Critical current densities and vortex dynamics in Ba(FeCo)As single crystals

Tamegai, Tsuyoshi*; Taen, Toshihiro*; Tsuchiya, Yuji*; Nakajima, Yasuyuki*; Okayasu, Satoru  ; Sasase, Masato*

Superconducting properties are evaluated for high-quality single crystals of Ba(FeCo)As in a wide range of doping levels. The critical current density, , in an optimally-doped crystal (Tc 24 K) shows a fishtail effect with its value over 10 A/cm even at 5 T below 10 K. Magneto-optical imaging has clarified rather homogeneous supercurrent flow in the crystal, in spite of a large amount of impurities. In the heavy-ion irradiated sample, the presence of columnar defects are confirmed and has been enhanced by a factor of five at low temperatures, reaching 6 10 A/cm at 2 K under zero field. Flux creep rate in the heavy-ion irradiated sample has been reduced in accordance with the enhancement of .