Magnetite particles with an average size of 39 nm and good monodispersity have been synthesized by coprecipitation at 70 °C from ferrous Fe2+ and ferric Fe3+ ions by a (N(CH3)4OH) solution, followed by hydrothermal treatment at 250 °C. The magnetite nanoparticles before the hydrothermal step display an average size of 12 nm and are highly oxidized when they are in contact with air. Complementary microstructural and magnetic characterizations of nanoparticles after hydrothermal treatment show unambiguously that they consist of magnetite with only a slight deviation from stoichiometry (δ ≈ 0.05), leading to Fe2.95O4.

The effect of surface inorganic-organic interactions on magnetic and structural properties of iron oxide magnetic nanoparticles functionalized by lipophilic stilbene molecules has been investigated. The molecules have been grafted through either phosphonate or carboxylate coupling agents. Mo ¨ssbauer spectra recorded at 300 and 77K suggest a global composition of Fe 2.82 O 4 for the two types of functionalization. Complementary in-field Mo ¨ssbauer and SQUID measurements have demonstrated that the nanoparticles consist in a magnetite core surrounded by an oxidized layer. The oxidized shell exhibits a spin canting in the carboxylate case leading to a decrease of the net magnetization of the oxide nanoparticle. No canting occurs in the phosphonate case, and the magnetic properties are therefore preserved. The magnetic properties thus depend on the coupling agent, e.g., surface interactions. This result is of primary importance to tune the magnetic properties of functionalized nanoparticles for biomedical and high density storage media applications.