Josephson Effect in SFNS Josephson Junctions

Abstract

The critical current, IC, of Josephson junctions both in ramp-type (S-FN-S) and in overlap (SNF-FN-FNS, SN-FN-NS, SNF-N-FNS) geometries has been calculated in the frame of linearized Usadel equations (S–superconductor, F–ferromagnetic, N–normal metal). For the ramp-type structures, in which S electrodes contact directly the end walls of FN bilayer, it is shown that IC may exhibit damping oscillations as a function of both the distance L between superconductors and thicknesses dF;N of ferromagnetic and normal layers. The conditions have been determined under which the decay length and period of oscillation of IC.L/ at fixed dF are of the order of decay length of superconducting correlations in the N metal, N, that is much larger than in F film. In overlap configurations, in which S films are placed on the top of NF bilayer, the studied junctions have complex SNF or SN electrodes (N or NF bilayer are situated under a superconductor).We demonstrate that in these geometries the critical current can exceed that in ramp-type junctions. Based on these results, the choice of the most practically applicable geometry is discussed.