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

5 years ago

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

Sergio Lentijo-Mozo, Efisio Zuddas, Alberto Casu, Andrea Falqui, Davide Deiana

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 external magnetic field. This response is similar to that of an iron oxide–manganese oxide core–shell system but differs from what is observed in multiple-shell heterostructures. Finally, we report that the most external shell becomes magnetically irrelevant above the ferrimagnetic–paramagnetic transition of the manganese oxide, and the resulting magnetic behavior of the flowerlike structures is studied in depth.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b04915

DOI: 10.1021/acs.jpcc.7b04915