Giant magnetoresistance and microstructure of Co-Cu and FeCo-Cu granular films

Co-Cu and FeCo-Cu granular films were prepared by DC (or RF) magnetron sputtering and post-deposition annealing. The influence of annealing conditions (temperature, duration) on GMR has been investigated systematically. It is found that the cumulative isothermal annealing at an optimal temperature (moderately high) promotes the precipitation of magnetic grains but limits their excessive growth, and therefore, leads to more homogenous and smaller particles, which is in favor of the GMR improvement. By a combined study of TEM, magnetization and GMR, it is believed that the GMR in these granular films mainly originates from the spin-dependent scattering of conducting electrons in the surfaces between magnetic particles and Cu matrix; especially, the very fine particles with a diameter of a few nm may be most effective for spin-dependent scattering.