High-field transport properties of a P-doped BaFe 2 As 2 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 Nb ₃ Sn 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, AEFe ₂ As ₂ (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 BaFe ₂ As ₂ (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 10 ⁵  A/cm ² 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 MgB ₂ and NbTi, and a comparable level to Nb ₃ Sn 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.