Taito Omura | Searcharxiv

arXiv2019

Grain boundary characteristics of oxypnictide NdFeAs(O,F) superconductors

We have systematically investigated the grain boundary (GB) angle dependence of transport properties for NdFeAs(O,F) fabricated on [001]-tilt symmetric MgO bicrystal substrates. In our previous study, NdFeAs(O,F) bicrystal films showed a weak-link behaviour even at a GB angle of 6°. However, this was caused by an extrinsic effect originating from the damage to both NdFeAs(O,F) and MgO substrate by excess F-diffusion along the grain boundary. To investigate the intrinsic nature of grain boundaries, we minimized the damage to NdFeAs(O,F) and MgO by reducing the deposition temperature of NdOF over-layer needed for F-doping. The resultant NdFeAs(O,F) bicrystal films have a critical angle of 8.5°, above which Jc starts to decrease exponentially. This critical angle is almost the same as those of other Fe-based superconductors.

cond-mat.supr-con↗

arXiv2018

Fabrication of grain boundary junctions using NdFeAs(O,F) superconducting thin films

We report on the growth of NdFeAs(O,F) thin films on [001]-tilt MgO bicrystal substrates with misorientation angle theta_GB=6°, 12°, 24° and 45°, and their inter- and intra-grain transport properties. X-ray diffraction study confirmed that all our NdFeAs(O,F) films are epitaxially grown on the MgO bicrystals. The theta_GB dependence of the inter-grain critical current density Jc shows that, unlike Co-doped BaFe2As2 and Fe(Se,Te), its decay with theta_GB is rather significant. As a possible reason of this result, fluorine may have diffused preferentially to the grain boundary region and eroded the crystal structure.

cond-mat.supr-con↗