Large transport critical currents and magneto-optical imaging of textured Sr1-xKxFe2As2 superconducting tapes

We report the temperature dependence of the transport critical current density (Jc) in textured Sr1-xKxFe2As2/Fe (Sr122) tapes fabricated by an ex situ powder-in-tube process. Critical currents were measured in magnetic fields up to 0-15 T and/or the temperature range 4.2-30 K by using a dc four-probe method. It was found that textured Sr122 tapes heat-treated at low temperatures showed higher transport Jc performance due to much improved intergrain connections. At temperatures of 20 K, easily obtained using a cryocooler, Jc reached ~ 10^4 A/cm^2 in self field, which is the highest transport value of ferropnictide wires and tapes reported so far. Magneto-optical imaging observations further revealed significant and well distributed global Jc at 20 K in our tapes. These results demonstrate that 122 type superconducting tapes are promising for high-field applications at around 20 K.