Reduced-temperature ordering of FePt nanoparticle assembled films by Fe_(30)Pt_(70)/Fe_3O_4 core/shell structure

摘要

In this paper, Fe_(30)Pt_(70)/Fe_3O_4 core/shell nanoparticles were synthesized by chemical routine and the layeredrnpolyethylenimine (PEI)-Fe_(30)Pt_(70)/Fe_3O_4 structure was constructed by molecule-mediated self-assembly technique. Therndimension of core/shell structured nanoparticles was that of 4nm core and 2 nm shell. After annealing under a flow ofrnforming gas (50%Ar_2+30%H_2) for 1 h at or above 400 ℃, the iron oxide shell was reduced to Fe and diffused to Pt-rich core, which leaded to the formation of L1_0 phase FePt at low temperature. The x-ray diffraction results and magnetic properties measurement showed that the chemical ordering temperature of Fe_(30)Pt_(70)/Fe_3O_4 core/shell nanoparticles assembly can be reduced to as low as 400℃. The sample annealed at 400℃ showed the coercivity of 4KO_e with the ;rnapplied field of 1.5T. The core/shell structure was suggested to be an effective way to reduce the ordering temperature obviously.