SPIN-DEPENDENT TUNNELING WITH COULOMB-BLOCKADE

We have fabricated Co/Al2O3/Co tunnel junctions in which the Al2O3 lay er 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 sp in-dependent tunneling properties with, below about 50 K, typical Coul omb-blockade effects induced by intermediate electron tunneling into c obalt clusters. The tunnel magnetoresistance ratio is approximately th e same in the Coulomb-blockade regime (low-temperature range with very high tunnel resistance) and in the room-temperature regime without Co ulomb blockade. It also depends weakly on the applied voltage.