Fabrication and Superconducting Properties of 19-Filamentary Sr 0.6 K 0.4 Fe 2 As 2 /Ag/Monel Composite Wires and Tapes

Developing multi-filamentary 122-type iron pnictides with high mechanical strength and large filling factor is essential for promoting engineering application. In this work, we fabricated 19-filamentary Sr 0.6 K 0.4 Fe 2 As 2 /Ag/Monel composite wires and tapes through employing roller-die drawing. The introduction of Monel outer sheath strongly reinforces the microhardness Hv up to 134–138, which is ~ 3.4 times higher than silver inner matrix of only 36–44. Importantly, multi-filamentary design and extraordinary microhardness of Sr 0.6 K 0.4 Fe 2 As 2 /Ag/Monel conductors increase their filling factors by a factor of 2–4 times; those are 35.6–36.4% comparing with 8–15% for the present multi-filamentary wires. Through magnetic characterization, the critical current density J c values of Sr 0.6 K 0.4 Fe 2 As 2 wires and tapes are 2.7 × 10 3 and 4.2 × 10 3 A/cm 2 at 4.2 K and 5 T, respectively. The J c enhancement in tapes is attributed to high mass density and grain texture in the filaments. Moreover, the magnetic J c exhibits weak field-dependent in the high-field region even at 20 K.