Significant Improvement of Superconducting Properties in Nano‐NiFe ₂ O ₄ ‐Doped Y–Ba–Cu–O Single‐Grain Superconductor

Introduction of refined second‐phase particles in superconducting YB a 2 Cu 3 O 7− x (Y‐123) matrix is known to be an effective route to improve the δ l ‐type pinning and the performance of Y–Ba–Cu–O ( YBCO ) single‐grain superconductors, while the δ T c ‐type pinning induced by spatial fluctuations in matrix composition is also important and contributes to the in‐field J c performance and high‐field applications of bulk superconductors. In this communication, chemical doping of nano‐sized NiFe 2 O 4 (mean size 50 nm) in single‐grain YBCO superconductor is performed using a novel top‐seeded infiltration growth ( TSIG ) technique based on a solid source pellet ( SSP ) of nano‐Y 2 O 3 + BaCuO 2 . The results indicate that, significant improvement of bulk performances including levitation force (33.93 N) and trapped field (0.3628 T) has been observed in the 0.2 wt% nano‐NiFe 2 O 4 ‐doped sample, which are much higher than the undoped sample (28.81 N and 0.2754 T). T c measurement indicates that, a decreased onset T c of about 87.5 K and a broadened transition width of about 5 K are observed in the NiFe 2 O 4 ‐doped sample, indicating appearance of weak superconducting regions in superconducting matrix caused by Ni and Fe substitutions in Y‐123 crystal lattice. This study supplies a practical approach to increase the YBCO bulk performance significantly.