Amorphous iron–chromium oxide nanoparticles with long-term stability

•Fe–Cr oxide nanoparticles with pre-established metals ratio were obtained.•The amorphous state and its long-term stability were highlighted by X-ray diffraction.•The average diameter of dried nanoparticles was 3.5 nm, as was estimated by TEM, AFM.•In hexane dispersion, nanoparticles with diameter in the range 2.33–4.85 nm were found.•Superparamagnetic state of NPs co-exists with diamagnetism of the organic layer.

Iron–chromium nanoparticles (NPs) were obtained through the thermal decomposition of μ3-oxo heterotrinuclear {FeCr2O} acetate in the presence of sunflower oil and dodecylamine (DA) as surfactants. The average diameter of the NPs was 3.5 nm, as estimated on the basis of transmission electron microscopy and atomic force microscopy images. Both techniques revealed the formation of roughly approximated spheres with some irregularities and agglomerations in larger spherical assemblies of 50–100 nm. In hexane, NPs with diameters in the 2.33–4.85 nm range are individually dispersed, as emphasized by dynamic light scattering measurements. The amorphous nature of the product was emphasized by X-ray powder diffraction. The study of the magnetic properties shows the presence of superparamagnetic state of iron–chromium oxide NPs and the diamagnetic contribution from DA layer forming a shell of NPs.

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