the magnetic and transport properties of Cu-Co thin films with a special reference to their dependence on the film thickness. S uch dependencies of the giant magnetoresistance (GMR) effect in silver-base d magnetic alloys, such as Ag-Fe, Ag-Co, and Ag-FeNi films, have recently b een found, and they were interpreted within the framework of surface spin-f lipping scattering. This article reports on similar thickness dependence in the Cu-based alloy, although the spin-orbit interaction in Cu films is muc h weaker than in Ag films. A reduction of the GMR in the thinnest samples b y a factor of 6, compared to the value of as-deposited bulk samples (8.6% i n 50 kOe and at 5 K), was accompanied by an increase in resistivity by no m ore than 50%. A novel vapor-mixing technique of simultaneous sputtering fro m two sources was used to deposit Cu80Co20 granular thin films of the 20% n ominal Co volume fraction. The thickness of the films, ranging from 8 to 40 0 nm, was measured by the small-angle x-ray reflectivity method. The averag e size of the Co particles ranging from 2.5 to 3 nm was determined from the superparamagnetic behavior of the Cu-Co granular films. (C) 1999 American Institute of Physics. [S0021-8979(99)18908-4].