Development of very high Jc in Ba(Fe1-xCox)2As2 thin films grown on CaF2

TL;DR

This study demonstrates that substrate-induced strain significantly enhances the critical current density in Ba(Fe1-xCox)2As2 thin films, with multilayer deposition on CaF2 achieving record pinning force densities in Fe-based superconductors.

Contribution

It shows that strain from the substrate can further improve Jc beyond Tc enhancement, and reports record pinning force densities in multilayer films.

Findings

Multilayer Ba(Fe1-xCox)2As2 films on CaF2 increase Fp by over 60%.

Maximum Fp reaches 84 GN/m^3 at 22.5T and 4.2K, a record in 122 phase.

Strain effects can surpass Tc-related improvements in Jc.

Abstract

Ba(Fe1-xCox)2As2 is the most tunable of the Fe-based superconductors (FBS) in terms of acceptance of high densities of self-assembled and artificially introduced pinning centres which are effective in significantly increasing the critical current density, Jc. Moreover, FBS are very sensitive to strain, which induces an important enhancement in critical temperature, Tc, of the material. In this paper we demonstrate that strain induced by the substrate can further improve Jc of both single and multilayer films by more than that expected simply due to the increase in Tc. The multilayer deposition of Ba(Fe1-xCox)2As2 on CaF2 increases the pinning force density Fp by more than 60% compared to a single layer film, reaching a maximum of 84 GN/m^3 at 22.5T and 4.2 K, the highest value ever reported in any 122 phase.