Core-shell structure of chemically synthesised FePt nanoparticles: a comparative study

We carried out solution synthesis of FePt nanoparticles through different chemical methods, using four "hot soap methods", i. e. particle formation in the presence of surfactant molecules at high temperatures, and one polyol process. Structural and magnetic properties of the as-made particles pointed to a core-shell structure for the particles prepared with hot soap methods, with an iron-depleted core surrounded by a pure iron shell. Such a structure has an impact on the magnetic properties of as-made particles since Fe atoms from the shell are oxidised and non magnetic. We proved however that iron atoms of this shell are available during the formation of the ordered phase upon annealing: L1(0) phase for small particles, L1(2) for bigger ones. In contrast, the core-shell structure was not observed in the case of nanoparticles synthesised according to the polyol process. This outlines the key role of the stabilising ligands, long alkyl chain surfactants in the former case and tetraethylene glycol in the latter.