Magnetic anisotropies and cationic distribution in CoFe2O4 nanoparticles prepared by co-precipitation route: Influence of particle size and stoichiometry

Magnetic anisotropies and crystallographic structures of iron-cobalt nanospinels obtained with the co-precipitation synthesis process are revealed using X-ray Absorption Spectroscopy and X-ray Magnetic Circular Dichroism. The chemical process allows to obtain nanoparticles of various sizes and chemical composition, but it is the site symmetry environment of Co2+ that is found to be the crucial parameter that governs the magnetic anisotropies of the nanospinels. The distribution of Co2+ among the crystallographic sites of the structure is directly linked to the temperature of the synthesis process. In parallel, the results also revealed that a superficial rich shell of iron is formed for the iron-cobalt nanospinels stable in acidic medium leading to chemically inhomogeneous nanoparticles.