Formation and stabilization of nanosize grains in ferromagnetic thin films by dispersed C60

Abstract

Thermal stability and formation of the nanostructured metal–C60 films have been studied. Comparative grain growth kinetic studies at 450 °C between Co–C60 and Co films show higher thermal stability and significantly slower grain growth in the Co–C60 thin film than in the Co film. Atomic force microscope observation shows that the surface of the Co film is coarsened by severe grain growth and formation of surface thermal grooves after annealing at 450 °C while the surface of the Co–C60 film remains smooth due to high thermal stability and slow grain growth in the film. A self-assembly grain growth mechanism is proposed to explain the formation of the uniform columnar nanosize grain structures in these ferromagnetic metal–C60 thin films. Estimated grain sizes based on this mechanism agree with the experimental measurement and give a relationship between the grain size and the C60 concentration in these films. These results indicate that C60 has a dual function of forming and stabilizing the nanosize grains in the metal–C60 films.