C-axis superconducting performance enhancement in Co-doped Ba122 thin films by an artificial pinning center design

Abstract

1% mol and 3% mol Y2O3 oxide particles were introduced into Co-doped BaFe2As2 (Ba122) thin films on CaF2 (00l) single crystal substrates by pulsed laser deposition to enhance the superconducting performance. They behave as amorphous nanorods oriented along the c-axis of the Co-doped Ba122 matrix, as revealed by the transmission electron microscope (TEM) measurements, and serve as strong c-axis pinning centers. The transport critical current density Jc reaches a value of ∼3.9 MA cm−2 in self-field at 4.2 K and a significant enhancement in c-axis Jc, much higher than the ab-plane Jc, was also observed due to those nanorods, suggesting that the extrinsic pinning strength by nanorods exceeds that of the ab-plane. It is surprising that the nanorods can significantly improve the thermal activation energies for vortex motion parallel to the c-axis to greater than those parallel to the ab-plane, and simultaneously reduce the superconducting transition width of the c-axis to less than that of the ab-plane at medium and low fields, implying a reduction in the thermal fluctuation in the vortex system. More importantly, the nanorods enhance the slopes at greater than 4 T K−1, resulting in an anomalous increase in the anisotropic ratio γ = / with decreasing temperature. The pinning mechanism and evolution of the relative strength of the ab-plane pinning, and correlated pinning with temperature and field, are discussed.