Magnetic investigation of silver sheathed Sr0.6K0.4Fe2As2 superconductor

Magnetic investigation of a silver sheathed Sr0.6K0.4Fe2As2 tape prepared by ex-situ powder-in-tube technique (PIT) is reported. A transition temperature of 34.2 K was achieved. Dc magnetic measurements were performed in fields up to 14 T between 4.2 K and Tc. From hysteresis loops magnetic critical current densities Jc were determined. The tape exhibits excellent Jc performance. In low fields, the observed steep decline of Jc in increasing field is comparable to that measured in MgB2, although at a significantly lower absolute value. A kink-like crossover to a much flatter dependence at higher fields allows for a much better high field performance than that of MgB2. Such kink is also visible in the field dependence of the mean activation energies U, which were determined from magnetic relaxation measurements. The obtained U values are similar (< 40 meV at 4.2 K and 1 T) to those of Bi2212 tapes, but an order of magnitude smaller in comparison with good MgB2 wires.