Abstract

Cobalt (Co) films prepared by radio frequency (RF) sputtering for 5 to 55 min were studied by atomic force microscopy (AFM) and vibrating sample magnetometry. The root mean square surface roughness quantified from 1 ´ 1 µm² AFM images tended to increase with increasing sputtering time above 20 min. Compared to hysteresis loops in the case of perpendicular magnetic field, the ferromagnetic Co films of thickness ranging between 120 and 400 nm exhibited smaller saturation field and larger maximum susceptibility when the applied magnetic field was parallel to their surface as a result of the in-plane anisotropy. In the case of thickness over 300 nm, both in-plane and perpendicular magnetizations were markedly increased, whereas the electrical resistance was substantially decreased because of surface oxidation and the geometric alignment of the grains. Since the increase in thickness over 300 nm only enhanced the coercive field in the case of perpendicular magnetization, the coercive field was likely influenced by the elongated grain grown perpendicular to the film surface.

Key words: Radio frequency (RF) sputtering, magnetic thin film, cobalt, atomic force microscopy (AFM), vibrating sample magnetometry (VSM).