Effects of Gd211 Ball-Milled by Stainless-Steel on Trapped Field of GdBaCuO Bulk

RE-Ba-Cu-O (REBCO, RE: rare earth element) superconducting bulk is a compact source of tesla-class magnetic field and has potential applications in compact NMR spectrometers, motors, drug delivery, etc. To operate the REBCO bulk magnets at high temperatures around 40–50 K, the enhancement of the trapped field is necessary, for which fine RE
$_{{\text{2}}}$
BaCuO
$_{{\text{5}}}$
(RE211) is quite effective. Fine RE211 was obtained by ball-milling using ZrO
$_{{\text{2}}}$
media which has excellent wear resistance and low contamination. However, a small amount of impurities is known to act as pinning centers; therefore, we prepared the fine Gd211 powder by ball-milling using a stainless steel container and balls. Single grain GdBCO bulks were fabricated by top-seeded melt growth method from a mixture of GdBa
$_{{\text{2}}}$
Cu
$_{{\text{3}}}$
O
$_{{\text{7}}-x}$
(Gd123), ball-milled Gd211, and CeO
$_{{\text{2}}}$
powders; we also used non-ball-milled Gd211 for a reference. A trapped field at 40 K increased from 3.96 T of the bulk using non-ball-milled Gd211 to 4.29 T of that using the ball-milled one, although a decrease in the
$T_\mathrm{c}$
was observed for the latter bulk. The obtained results can be explained by dilute doping of iron derived from the stainless steel media.