COULOMB-BLOCKADE AND ENHANCEMENT OF MAGNETORESISTANCE CHANGE IN ULTRASMALL FERROMAGNETIC TUNNEL-JUNCTIONS

Coulomb blockade and negative magnetoresistance of ultrasmall ferromag netic tunnel junctions are studied based on the Feynman path integral approach. It is shown that the change in magnetoresistance is consider ably enhanced in the Coulomb blockade regime. This is due to the nonli near current-voltage characteristics caused by the higher-order tunnel ing processes which set in since negative magnetoresistance tends to m ake Coulomb blockade unstable. Results obtained are qualitatively in g ood agreement with recent experimental findings. Coulomb blockade and the magnetoresistance in ultrasmall ferromagnetic double junction are also discussed briefly. (C) 1998 Elsevier Science B.V. All rights rese rved.