Magnetic properties of Co/Ag core/shell nanoparticles prepared by successive reactions in microemulsions

Co nanoparticles with an Ag covering layer have been prepared by successive reactions in microemulsions. Their magnetic behavior was studied as a function of heat treatment. It was confirmed that, under the experimental conditions of this study, the size of the Co nuclei is limited by the reactant concentration, whereas the Ag covering is fixed by microemulsion droplet size. The as-prepared particles contain mainly Co3O4 nuclei, and present high effective moments that agree with the spin state of Co3+. The observed magnetic behaviors were explained taking into account the intra- and inter-particle structural evolution of the particle assemblies annealed under different experimental conditions.