Nanoscale Texture and Microstructure in a NdFeAs(O,F)/IBAD-MgO Superconducting Thin Film with Superior Critical Current Properties

• Published in: ACS applied electronic materials 2021-07, Vol.3 (7), p.3158-3166
• Main Authors: Guo, Zimeng, Gao, Hongye, Kondo, Keisuke, Hatano, Takafumi, Iida, Kazumasa, Hänisch, Jens, Ikuta, Hiroshi, Hata, Satoshi
• Format: Article
• Language: English
• ISSN: 2637-6113; 2637-6113
• DOI: 10.1021/acsaelm.1c00364

This paper reports the nanoscale texture and microstructure of a high-performance NdFeAs­(O,F) superconducting thin film grown by molecular beam epitaxy on a textured MgO/Y2O3/Hastelloy substrate. The NdFeAs­(O,F) film forms a highly textured columnar grain structure by epitaxial growth on the MgO template. Although the film contains stacking faults along the ab-plane as well as grain boundaries perpendicular to the ab-plane, good superconducting properties are measured: a critical temperature, T c, of 46 K and a self-field critical current density, J c, of 2 × 106 A/cm2 at 4.2 K. Automated crystal orientation mapping by scanning precession electron diffraction in transmission electron microscope is employed to analyze the misorientation angles between adjacent grains in a large ensemble (247 grains), and 99% of the grain boundaries show in-plane misorientation angles (Δγ) less than the critical angle θ c, which satisfies one of the necessary conditions for the high J c. Comparing the columnar grain size distribution with the mean distance of the flux line lattice, the triple junctions of low-angle grain boundaries are found to be effective pinning centers, even at high temperatures (≥35 K) and/or low magnetic fields.