Building Composite Iron–Manganese Oxide Flowerlike Nanostructures: A Detailed Magnetic Study

Abstract

Here we show that it is possible to produce different magnetic core–multiple shell heterostructures from monodisperse Fe3O4 spherical magnetic seeds by finely controlling the amount of a manganese precursor and using, in a smart and simple way, a cation-exchange synthetic approach. In particular, by increasing the amount of precursor, we were able to produce nanostructures ranging from Fe3O4/manganese ferrite core–single-shell nanospheres to larger, flowerlike Fe3O4/manganese ferrite/Mn3O4 core–double-shell nanoparticles. We first demonstrate how formation of the initial thin manganese ferrite shell determines a dramatic reduction of the superficial disorder in the starting Fe3O4, bringing nanomagnets with lower hardness. Then, the growth of the second and most external manganese oxide shell causes magnetic hardening of the heterostructures, while its magnetic exchange coupling with the rest of the heterostructure can be either antiferromagentic or ferromagnetic, depending on the strength of the applied e...