Unconventional Pinning in Iron Based Superconductors of 122 Family

Abstract We report on comparative analysis of vortex pinning in Fe-based superconductors of the 122 family with different types of doping within the models proposed by Griessen et al [Phys. Rev. Let. 72 (1994)] and Dew-Hughes [Phil. Mag. 30 (1974) 293]. We found that FBS 122 superconductors with electron and hole-doping demonstrate strong pinning with position of peak maximum h p ∼ 0.3-0.45 in normalized pinning force curve vs. reduced field h=H/H irr , whereas for samples with isovalent doping (i.e. sub- stitution As for P) our analysis shows h p ∼ 0.7 indicating weak pinning. We argue that pinning in FBS with isovalent doping can be successfully described within Griessen et al δT c and δl models, while pinning in FBS 122 superconductors with electron and hole-doping shows significantly different behavior from the δT c or δl model predictions.