Probing enhanced spin lifetime through magneto-Coulomb effects in isolated nanometer size metallic clusters

We experimentally study spin injection and spin dependent transport in a single non magnetic nanoparticle contacted by ferromagnetic leads through alumina barriers. Theoretical studies on the interplay of discrete charging and spin polarised current in such a structure predict spin accumulation effects in the nanoparticle, leading to novel effects such as tunnel magnetoresistance oscillations versus bias voltage. We report the first experimental observation of spin accumulation in Au and Cu single nanoparticles of few nanometers in diameter. Fabrication is carried out using a conductive tip AFM with real time monitoring of the conductance during the nanoindentation process. With this technique, we can contact a single isolated particle of a few nanometer in size. Because the capacitance of the nanoparticle is very small, the energy needed to add an electron on it becomes larger than the thermal energy leading to discrete voltage jumps of e/C in the I-V characteristics called Coulomb blockade "staircases". The 4.2K I-V curves, showing typical Coulomb blockade transport through a unique nanoparticle, are in excellent agreement with simulations.