Josephson tunnel junctions with ferromagnetic $\Fe_{0.75}\Co_{0.25}$ barriers

TL;DR

This study investigates Josephson tunnel junctions with ferromagnetic Fe-Co barriers, revealing rapid decay and oscillation of the superconducting pair wave function influenced by strong ferromagnetism, magnetic remanence, and flux trapping.

Contribution

It provides detailed measurements of oscillation and decay lengths in Fe-Co barriers, demonstrating the effects of strong ferromagnetism on Josephson junction behavior.

Findings

Oscillation length of ~0.79 nm between 0 and π-phase coupling

Decay length of ~0.22 nm for the pair wave function amplitude

Increased magnetic remanence and flux trapping with thicker barriers

Abstract

Josephson tunnel junctions with the strong ferromagnetic alloy $\Fe_{0.75}\Co_{0.25}$ as the barrier material were studied. The junctions were prepared with high quality down to a thickness range of a few monolayers of Fe-Co. An oscillation length of $\xi_{F2}\approx 0.79\:{\rm {nm}}$ between 0 and $\pi$-Josephson phase coupling and a very short decay length $\xi_{F1}\approx 0.22\:{\rm {nm}}$ for the amplitude of the superconducting pair wave function in the Fe-Co layer were determined. The rapid damping of the pair wave function inside the Fe-Co layer is caused by the strong ferromagnetic exchange field and additional magnetic pair breaking scattering. Josephson junctions with Fe-Co barriers show a significantly increased tendency towards magnetic remanence and flux trapping for larger thicknesses $d_{F}$.