Josephson effect in superconductor/ferromagnet-normal/superconductor structures

Abstract

The critical current IC of superconductor/ferromagnet-normal/superconductor (S/FN/S) Josephson junctions is calculated in the framework of linearized Usadel equations. The dependence of IC on the distance L between superconductors and thicknesses dF,N of ferromagnetic and normal layers is analyzed. It is shown that IC(L,dF) may exhibit damping oscillations as a function of both arguments. The conditions have been determined under which the decay length and period of oscillation of IC(L) at fixed dF are on the order of decay length of superconducting correlations in the N metal, ξN, that is much larger than in F film. We demonstrate also that the positions of the points L=Ln, at which IC=0 exhibit damping oscillations as a function of dF. The number of transitions from 0 to π states in IC(L, dF) increases under L→Ln. Outside these narrow intervals of L around Ln sign and value of IC are independent on dF for dF≳ξF. This fact is important for possible applications of S/FN/S Josephson junctions and S/FNF/S spin valve Josephson devices.