Magnetic properties of transition-metal nanoclusters on a biological substrate

We have investigated the magnetic properties of transition-metal clusters with a single grain size of about 1 nm. These metallic nanoclusters have been deposed on a biological substrate. This substrate is a purified self-assembling paracrystalline surface layer (S-layer) of the Bacillus sphaericus strain JG-A12 which exhibits square symmetry and is composed of identical protein monomers. First data of the magnetic susceptibility, taken in a SQUID magnetometer at 0 < B < 7 T and 1.8 K < T < 400 K, reveal unusual magnetic properties. The Stoner enhancement factor of the d conduction-electron susceptibility in the Pd and Pt nanoclusters is dramatically reduced compared to the one of the corresponding bulk transition metals. The weakened magnetism of the 5d electrons is considered to play a crucial role for the occurrence of superconductivity in microgranular Pt by adjusting the balance between electron-phonon interaction and competing magnetic interactions.
Keywords: metallic nanoclusters, paracrystalline protein surface layer, magnetism of transition-metal nanoclusters