Simple test for high Jc and low Rs superconducting thin films

TL;DR

A simple magnetic fishing method using a Nd-Fe-B magnet effectively identifies high-Jc, low-Rs superconducting thin films at 77 K, providing a cost-effective alternative to complex testing procedures.

Contribution

This paper introduces a straightforward magnetic fishing technique to quickly assess high critical current density and low surface resistance in superconducting thin films.

Findings

Nd-Fe-B magnet can fish out high-Jc Tl-1223 films.

Fished films have lower Rs than YBCO films.

Non-fishable films exhibit high Rs values.

Abstract

A simple method, fishing high-Tc superconductor thin films out of liquid nitrogen bath by a permanent magnet (field > Hc1) due to the effect of high flux pinning, has been suggested to identify films having high critical current density (Jc > 106 A/cm2 at 77 K) and thus a low microwave surface resistance (Rs). We have demonstrated that a Nd-Fe-B magnet, having a maximum field of ~ 0.5 T, could fish out Tl-1223 superconducting thin films on LSAT substrate with a thickness of ~ 5000 Angstrong having Jc > 1 MA/cm2 (at 77 K) whereas it could not fish out other films with Jc < 0.1 MA/cm2 at 77 K. The fished out films exhibit Rs values 237 - 245 ((at 77 K and 10 GHz, which is lower than that (Rs = 317 (() of the best YBCO film at the same temperature and frequency. On the other hand, the non-fishable films show very high Rs values. This method is a very simple tool to test for high Jc and good microwave properties of superconducting films of large area which otherwise require a special and expensive tool.