Alternative mechanism of the sign-reversal effect in superconductor-ferromagnet-superconductor Josephson junctions

TL;DR

This paper proposes a new explanation for the sign-reversal effect in superconductor-ferromagnet-superconductor Josephson junctions, attributing it to phase modulation caused by domain magnetization rather than nonmonotonic critical current density.

Contribution

It introduces a model where domain magnetization induces phase modulation, providing an alternative mechanism for the sign-reversal effect in SFS Josephson junctions.

Findings

Phase modulation can cause sign changes in the critical current.

The effect depends on the ratio of magnetic flux in domains to flux quantum.

This mechanism explains oscillations of critical current with layer thickness or temperature.

Abstract

We consider a simple model of a multidomain superconductor-ferromagnet-superconductor (SFS) Josephson junction. Sign-alternating magnetization $M$ in domains leads to a spatial modulation of the phase difference $\phi (x)$. Due to this modulation the Josephson critical current $I_{c}$ may have a different sign depending on the ratio of the magnetic flux in a domain, 4$\pi Ma(2d_{F}),$ to the magnetic flux quantum. This phase modulation, but not a nonmonotonic dependence of the local critical current density $j_{c}$, may be the reason for oscillations of the current $I_{c}$ {\bf \}as a function of the F layer thickness $2d_{F} $ or temperature, observed in experiments.