High-field transport properties of a P-doped BaFe₂As₂ film on technical substrate

High temperature (high-T_c) superconductors like cuprates have superior critical current properties in magnetic fields over other superconductors. However, superconducting wires for high-field-magnet applications are still dominated by low-T_c Nb₃Sn due probably to cost and processing issues. The recent discovery of a second class of high-T_c materials, Fe-based superconductors, may provide another option for high-field-magnet wires. In particular, AEFe₂As₂ (AE: Alkali earth elements, AE-122) is one of the best candidates for high-field-magnet applications because of its high upper critical field, H_c2, moderate H_c2 anisotropy, and intermediate T_c. Here we report on in-field transport properties of P-doped BaFe₂As₂ (Ba-122) thin films grown on technical substrates by pulsed laser deposition. The P-doped Ba-122 coated conductor exceeds a transport J_c of 10⁵ A/cm² at 15 T for main crystallographic directions of the applied field, which is favourable for practical applications. Our P-doped Ba-122 coated conductors show a superior in-field J_c over MgB₂ and NbTi, and a comparable level to Nb₃Sn above 20 T. By analysing the E - J curves for determining J_c, a non-Ohmic linear differential signature is observed at low field due to flux flow along the grain boundaries. However, grain boundaries work as flux pinning centres as demonstrated by the pinning force analysis.