Structural and magnetic properties of micro-polycrystalline cobalt thin film fabricated by DC magnetron sputtering

The pure cobalt (Co) thin films were fabricated by direct current magnetron sputtering, and the effects of sputtering power and pressure on the microstructure and electromagnetic properties were investigated. The results reveal that as the sputtering power increases from 15 W to 60 W, the Co thin film transitions from an amorphous to a polycrystalline state, which is accompanied by an increase in intercrystal pore width. Concurrently, resistivity decreases by 65%, coercivity escalates from 162 Oe to 292 Oe, and the in-plane magnetic anisotropy disappears as the film transitions to a polycrystalline state. As the sputtering pressure decreases from 1.6 Pa to 0.2 Pa, there is a notable increase in grain size, along with a dramatic drop in resistivity (from 377 μΩcm to 37 μΩcm) and a significant rise in coercivity (from 67 Oe to 280 Oe), which can be ascribed to the increasing defect width. Correspondingly, a quantitative model for the coercivity of Co thin films has been formulated. In the polycrystalline films sputtered under pressures of 0.2 Pa and 0.4 Pa, significant in-plane magnetic anisotropy is observed, which is primarily attributable to increased microstress.