Effect of Co layer thickness on structural and magnetic properties of C/Co/C films

Granular C/Co/C films have been prepared by magnetron sputtering from C and Co onto glass substrates at room temperature and subsequent in situ annealing. It has been found that the structure and magnetic properties of the C/Co/C films depend strongly on the Co layer thickness. Vibrating sample magnetometer measurements indicate that the in-plane coercivities reach maximum in 20nm Co thickness of both as-deposited and annealed films. The squareness ratio of annealed films was more than 0.8. X-ray diffraction shows that majority Co nanograins are formed as the hexagonal-close-packed (HCP) structure in 20nm Co thickness with annealing at 400°C. Scanning probe microscope was used to scan surface morphology and magnetic domain structures. The values of the surface roughness were lower than 0.6nm in all annealed samples. The average magnetic cluster size was estimated to be about 10nm in annealed 20nm Co thickness films.