Defect related vortex dynamics behaviors in ‘1144’-type iron-based superconductors

Abstract We have synthesized ‘1144’- type (Ca 1 –x Pr x KFe 4 As 4 and CaKFe 4 As 4 ) and ‘122’-type (Ba 0.6 K 0.4 Fe 2 As 2 and Ba 0.6 Rb 0.4 Fe 2 As 2 ) iron-based superconductors. Based on these crystals, we have investigated the vortex dynamics of the ‘1144’- and ‘122’-type iron-based superconductors. The results indicate that the novel flux dynamics behaviors of the ‘1144’-type iron-based superconductors are closely related to their defect structures. First, the intergrowths in ‘1144’-type superconductors can function as columnar defects under an applied magnetic field H ∥ ab -plane, which results in a dip structure in the magnetization hysteresis loops (MHLs) near zero field due to the self-field effect. Second, the intergrowths, as strong pinning sites, provide a large pulling force on the flux lines and cause a small magnetization peak at temperatures below 10 K under magnetic fields from about 3–7 T in MHLs for the ‘1144’-type superconductors. Third, there may be vortex entanglement due to the presence of strong pinning centers, which impedes the elastic-to-plastic motion of vortices ( E – P phase transition) resulting in a weak second magnetization peak (SMP) effect in the bulk ‘1144’-type superconductors. Fourth, the intergrowths introduce disorder into the superconductors and accelerate the magnetic 3D-to-2D transition, which causes the thickness-dependent J c and SMP effects due to the rigidity of flux lines with decreasing sample thickness. The current results are significant for our understanding of the relationship between the flux pinning behaviors and the defect structures for a superconductor.