We consider a coherent electronic transport between two ferromagnetic electrodes separated either by a metallic nanoparticle or by a conducting molecule. Correlations between electrons with opposite spins lead to the Kondo resonance, which manifests a formation of the singlet state. Although tunneling rates for electrons with opposite spin orientations are different, the conductance reaches the unitary limit in the Kondo regime. We predict a negative magnetoresistance effect, which can be observed for asymmetric magnetic junctions.

• Received 17 June 2002

DOI:https://doi.org/10.1103/PhysRevB.67.024404