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 ≤ft|({d)/(H)_{c2}(c}}{{d}T) right| d H c 2 c d T at greater than 4 T K-1, resulting in an anomalous increase in the anisotropic ratio γ = {{H}_{{c}2}}({ab}) H c 2 ab / {{H}_{{c}2}}({c}) H c 2 c 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.
- Publication:
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Superconductor Science Technology
- Pub Date:
- December 2019
- DOI:
- 10.1088/1361-6668/ab4f44
- Bibcode:
- 2019SuScT..32l5014X
- Keywords:
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- iron-based superconductors;
- thin films;
- vortex;
- nanorods;
- oxide doping