Interface structures in FePt/Fe3Pt hard-soft exchange-coupled magnetic nanocomposites

Self-assembly of FePt and Fe3O4 nanoparticles of different sizes led to various FePt–Fe3O4 nanocomposites. Annealing the composite under reducing atmosphere at 650 and 700 °C induced magnetically hard FePt phase and magnetically soft Fe3Pt phase. The FePt and Fe3Pt phases were either linked by a common interface or coexisted within one grain as domains with sizes <10 nm. This ensures the effective exchange coupling of magnetically hard and soft phases. High-resolution transmission electron microscopy studies provide detailed structural characterization for the FePt based nanocomposites.