  122 type pnictide superconductors are of particular interest for high-field
applications because of their large upper critical fields Hc2 (> 100 T), low
Hc2 anisotropy r (< 2), and high thin-film critical current densities Jc (> 1
MA/cm2 at 4.2 K). Successful magnet applications require fabrication of
polycrystalline superconducting wires that exhibit large in-field Jc, which is
limited by poor grain coupling and weak-link behavior at grain boundaries. Here
we report our recent achievement in the developing Sr0.6K0.4Fe2As2 tapes with
transport Jc up to 0.1 MA/cm2 at 10 T and 4.2 K. This value is by far the
highest ever recorded for iron based superconducting wires and has surpassed
the threshold for practical application for the first time. The synergy effects
of enhanced grain connectivity, alleviation of the weak-link behavior at grain
boundaries, and the strong intrinsic pinning characteristics led to the
superior Jc performance exhibited in our samples. This advanced Jc result opens
up the possibility for iron-pnictide superconducting wires to win the race in
high-field magnet applications.
