Fabrication of CoPt nanoparticles with high coercivity on a polymer film

L10 structured CoPt nanoparticles were fabricated on a polyimide film by depositing a 1.7-nm-thick Co–Pt alloy film, followed by annealing at 650–800 °C during which the Co–Pt alloy film was converted into a monolayer of 4 nm sized L10 phase CoPt particles. In order to produce well-separated larger particles, multiple depositions of 1.7-nm-thick Co–Pt alloy film were carried out. Heterogeneous nucleation on the pre-existing CoPt nanoparticles allowed the film deposition and annealing to be repeated up to four times to increase the average particle size from 4 nm to 7 nm as needed. The monolayer of 7-nm-szied CoPt nanoparticles exhibited a high coercivity of 9.8 kOe with a remanence ratio of 0.72. The method can be easily extended to a large area as well as other material systems to create a monolayer of metal nanoisland structures on a polymer film.