From FePt-Fe3O4 to L10-FePt-Fe nanocomposite magnets with a gradient interface

We report a novel approach for the fabrication of exchange-coupling L10-FePt–bcc-Fe nanocomposites with a gradient interface between hard and soft phases from FePt nanoparticles (NPs) and FePt–Fe3O4 dumbbell shaped NPs, which are prepared by a facile one-pot synthesis method. High temperature annealing in argon is first used to convert FePt in FePt–Fe3O4 dumbbell shaped NPs to the L10-FePt phase. Then Fe3O4 in FePt–Fe3O4 dumbbell shaped NPs is reduced to bcc-Fe by low temperature annealing in reducing gas, forming L10-FePt–Fe nanocomposites. The L10-FePt–Fe nanocomposites exhibit both large coercivity and high magnetic moment. The work demonstrates that creating a nanoscale gradient interface between magnetically hard and soft phases is a promising approach for the fabrication of high performance permanent magnets.