Strong influence of a magnetic layer on the critical current of Nb bridge in finite magnetic fields due to surface barrier effect

TL;DR

This study demonstrates that a magnetic Co layer significantly enhances the critical current in Nb/Co bilayers under tilted magnetic fields due to surface barrier effects, with theoretical modeling supporting the findings.

Contribution

It provides experimental evidence and theoretical explanation for the magnetic layer's influence on critical current enhancement in Nb/Co bilayers under finite magnetic fields.

Findings

Critical current exceeds that of pure Nb in certain field orientations.

Large difference in critical currents for opposite current directions.

Theoretical model accurately explains the surface barrier effect.

Abstract

We measured the critical current of the bilayer Nb/Co in the applied magnetic field. When the magnetic field was tilted to the axis which was perpendicular to the plane of the bilayer we observed a large difference in critical currents flowing in opposite directions. We found that the largest critical current of the bilayer exceeded the critical current of the superconductor without Co layer in a wide range of the tilted magnetic fields. The theory which takes into account the surface barrier effect for vortex entry and magnetic field of the magnetic layer gave a quantitative explanation of our experimental results.