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Co-Diamond Like Carbon (Co-DLC) nanocomposite film is considered as a potential biosensor material owing to its various properties such as corrosion resistance and superparamagnetic property. In this work, by adjusting the substrate temperature from 298 to 673 K, the microstructure of Co-DLC nanocomposite film is modulated. With the rising of the substrate temperature, Co particle size increases from 3.8 to 6.4 nm and the crystallinity is improved; the sp2/sp3 ratio of the film is increased, which reduces micropores for penetration of corrosive entities. As a result, the saturation magnetization of superparamagnetic property is enhanced by 2.4 times from 0.11 to 0.26 T, and the total corrosion resistance of the film is enhanced by more than 300 times from 3.5 × 104 to 1.1 × 107 Ω·cm2. By establishing the mechanism model, the improvement of magnetic properties and corrosion resistance caused by microstructure controlling in Co-DLC nanocomposite film is reasonably explained. [Display omitted] • Large Co particle size and high crystallinity induced by high substrate temperature • Reduced micropores for corrosive entities penetration by increased sp2 clusters • 2.4-time superparamagnetic magnetization and 300-time corrosion resistance realized • High magnetic properties and corrosion resistance achieved simultaneously [ABSTRACT FROM AUTHOR]

To realize the potential application of the Co-DLC magnetic nanocomposite film in biosensor, it is necessary to obtain superparamagnetic property with high magnetization and good corrosion resistance in Co-DLC film. However, the cobalt carbide produced in the traditional preparation process will deteriorate the superparamagnetic property of Co-DLC film. To suppress the formation of cobalt carbide, strong magnetic target co-sputtering has been induced to prepare the Co-DLC nanocomposite films in this work. The results show that the cobalt particles are distributed in the amorphous DLC matrix. Most of cobalt exists in the form of metallic cobalt, and no cobalt carbide is formed during the film deposition process. The films maintain superparamagnetic property, which fits well with the Langevin equation. The saturation magnetization of the Co-DLC films increases with the increase of cobalt content, which reaches 0.068 T at cobalt content of 36 at. %. Meanwhile, when the cobalt content increases, the degree of graphitization of the film increases, which leads to a decrease in corrosion resistance of the film. Whereas, the polarization resistance of Co-DLC nanocomposite film is still higher than 1.03 × 105 Ω·cm2. The Co-DLC nanocomposite films with cobalt content between 29 and 36 at. % exhibit superparamagnetic property with high saturation magnetization and corrosion resistance. [Display omitted] • The method of strong magnetic target co-sputtering inhibits the formation of cobalt carbides in Co-DLC films successfully. • These films maintain superparamagnetic property, which is fitted well with Langevin equation. • The corrosion resistance of the Co-DLC film is above 10 times higher than that of the cobalt film. • The films with cobalt content between 29 and 36 at. % exhibit both high saturation magnetization and corrosion resistance. [ABSTRACT FROM AUTHOR]