SURFACE EFFECTS IN METALLIC IRON NANOPARTICLES

Nanoparticles of metallic iron on carbon supports have been studied in situ by use of Mossbauer spectroscopy. The magnetic anisotropy energy constant increases with decreasing particle size, presumably because of the influence of surface anisotropy. Chemisorption of oxygen result s in formation of a surface layer with magnetic hyperfine fields simil ar to those of thicker passivation layers, and with a ferromagnetic co upling to the spins in the core of the particles. In contrast, thicker passivation layers have a noncollinear spin structure.