Enhancement of corrosion resistance and superparamagnetic property by structural modulation in (Co-DLC)/DLC multilayered nanocomposite films

A structure of {[(Co-DLC)/DLC]X}n Multilayered Nanocomposite Films (MNF) is designed by inserting pure DLC high-resistance layers into Co-DLC nanocomposite film, which consists of alternating Co-DLC and DLC layers were prepared by magnetron sputtering. The electrochemical behavior and magnetic property of the films are modulated by varying the number of deposition cycles (n) and the thickness of one single-cycle (X). The electrochemical results show that this MNF structure significantly improves the corrosion resistance of the films owing to the clear interfaces, which block the micropores penetrating the films. Compared to the co-sputtering film, as the number of cycles n increases to 7, the corrosion resistance is enhanced by one order of magnitude from 2.3 × 104 to 2.2 × 105 Ω·cm2. However, the interfaces between the Co-DLC and DLC layer become blurred when the thickness of one single-cycle X is lower than 30 nm, and the corrosion resistance decreases to 3.7 × 104 Ω·cm2. In terms of magnetism, the multilayer structure helps to regulate the homogeneity of Co particle size. As X increases from 30 to 100 nm, the Co particle size increases from 2.7 to 4.7 nm, and the saturation magnetization intensity (Ms) of superparamagnetic property in the films increases from 2.8 to 8.2 mT. As X increases, the remanent magnetization ratio (Mr/Ms) decreases and reaches 0.011 at X = 100 nm, which is about one order of magnitude smaller than that of the co-sputtering film. This result indicates that the MNF have better superparamagnetic property. It is noteworthy that {[(Co-DLC)/DLC]X}n MNF with X ranging from 100 to 40 nm and n ranging from 3 to 7 can achieve high corrosion resistance and superparamagnetic property, simultaneously.