Tailoring magnetic properties of core∕shell nanoparticles

Bimagnetic FePt∕MFe2O4(M=Fe,Co) core∕shell nanoparticles are synthesized via high-temperature solution phase coating of 3.5nm FePt core with MFe2O4 shell. The thickness of the shell is controlled from 0.5 to 3nm. An assembly of the core∕shell nanoparticles shows a smooth magnetization transition under an external field, indicating effective exchange coupling between the FePt core and the oxide shell. The coercivity of the FePt∕Fe3O4 particles depends on the volume ratio of the hard and soft phases, consistent with previous theoretical predictions. These bimagnetic core∕shell nanoparticles represent a class of nanostructured magnetic materials with their properties tunable by varying the chemical composition and thickness of the coating materials.