Large transport Jc in Sn-added SmFeAsO1−xFx tapes prepared by an ex situ PIT method

SmFeAsO1−xFx possesses the highest superconducting transition temperature (Tc) among the iron-based superconductors, with a very high upper critical field and critical current density (Jc). All these are desirable for practical applications. Although tremendous progress has been made in improving the Jc values for Sr(Ba)-122 tapes or wires [1–3], the transport Jc of Sm1111 tapes or wires is still very low. Here we report on large transport critical current densities observed in Sn-added SmFeAsO1−xFx/Fe tapes produced by an ex situ powder-in-tube (PIT) method. It was found that the loss of fluorine was reduced and the intergranular coupling was enhanced in the Sn-added samples. As a result, the onset and offset Tc values for 10 wt%, 20 wt% and 30 wt% Sn-added samples were 52 K and 35 K, 53 K and 39 K, and 54 K and 41.5 K, respectively. In particular, a transport Jc as large as 22 000 A cm−2 (Ic = 160 A) at 4.2 K under self-field was achieved in 30 wt% Sn-added specimens, which is the highest value reported so far for SmFeAsO1−xFx wires and tapes. Magneto-optical imaging further showed that there were large global currents over the whole sample, which is consistent with the results obtained by the four-probe method. (paper)