Comparative study of type-II superconducting properties in polycrystalline NdFeAsO0.88F0.12 prepared by different methods

Polycrystalline NdFeAsO0.88F0.12 superconductors prepared by high pressure (HP) and ambient pressure (AP) methods were comparatively studied by magnetization and transport measurements. Upper critical field Hc2, irreversibility field Hirr and the anisotropy parameter Γ were estimated from resistance transition curves. The broadening of transition width was observed, and was ascribed to both Hc2 anisotropy and superconductivity inhomogeneity of samples. Magnetic hysteresis loops (MHLs) in low fields were measured to detect the trace of weak-link behavior. The reclosed hysteresis loops in low fields indicate that there are weak links in both samples. Magnetization critical current density Jcm were derived from MHLs. Sample HP shows higher Jcm than sample AP. Direct transport I–V measurements show that the transport critical current density Jct are very low but persist up to 9 T, suggesting intrinsic strong-link existing in both samples.