  REBa2Cu3O7-d (RE123, RE: rare earth) is one of the high-temperature
superconductors with a transition temperature (Tc) exceeding 90 K. Because of
its high Tc and large critical current density (Jc) under magnetic fields,
RE123 superconductors have been expected to play a key role in
superconductivity application. To accelerate application researches on
RE123-based devices, further improvements of Jc characteristics have been
desired. In this study, we investigated the effects of high-entropy alloying at
the RE site on the superconducting properties, through the measurements of
local (intra-grain) Jc (Jclocal) by a remanent magnetization method. We found
that Jclocal shows a trend to be improved when four or five RE elements are
solved at the RE site, which results in high configurational entropy of mixing
(delta_Smix). Because high-entropy alloying can improve Jclocal of RE123
superconductors by modification of the RE site composition and delta_Smix, and
the technique would be applicable together with other techniques, such as
introduction of nanoscale disorders, our entropy-engineering strategy
introduced here would be useful for development of RE123 superconducting
materials available under high magnetic fields.
