The discovery of iron-based superconductors, the first non-cuprate family of superconductors with T c above 40 K, has stimulated enormous interest in the field of superconductivity since last year. This remarkable discovery not only offers the opportunity to study the origin of superconductivity, but also opens up new possibilities of application. One of the most fascinating and useful properties of superconductors is the ability to carry electrical current with zero resistance. Here, we report the successful fabrication of dense Sr 0.6 K 0.4 Fe 2 As 2 superconducting wires using the ex situ powder-in-tube (PIT) method and demonstrate a transport J c of 3750 A cm −2 at 4.2 K. The connectivity of grains was improved upon doping (Ag or Pb) and the transport property of Sr 0.6 K 0.4 Fe 2 As 2 wires was enhanced for a lead-doped sample, especially in low fields, to a best I c of 37.5 A. Our results suggest that grain boundary properties require much greater attention when looking for applications of the high-T c iron-based superconductors.
EuFe 2 As 2 is a member of the ternary iron arsenide family. Similar to BaFe 2 As 2 and SrFe 2 As 2 , EuFe 2 As 2 exhibits a clear anomaly in resistivity near 200 K. Here we report the discovery of superconductivity in Eu 0.7 Na 0.3 Fe 2 As 2 by partial substitution of the europium site with sodium. ThCr 2 Si 2 tetragonal structure, as expected for EuFe 2 As 2 , is formed as the main phase for the composition Eu 0.7 Na 0.3 Fe 2 As 2 .Resistivity measurement reveals that the transition temperature T c as high as 34.7 K is observed in this compound. The rate of T c suppression with the applied magnetic field is 3.87 T / K, giving an extrapolated zero-temperature upper critical field of 90 T. It demonstrates a very encouraging application of the new superconductors.
Nb-sheathed Sr0.6K0.4Fe2As2 superconducting wires have been fabricated using
the powder-in-tube (PIT) method for the first time and the superconducting
properties of the wires have been investigated. The transition temperature (Tc)
of the Sr0.6K0.4Fe2As2 wires is confirmed to be as high as 35.3 K. Most
importantly, Sr0.6K0.4Fe2As2 wires exhibit a very weak Jc-field dependence
behavior even the temperature is very close to Tc. The upper critical field
Hc2(0) value can exceed 140 T, surpassing those of MgB2 and all the low
temperature superconductors. Such high Hc2 and superior Jc-field performance
make the 122 phase SrKFeAs wire conductors a powerful competitor potentially
useful in very high field applications.Comment: 15 pages, 6 figure
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