Enhancement of Magnetic Properties for FePt Nanoparticles by Rapid Annealing in a Vacuum

FePt nanoparticles with uniform compositions were synthesized by a modified coreduction process of FeCl2 center dot 4H(2)O and Pt(acac)(2) and then rapidly annealed in a vacuum under temperatures ranging from 500 to 700 degrees C. We found that the coercivities of the FePt nanoparticles were greatly enhanced by the rapid annealing in a vacuum. Negative peaks on delta M curves for the annealed FePt nanoparticles demonstrate that the predominant interparticle interactions are dipolar-type rather than exchange coupling ones, which indicates that the rapid annealing in a vacuum can prevent the agglomeration of the nanoparticles. Through the heat treatment of annealing in a vacuum, monodispersed Fe46Pt54 nanoparticles with a high coercivity of 9230 Oe were successfully fabricated.