Bimagnetic nanoparticles with enhanced exchange coupling and energy products

Bimagnetic FePt / Fe 3 O 4 nanoparticles with core/shell or heterodimer structure have been prepared using a sequential synthetic method. The dimension of both FePt and Fe 3 O 4 was tuned by varying the synthesis parameters. The as-synthesized bimagnetic nanoparticles were superparamagnetic at room temperature. After being annealed in a reducing atmosphere, the FePt / Fe 3 O 4 bimagnetic nanoparticles were converted to a hard magnetic nanocomposite with enhanced energy products due to the exchange coupling between the hard and soft magnetic phases. It was found that the exchange coupling in nanocomposites made from the core/shell nanoparticles is stronger than that from the heterodimer nanoparticles. By tuning the dimensions of the FePt and Fe 3 O 4 phases, the energy product up to 17.8 MG Oe was achieved in the annealed nanocomposites, which is 36% higher than the isotropic single-phase FePt counterpart.