Spin-dependent tunneling with Coulomb blockade

We have fabricated ${\mathrm{C}\mathrm{o}/\mathrm{A}\mathrm{l}}_2{\mathrm{O}}_3/\mathrm{C}\mathrm{o}$ tunnel junctions in which the ${\mathrm{Al}}_2{\mathrm{O}}_3$ layer includes a unique layer of small and disconnected cobalt clusters, with a typical mean diameter ranging from 2.0 to 4.0 nm. We observe spin-dependent tunneling properties with, below about 50 K, typical Coulomb-blockade effects induced by intermediate electron tunneling into cobalt clusters. The tunnel magnetoresistance ratio is approximately the same in the Coulomb-blockade regime (low-temperature range with very high tunnel resistance) and in the room-temperature regime without Coulomb blockade. It also depends weakly on the applied voltage.