ENHANCED MAGNETORESISTANCE OF PERMALLOY AL-OXIDE/COBALT TUNNEL-JUNCTIONS IN THE COULOMB-BLOCKADE REGIME/

We report on magnetotransport properties of arrays of cobalt/aluminum- oxide/permalloy tunnel junctions with lateral dimensions in the range of 100x200 nm(2). Due to the small capacitances, these devices show si multaneously a pronounced Coulomb blockade behavior at low temperature s and spin-dependent tunneling transport. The Coulomb blockade energie s range from 0.1 to 2.6 meV. All tunnel junctions exhibiting Coulomb b lockade behavior did also show a strong dependence of the tunnel curre nt on an external magnetic field, i.e., a tunneling magnetoresistance. At temperatures below 100 K, the resistance changes up to 17% in magn etic fields of similar to 500 Oe. In addition to the known slight incr ease of the tunneling magnetoresistance with decreasing bias voltage, we found a strong enhancement in the Coulomb blockade regime. This enh ancement is explained by cotunneling effects. Considerations towards p ossible application in devices are given. [S0163-1829(98)51938-8].