Effective penetration length and interstitial vortex pinning in superconducting films with regular arrays of defects

TL;DR

This study compares magnetic and non-magnetic pinning centers in superconducting films, revealing how magnetic stray fields influence vortex behavior and transport properties at different magnetic field strengths.

Contribution

It demonstrates how magnetic dots can reduce penetration length and affect vortex pinning, providing insights for optimizing superconducting film performance.

Findings

Magnetic dots outperform non-magnetic ones at low fields.

Stray fields from magnetic dots reduce penetration length.

Transport properties are affected by dot separation and magnetic character.

Abstract

In order to compare magnetic and non-magnetic pinning we have nanostructured two superconducting films with regular arrays of pinning centers: Cu (non-magnetic) dots in one case, and Py (magnetic) dots in the other. For low applied magnetic fields, when all the vortices are pinned in the artificial inclusions, magnetic dots prove to be better pinning centers, as has been generally accepted. Unexpectedly, when the magnetic field is increased and interstitial vortices appear, the results are very different: we show how the stray field generated by the magnetic dots can produce an effective reduction of the penetration length. This results in strong consequences in the transport properties, which, depending on the dot separation, can lead to an enhancement or worsening of the transport characteristics. Therefore, the election of the magnetic or non-magnetic character of the pinning sites for an effective reduction of dissipation will depend on the range of the applied magnetic field.