Characterization of Cu additive FePt–C granular films

FePt–C granular films doped with different Cu atomic fractions (xCu) were fabricated using facing-target sputtering at room temperature and subsequently annealed at 650 8C. Structural analyses reveal that the as-deposited films are in amorphous state. Appropriate Cu addition (xCu = 14) can improve the ordering of L10 FePt phase, and excessive Cu doping destroys the formation of ordered L10 phase with the appearance of Fe3C and CuPt phases. Besides, preferential graphitization of amorphous carbon (a-C) occurs near large metal particles upon annealing. Annealing turns the as-deposited superparamagnetic films into ferromagnetic associated with coercivity peaks at xCu = 14, drops from 11.2 kOe at 5 K to 7.2 kOe at 300 K in a 50 kOe field