文摘
A chemical core-shell strategy is developed here for the synthesis of ferrofluids based on nanoparticles ofdifferent ferrites with different mean sizes. A heterogeneity of chemical composition, associated with asuperficial enrichment of iron, allows to obtain chemically stable ionic colloids. We propose here a core-shell model to describe the synthesized nanoparticles, which is tested by chemical and magnetic measurementsperformed at the various steps of the synthesis. The thickness of the superficial layer, rich in iron, is rangingbetween 0.4 and 1.3 nm, depending on the nanoparticle size and on the underlying ferrite. Its density is foundclose to that of maghemite, and its magnetization depends on the core ferrite. It is low with a cobalt ferritecore and larger for the three other ferrites investigated here (NiFe2O4, CuFe2O4, and ZnFe2O4). Magneticmeasurements prove that there is a strong redistribution of Zn2+ ions inside the core of the synthesizednanoparticles based on ZnFe2O4.