Faceting effect on magnetism in manganese ferrites nanoparticles

Manganese ferrite (MnFe2O4) stands out among multifunctional spinel ferrites for its attractive magnetic properties, high chemical stability and excellent biocompatibility, which are essential prerequisites for effective performance in various applications, including biomedical. However, very little work has been carried out on the ideal reaction conditions to obtain nanoparticles with high performance in terms of magnetization correlated to facet engineering. This study reports the synthesis of MnFe2O4 nanoparticles by a thermal decomposition process, controlling the decomposition temperature and the ligand/precursor ratio. Indeed, with a decomposition temperature of manganese stearate maintained at 270 °C and a ligand/precursor ratio equal to 2, superparamagnetic behavior and significantly high saturation magnetization were obtained from monodisperse nanoparticles of cubic shape and approximately 7 nm in size. Combining magnetic measurements with Monte Carlo simulations demonstrated that this behavior is attributed to the shape anisotropy of cubic nanoparticles, which favors the orientation of the magnetic moment along planar facets with low surface anisotropy. The strong influence of this faceting on the nanomagnetism of ferrite based on MnFe2O4 should open new avenues for numerous applications, particularly in biomedical imaging.