BaFe2(As1-xPx)2 (x = 0.22-0.42) thin films grown on practical metal-tape substrates and their critical current densities

TL;DR

This study optimizes growth conditions for BaFe2(As1-xPx)2 thin films on metal tapes, achieving high critical current densities and revealing that certain defects can enhance performance under magnetic fields.

Contribution

It identifies optimal substrate temperature and phosphorus concentration for high-quality films and uncovers the beneficial role of defects in improving critical current density.

Findings

Optimized growth at 1050°C and x=0.28 yields Tc of 26.6 K and Jc of ~1 MA/cm² at 4 K.

Higher Ts (1250°C) samples with more defects show superior Jc under high magnetic fields.

Horizontal defects like stacking faults act as vortex pinning centers, enhancing Jc.

Abstract

We optimized the substrate temperature (Ts) and phosphorus concentration (x) of BaFe2(As1-xPx)2 films on practical metal-tape substrates for pulsed laser deposition from the viewpoints of crystallinity, superconductor critical temperature (Tc), and critical current density (Jc). It was found that the optimum Ts and x values are 1050 degree C and x = 0.28, respectively. The optimized film exhibits Tc_onset = 26.6 and Tc_zero = 22.4 K along with a high self-field Jc at 4 K (~1 MA/cm2) and relatively isotropic Jc under magnetic fields up to 9 T. Unexpectedly, we found that lower crystallinity samples, which were grown at a higher Ts of 1250 degree C than the optimized Ts = 1050 degree C, exhibit higher Jc along the ab plane under high magnetic fields than the optimized samples. The presence of horizontal defects that act as strong vortex pinning centers, such as stacking faults, are a possible origin of the high Jc values in the poor crystallinity samples.