Anisotropy of critical current densities in Ba1−x K x Fe2As2 and Ba(Fe1−x Co x )2As2 with splayed columnar defects

Effects of bimodal splayed columnar defects in Ba1−x K x Fe2As2 and Ba(Fe1−x Co x )2As2 single crystals through 2.6 GeV U irradiation and 220 MeV Au irradiation are investigated. Magnetic field profiles measured by magneto-optical imaging clarified the presence of in-plane anisotropy of the critical current density (J c) in 2.6 GeV U irradiated crystals, where J c parallel to the splay plane is larger than that perpendicular to the splay plane. However, the in-plane anisotropy of J c is absent in 220MeV Au irradiated crystals. Possible origin of this discrepancy is discussed based on the structure of introduced defects.