Enhanced critical-current in P-doped BaFe2As2 thin films on metal substrates arising from poorly aligned grain boundaries

TL;DR

This study demonstrates that P-doped BaFe2As2 thin films grown on poorly aligned metal substrates exhibit enhanced critical current densities due to high-density grain boundaries with misorientation angles below the critical threshold, challenging the need for highly aligned substrates.

Contribution

It shows that iron-based superconductor thin films can achieve high critical currents on poorly aligned substrates, reducing fabrication constraints compared to cuprate superconductors.

Findings

Higher Jc observed on poorly aligned substrates at 4 K.

Misorientation angles less than 6 deg. are below the critical angle.

Strong pinning attributed to high-density grain boundaries.

Abstract

Thin films of the iron-based superconductor BaFe2(As1-xPx)2 (Ba122:P) were fabricated on polycrystalline metal-tape substrates with two kinds of in-plane grain boundary alignments (well aligned (4 deg.) and poorly aligned (8 deg.)) by pulsed laser deposition. The poorly aligned substrate is not applicable to cuprate-coated conductors because the in-plane alignment >4 deg. results in exponential decay of the critical current density (Jc). The Ba122:P film exhibited higher Jc at 4 K when grown on the poorly aligned substrate than on the well-aligned substrate even though the crystallinity was poorer. It was revealed that the misorientation angles of the poorly aligned samples were less than 6 deg., which are less than the critical angle of an iron-based superconductor, cobalt-doped BaFe2As2 (~9 deg.), and the observed strong pinning in the Ba122:P is attributed to the high-density grain boundaries with the misorientation angles smaller than the critical angle. This result reveals a distinct advantage over cuprate-coated conductors because well-aligned metal-tape substrates are not necessary for practical applications of the iron-based superconductors.