POINT-CONTACT ELECTRODES TO PROBE CHARGING EFFECTS IN INDIVIDUAL ULTRASMALL COBALT CLUSTERS

A new technique to probe a single nanometer-scale magnetic particle by measuring the tunneling current through point-contact electrodes is d escribed. The tunnel junctions are formed by a bulk cobalt bottom elec trode, a monolayer of ultrasmall Co clusters sandwiched between two Al 2O3 barriers and a point-contact top electrode, defined by e-beam lith ography and permitting to study the quantum transport through an isola ted cluster. We report on single electron charging effects such as Cou lomb blockade and Coulomb staircase which are undoubtedly consistent w ith the tunneling through a single Co cluster. One of our devices exhi bits a Coulomb gap of 380 mV which is, to our knowledge, one of the la rgest values ever reported in metallic granular systems. (C) 1998 Amer ican Institute of Physics.