Enhancement of supercurrent through ferromagnetic materials by interface engineering

TL;DR

This study enhances supercurrent transmission in ferromagnetic Josephson junctions by interface engineering, specifically adding thin Ni layers to NiFe, resulting in a fourfold increase in supercurrent in the $$-state.

Contribution

The paper demonstrates that inserting thin Ni layers around NiFe improves supercurrent transmission without compromising magnetic switching, advancing junction controllability.

Findings

Supercurrent in Ni/NiFe/Ni trilayers is four times higher than in NiFe alone.

Magnetic switching behavior remains stable with 0.4 nm Ni layers.

Enhanced supercurrent is linked to interface spin-dependent transport properties.

Abstract

Josephson junctions containing ferromagnetic materials exhibit interesting physics and show promise as circuit elements for superconducting logic and memory. For memory applications, the properties of the junction should be controllable by changing the magnetic configuration inside the junction. To achieve good magnetic switching properties, one should choose a soft magnetic material such as NiFe (permalloy); however, NiFe exhibits poor supercurrent transmission in Josephson junctions. In this work we put thin layers of Ni on either side of the NiFe and characterize the magnetic behavior and supercurrent transmission properties of the Ni/NiFe/Ni trilayers as a function of Ni and NiFe thicknesses. Using a Ni thickness of 0.4 nm, we find that the magnetic switching behavior of the trilayers is not severely degraded relative to plain NiFe, while the maximum supercurrent in the $\pi$-state of the trilayer Josephson junctions is increased by a factor of four relative to that of NiFe junctions. We speculate that the supercurrent enhancement is due to the different spin-dependent transport properties of the Cu/Ni and Cu/NiFe interfaces.