Improvement of critical current properties of iron-based superconductors by controlling artificial pinning centers and defect structure

2020 Fiscal Year Final Research Report

• Project/Area Number: 19K15034
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 21050:Electric and electronic materials-related
• Research Institution: National Institute of Advanced Industrial Science and Technology
• Principal Investigator: Ishida Shigeyuki 国立研究開発法人産業技術総合研究所, エレクトロニクス・製造領域, 主任研究員 (90738064)
• Project Period (FY): 2019-04-01 – 2021-03-31
• Keywords: 臨界電流特性 / 鉄系超伝導 / 欠陥構造 / 磁束ピン止め / 粒子線照射

Outline of Final Research Achievements

The effects of introduction of artificial defects on the critical current density (Jc) of iron-based superconductors (doped BaFe2As2) were investigated using a fast neutron irradiation technique. It was found that the chemical compositions where Jc was maximized before and after irradiation was different, and that Jc in the irradiated samples was proportional to the critical temperature (Tc) to the power of 2.25. This implies that Jc is proportional to the depairing current density (Jd), and thus Jd can be extracted from Jc measurements.
In addition, the microstructure of CaKFe4As4 was observed using scanning transmission electron microscopy, and the intergrowths of CaFe2As2 and KFe2As2 were found. These intergrowths can act as effective flux pinning centers and give rise to the high Jc of CaKFe4As4.

Free Research Field

超伝導

Academic Significance and Societal Importance of the Research Achievements

鉄系超伝導体は高磁場応用材料として注目されており、臨界電流特性向上が求められている。本研究により人工欠陥の導入でJcが最大化する化学組成が変わることが明らかになり、これはJc向上の指針となる重要な成果である。加えて、Jc測定により超伝導パラメータであるJdが抽出可能であることを見出しており、応用だけでなく基礎研究でも重要な成果といえる。また、CaKFe4As4に特有の、天然の欠陥構造を見出したことは、本物質の応用ポテンシャルを裏付ける成果であり、試料の合成条件の最適化によりJc向上につながることが期待される。