Particle size reduction and enhanced diffusion of Fe and Pt atoms in FePt–C granular films by N addition

N-doped FePt–C nanocomposite films were fabricated using facing-target sputtering method under different N2 partial pressures (PN) at room temperature. Annealing at 650 8C turns the amorphous films into ordered structures. Nitrogen doping not only make the ordering of FePt particles easier than the ordering in FePt–C films, due to the enhanced diffusivity of Fe and Pt atoms, but also effectively limits the growth of the FePt particles during the thermal induced ordering, especially for the annealed films fabricated at PN = 40%, where the average size of well-isolated FePt particles is only 8 nm. The particle size reduction and the enhanced diffusion of Fe and Pt atoms can be ascribed to the desorption of doped N atoms and dissociation of Fe–N bonds during annealing. The room-temperature coercivity of the samples decreases with the PN due to the particle size reduction and thus the enhancement of the thermal agitation for small particles during the magnetizing procedure