Vortex dynamics in K- and Co-doped BaFe2As2 superconducting films

by Myeongjun Oh (MS Candidate)

Wednesday Nov 18, 2015, 1:25 PM → 1:50 PM Asia/Seoul

216-1호 (제1과학관)

The industrial use of superconductors is steadily increasing despite mechanical difficulties with installation, maintenance, and operation. New types of superconducting wire are demanded because of the performance limitations of current superconducting wires. In order to increase the critical current density to a credible value, the vortex dynamics must be analyzed. The Lorentz force is exerted on vortices with the application of an electrical current, which causes energy loss in the form of electrical resistance through movement away from the pinning center. Thus, pinning vortices at pinning centers is important. In this study, we analyzed the vortex dynamics of chemical-doped BaFe2As2(Ba122) thin films.
There are high expectations for the practical application of the BaFe2As2(Ba122) superconductor to be realized because of its isotropic superconducting properties. We concentrated on two types of chemical doping of the Ba122 system: potassium and cobalt. The transition temperature (Tc) was found to fluctuate in the potassium-doped Ba122 film, and the mean free path was found to fluctuate in the cobalt-doped film. An artificial pinning center was found to have a crucial role in the doped Ba122 thin films.
The potassium-doped Ba122 film was developed ex situ by pulsed laser deposition (PLD) because of the high volatility of potassium. Plain and textured films were fabricated depending on the thickness of the precursor. Transport and electron probe microanalyzer (EPMA) measurements were performed. The textured film was observed to have a higher activation energy than the plain film. Additional pinning forces come from δTc-pinning with the textured topography, which creates fluctuations in Tc.
A homogeneous cobalt-doped Ba122 film was fabricated in situ. We inserted non-superconducting layers as artificial pinning centers. Precise measurements of the current density were performed on a 5 μm × 150 μm bridge fabricated by laser cutting and a focused ion beam (FIB). We scaled the pinning force results and concluded that core interaction occurs while the surface and point pins are dominant. The nature of the pinning center is normal.

Thesis Advisor: Prof. Younjung Jo