Verification of Ferromagnetism in Au Nanoparticles with Clean Surface

Au nanoparticles, which are kept in vacuum after the preparation by gas evaporation method, show ferromagnetism. We observed the increase in spontaneous magnetization up to 18.3 % after exposure to the air. This suggests that the decay of surface magnetization with adsorption of oxygen brings about the increase in total magnetization of Au nanoparticle. This is consistent with the core-shell magnetic structure in which the surface magnetization is antiparallel to the magnetization in core region.