Study of ferrite ferrofluids by small-angle scattering of polarized neutrons

Nanoparticles consisting of a magnetic core (Fe3O4, CoFe2O4 and CuFe2O4) and a hydrophobic shell were prepared by chemical co-precipitation of the inorganic cores and by subsequently modifying the surface with dodecanoic acid. The nanoparticles were then dispersed in cyclohexane to form stable ferrofluids. These dispersions were investigated by small-angle scattering of polarized neutrons and the data were interpreted according to a `pearl-necklace' model, opportunely modified to account for the core–shell structure of the particles. Results of the fitting show that the particles consist of a magnetic core with a mean radius of 40–50 Å and an organic shell with a thickness of 7–8 Å. These nanoparticles assemble in fractal aggregates when a magnetic field is applied.