Palladium: A localised paramagnetism

We report on the origin of ferromagnetic like behaviour observed for 2.4 nm size Pd nanoparticles. Localised magnetic moments on metallic surfaces have been recently shown to induce orbital motion of the itinerant electrons via spin-orbit coupling. As a result of this coupling the magnetic anisotropy is enhanced and the surface magnetic moments can be blocked up to above room temperature. Since Pd has been customary treated as a paradigmatic itinerant system, localisation of magnetic moments at its surfaces was not initially expected. However, it is shown, through the experimental thermal dependence of both magnetic susceptibility and Hall resistance, that magnetism of bulk Pd, is a localised paramagnetism and, consequently, can give rise to permanent magnetism at its surface. Such surface permanent magnetism is experimentally observed only when the percentage of surface moments is outstanding as is the case for nanoparticles.