Annealing behaviour of structural and magnetic properties of evaporated Co thin films

Abstract

Cobalt thin films of 50 nm nominal thickness were e-beam evaporated on silicon substrates covered with thermal oxide. Two series of independent and cumulative vacuum annealings up to 600 ◦ C and 650 ◦ C, respectively, were performed. The x-ray diffraction, specular and non-specular x-ray reflectivity and longitudinal magneto-optical Kerr effect measurements were applied to probe the annealing behaviour of the film structure and magnetic properties. A gradual transition from the hexagonal close-packed (hcp) to the face-centred cubic (fcc) structure was observed. Evolution of the in-plane magnetic anisotropy is dominated by residual stresses which relax during the structural transformation. The coercivity follows the stress behaviour in the hcp phase up to 300 ◦ C and increases abruptly above 400 ◦ C due to improving the magneto-crystalline anisotropy in the growing fcc crystallites and enhanced surface/interface roughness. (Some figures in this article are in colour only in the electronic version)