Vortex pinning properties in Co-doped BaFe2As2 thin films with a high critical current density over 2 MA cm−2 at 9 T

Abstract

Similar to other high-temperature superconductors, the pinning centers largely determine the critical current density (Jc) in Co-doped BaFe2As2 (Ba122:Co). Therefore, understanding the vortex pinning mechanism of high-Jc Ba122:Co thin films is important for the applications of Ba122:Co. Herein we report the pinning of the naturally grown defects in Ba122:Co thin films with a high critical current density. The transport Jc of thin films is up to 2.6 MA cm−2 in 9 T at 4.2 K, which is the highest value in iron-based superconductors. Microstructure investigations reveal a high density of ab-planar defects (stacking faults) and localized vertical defects present in the sample. The Dew–Hughes mode analyses prove that pinning centers by surface defects and by point defects are responsible for H//ab and H//c, respectively. Therefore, the high Jc in strong magnetic field for both H//ab and H//c are related to surface and point defects which act as the pinning centers in Ba122:Co films.