Superconducting levitation at 90 K - A base for construction of non-contact liquid oxygen pumps

We report on a new type of nanometre-scale pinning defect in melt-processed (Nd, Eu, Gd)Ba₂Cu₃O_y, 'NEC-123' with a Gd ₂BaCuO₅ (Gd-211) addition. A reasonable amount of the Gd-211 particles refined by a long-term ball milling to about 70-200 nm reduced their size during the melt-texturing process down to 20-50 nm. Chemical analyses revealed that these particles contained a significant amount of zirconium. These particles caused J_c enhancement by an order of magnitude not only at 77 K but also at 90 K. As a result, we could levitate a permanent magnet over the (Nd, Eu, Gd)Ba₂Cu₃Oy superconductor cooled by liquid oxygen. This is a path to non-contact pumps of liquid oxygen for different fields of practice.