Structural and magnetic properties of micropolycrystalline cobalt thin films fabricated by direct current magnetron sputtering

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 of the films were investigated. As the sputtering power increases from 15 to 60 W, the Co thin films transition from an amorphous to a polycrystalline state, accompanied by an increase in the intercrystal pore width. Simultaneously, the resistivity decreases from 276 to 99 µΩ·cm, coercivity increases from 162 to 293 Oe, and in-plane magnetic anisotropy disappears. As the sputtering pressure decreases from 1.6 to 0.2 Pa, grain size significantly increases, resistivity significantly decreases, and the coercivity significantly increases (from 67 to 280 Oe), which can be attributed to the increase in defect width. Correspondingly, a quantitative model for the coercivity of Co thin films was formulated. The polycrystalline films sputtered under pressures of 0.2 and 0.4 Pa exhibit significant in-plane magnetic anisotropy, which is primarily attributable to increased microstress.