Effect of interfaces on supercurrent through ferromagnetic materials

TL;DR

This paper investigates how interface materials affect supercurrent transmission in ferromagnetic Josephson junctions, demonstrating that replacing Cu/NiFe with Pd/NiFe interfaces doubles the supercurrent and alters transition behavior.

Contribution

It introduces the use of Pd/NiFe interfaces in ferromagnetic Josephson junctions, showing improved supercurrent transmission compared to Cu/NiFe interfaces.

Findings

Supercurrent increased by a factor of 2 with Pd/NiFe interfaces.

The position of the first 0-π transition shifts with interface change.

Replacing interfaces enhances supercurrent efficiency in the junctions.

Abstract

Ferromagnetic Josephson junctions exhibit fascinating physics and the potential for applications in superconducting logic and memory. The junctions in a demonstrated superconducting memory prototype contain a magnetic spin-valve structure with Ni as the fixed layer and NiFe (Permalloy) as the free layer. However, NiFe exhibits poor supercurrent transmission, which limits the efficiency of the Josephson junction. We have previously shown that the supercurrent transmission through a Cu/NiFe/Cu trilayer can be improved by adding thin layers of Ni between the Cu and NiFe -- possibly due to the advantageous spin-dependent transport properties of the Cu/Ni interfaces. In this work we explore this idea further by replacing the Cu/NiFe interfaces with Pd/NiFe, which also have more desirable transport properties. Compared to the reference junctions containing Cu/NiFe interfaces, the new junctions exhibit an increase in the $\pi$-state supercurrent by a factor of 2 along with a change in the position of the first $0-\pi$ transition.