Synthesis and characterization of bimagnetic bricklike nanoparticles

Bimagnetic FePt/CoFe2O4 nanoparticles having a bricklike morphology were synthesized by growing a soft magnetic CoFe2O4 phase on FePt cubic nanoparticle seeds. The size of the soft phase could be controlled by tuning the material ratio of the FePt seeds to the CoFe2O4 component. To obtain magnetic hardening, the as-synthesized bricklike nanoparticles were annealed at elevated temperatures under a reductive atmosphere to convert the disordered face-centered cubic FePt phase into the ordered L1(0) phase having high magnetic anisotropy. When the particles were annealed, a gradual change was observed in morphology from bricklike particles to spherical polycrystalline nanocomposite particles because of diffusion. Meanwhile, the magnetic energy density was enhanced as a result of the exchange coupling between the hard and soft phases. The enhancement was dependent on the ratio of the volumes of the soft phase and the hard phase.