Thickness and composition dependences of magnetic and magnetoresistive properties of CoxAg100-x alloys thin films

In granular thin films consisting of small particles of magnetic metal dispersed in nonmagnetic matrix both magnetization and magnetoresistance phenomena are directly related, and their relationship is very complex. This is due to the distribution of ferromagnetic grains in nonmagnetic metallic matrix and its mutual magnetic interactions. In this paper, we studied influence of CoxAg100-x film composition and thickness on film structure, magnetization and magnetoresistance. It has been found that the size of Co grains correlates with the sample thickness for the films with d = 20 nm, and the superparamagnetic state of Co granules is preserved up to x <= 55 at.%. However, thicker samples are superparamagnetic only up to x < 32 at.%. It is found that in granular films the GMR ratio increases with the film thickness. In addition, the dependence of the magnetization versus film thickness indicates that the microstructure of the thin films differs from that of the thicker films. The application of the Levinshtein percolation theory showed the qualitative agreement with the results of our experiment.