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.

Self-assembly of nanoparticles (NPs) into tailored structures is a promising strategy for the production and design of materials with new functions. In this work, 2D arrays of iron oxide NPs with interparticle distances tuned by grafting fatty acids and dendritic molecules at the NPs surface have been obtained over large areas with high density using the Langmuir-Blodgett technique. The anchoring agent of molecules and the Janus structure of NPs are shown to be key parameters driving the deposition. Finally the influence of interparticle distance on the collective magnetic properties in powders and in monolayers is clearly demonstrated by DC and AC SQUID measurements. The blocking temperature T(B) increases as the interparticle distance decreases, which is consistent with the fact that dipolar interactions are responsible for this increase. Dipolar interactions are found to be stronger for particles assembled in thin films compared to powdered samples and may be described by using the Vogel Fulcher model.

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Assemblies of magnetic nanoparticles (NPs) are intensively studied due to their high potential applications in spintronic, magnetic and magneto-electronic. The fine control over NP density, interdistance, and spatial arrangement onto substrates is of key importance to govern the magnetic properties through dipolar interactions. In this study, magnetic iron oxide NPs have been assembled on surfaces patterned with self-assembled monolayers (SAMs) of mixed organic molecules. The modification of the molar ratio between coadsorbed 11-mercaptoundecanoic acid (MUA) and mercaptododecane (MDD) on gold substrates is shown to control the size of NPs domains and thus to modulate the characteristic magnetic properties of the assemblies. Moreover, NPs can be used to indirectly probe the structure of SAMs in domains at the nanometer scale.

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Two dimensional (2D) nanoparticles (NP) assemblies have become very attractive due to their original collective properties, which can be modulated as a function of the nanostructure. Beyond precise control on nanostructure and easy way to perform, fast assembling processes are highly desirable to develop efficient and popular strategies to prepare systems with tunable collective properties. In this article, we report on the highly efficient and fast 2D assembling of iron oxide nanoparticles on a self-assembled monolayer (SAM) of organic molecules by the microwave (MW)-assisted copper(I) catalyzed alkyne−azide cycloaddition (CuAAC) click reaction. Microwave irradiation favors a dramatic enhancement of the assembling reaction, which was completed with maximum density in NPs within one hour, much faster than the conventional CuAAC click reactions that require up to 48 h. Moreover, the MWassisted click reaction presents the great advantage to preserve specific reactions between alkyne and azide groups at SAM and NP surfaces, respectively, and also to avoid undesired reactions. To the best of our knowledge, this is the first time this approach is performed to nanoparticles assembled on surfaces.

Synthesis of new heterometallic layered magnets with controlled chirality have been achieved by insertion of chiral and non-chiral salen-type Ni(II) complexes into copper and cobalt layered simple hydroxides.