Magnetic Pd nanoparticles: Effects of surface atoms

We have investigated the magnetic properties of trioctylphosphine (TOP)-stabilized monodisperse palladium nanoparticles of 2, 3, 5 and 10 nm in size, in order to study the possible effects of surface Pd atoms. These nanoparticles display clear signatures of ferromagnetism such as hysteresis and saturation magnetization over the entire temperature range studied here from 2 to 380 K. The magnetization of the nanoparticles increases with decreasing particle size, indicating a possibly important role played by Pd atoms on the surface of the nanoparticles. More importantly, we also found that the magnetization of our TOP-stabilized Pd nanoparticles is one order of magnitude smaller than those of other Pd nanoparticles reported so far, which is most likely to be due to the weak nature of interface interaction between TOP ligands and Pd nanoparticles compared to other ligands. This observation is consistent with the view that the magnetism of Pd nanoparticles is strongly influenced by the interaction of surface atoms with the ligands. We discuss our experimental findings in terms of a charge transfer mechanism due to a covalent bond of Pd atoms with the protective TOP ligand, which would increase the 4d density of states of Pd atoms due to localization by the bonded P atoms.