Magnetic Properties of Nanocrystalline Co Thin Films Grown on Glass

Co thin films have been deposited by sputtering on glass substrates. The film thickness ranges from 10 to 170 nm. Structural results show that the films are polycrystalline with a dominant hcp structure. An ultrafine distribution of crystallites with diameters about 5 nm is found for the thinnest samples, which is also detected by a smooth surface. The grain size grows as the thickness increases in consequence an evolution occurs from a well-defined uniaxial anisotropy to a more isotropic behavior. This gives rise to an increase in the coercivity, domain wall pinning strength, and its dispersion. The magnetization reversal mechanism is also influenced by the film thickness. Using transverse susceptibility measurements we have found that the maximum domain wall pinning strength increases significantly as the film thickness increases.