Reduction of the fcc to L10 Ordering Temperature for FePt Nanoparticles Containing Cu

(FePt)_1-xCu_x alloy nanoparticles were prepared by chemical-reduction of platinum acetylacetonate, iron acetylacetonate and copper acetylacetonate with 1,2-hexadecanediol as the reducing regent. As prepared, the particles have a disordered fcc structure with an average diameter of ca. 3nm. The addition of 4 % copper promotes the effect that the disordered fcc structure transforms to ordered fct phase, thereby it reduces the ordering temperature from 500degC to 400degC compared with those without any additives. The lattice parameter change of the L1₀-ordered phase suggests that the Fe sites of FePt ordered alloy are replaced by Cu. After the (FePt)₉₆Cu₄ alloy nanoparticles being annealed at 450degC for 30 min, the coercivity of the film is more than 5000Oe, while the film containing FePt nanoparticles is about 2700Oe