Fabrication and Characteristic of<tex>$rm Ho$</tex>-123 Coated Conductors

Abstract

We have developed <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$ Ho Ba_2 Cu_3 O_7- x$</tex> ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$ Ho$</tex> -123) coated conductors on flexible metal tape substrates. Oxide buffer layers such as YSZ and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$ CeO_2$</tex> have been deposited on textured Ni-alloy tapes. A basic technique of the formation of buffer layer was investigated, and hetero-epitaxial buffer layer of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$ CeO_2/ YSZ/ CeO_2$</tex> showed excellent in-plane alignment with the delta phi value in the range of 5 to 7 degrees. Surface roughness (Ra) of 3rd buffer layer was several nm and the surface was almost flat with few particles. Ho-123 deposition was conducted on the buffer layers by PLD method. Sample less than 0.2 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$mu m$</tex> in thickness of superconducting layer showed Jc (77.3 K, self field) over 4 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$ MA/ cm^2$</tex> . Sample with 1.3 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$mu m$</tex> in thickness of superconducting layer showed Jc (77.3 K, self field) was 1.8 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$ MA/ cm^2$</tex> near 2 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$ MA/ cm^2$</tex> and Ic (77.3 K, self field) was 231 A/cm-width. SEM photograph of Ho-123 layer revealed relatively smooth film morphology with some particles. This demonstrated fine epitaxial Ho-123 growth on <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$ Ce O_2/ YSZ/ Ce O_2$</tex> textured Ni-alloy tape. Furthermore, Jc-B characteristics at 4.2 K under the high magnetic field up to 30 T were evaluated. Ic (4.2 K, 30 T) was over 2,000 A/cm-width when the external magnetic field was applied parallel to the tape surface.