Pinning centres in NEG-123 active at liquid oxygen temperature (90.2 K)

We present a new type of (Nd, Eu, Gd) Ba₂Cu₃O_y 'NEG-123' material for superconducting permanent magnets for use at liquid oxygen temperature (90.2 K). This material exhibits an exceptionally high flux pinning up to the close vicinity of T_c. The improvement of the flux pinning was achieved by externally added ball-milled secondary phase particles that partially transformed during the technological process to a new type of nanometre-scale Zr-rich particles. The critical current density improved by one order of magnitude at 77 and 90 K as compared to those of other RE-123 type materials. The exceptional trapped field at 90.2 K enabled a levitation experiment at liquid oxygen temperature, which proved that these materials can be used as superconducting permanent magnets at 90 K. We point out that this technology can be easily adapted for mass production.