Josephson current in diffusive multilayer superconductor/ferromagnet/superconductor junctions

Abstract

We calculate the Josephson current in a diffusive superconductor/ferromagnet/superconductor junction, where the ferromagnetic region contains multiple layers (or domains). In particular, we study a configuration where there are two layers with an arbitrary relative in-plane magnetization orientation, and also include non-ideal interfaces and arbitrary spin-flip scattering. We study the 0-$π$ oscillations of the critical current for varying junction width $d$, and find that the $π$ state vanishes entirely when the magnetic misorientation angle of the two layers exceeds a critical angle $ϕ_c$. While $ϕ_c \to π/2$ in the limit of high temperatures, we find that $ϕ_c$ becomes smaller than $π/2$ at low temperatures compared to $T_c$. 0-$π$ oscillations are also found when varying the temperature or the misorientation angle for fixed values of $d$, and we present phase diagrams that show qualitatively the conditions for the appearance of such oscillations. We also point out how one may obtain significant enhancement of the critical current in such a system by switching the magnetization for selected values of the junction width $d$, and comment on the necessary conditions for establishing a long range triplet Josephson effect.