Synthesis of Fe3O4@CoFe2O4@MnFe2O4 trimagnetic core/shell/shell nanoparticles

We report the synthesis and characterization of original 'multishell' magnetic nanoparticles made of a soft core (magnetite) covered with two successive shells: a hard one (cobalt ferrite) and then a soft one (manganese ferrite). Our results show that contrary to expectations from simple models in which the coercivity of a bimagnetic core/shell nanoparticle depends simply on the proportion of soft and hard phases within that particle, the addition of a second shell made of a soft ferrite material enhances the coercivity. Taking into account the interactions between the shells themselves and the core may thus be necessary to understand the magnetic properties of such nanoparticles.