Post-synthesis heat treatments of g-Fe2O3 nanoparticles embedded in a refractory matrix: From annealing of structural defects to doping

International audienceMagnetic nanoparticles (NPs) synthesized by low-temperature routes often present structural disorder, from extended defects to local rearrangements related to vacancy order or inversion in spinel ferrites. Post-synthesis heat treatments of preformed particles embedded in a refractory matrix are shown to modify magnetic anisotropy, either by annealing of crystal defects or by doping, while preserving the mean size and size distribution of the initial colloid. Such protected annealing of g-Fe2O3 NPs allows a large and tunable increase of the anisotropy constant upon cobalt doping, using a two-step protocol that may involve adsorption of Co(II) ions at the surface of g-Fe2O3 NPs followed by their dispersion in a silica matrix and heat treatments up to 600 C