Upper critical field of the 122-type iron pnictide superconductors Original Research Article

The upper critical fields (H c2) of the single crystals (Sr,Na)Fe2As2 and Ba0.55K0.45Fe2As2 were determined by means of measuring the electrical resistivity, ρxx(μ0H)ρxx(μ0H), using the facilities of pulsed magnetic field at Los Alamos. In general, these compounds possess a very large upper critical field (Hc2(0)) with a weak anisotropic effect. The detailed curvature of Hc2(Tc) may depend on the magnetic field orientation and the sample compositions. We argue that such a difference mainly results from the multi-band effect, which might be modified via doping.