High magnetic fields in superconducting permanent magnets

We report on the temperature dependence of the maximum trapped field B-o(T) in the high-T-c superconductor YBa2Cu3O7-x (YBCO). Trapped fields of bulk melt-textured YBCO samples are limited by their pinning behaviour and mechanical properties. The mechanical properties of bulk YBCO samples were improved by the addition of silver. Furthermore, the YBCO disks were encapsulated in steel tubes in order to reinforce the material against the large tensile stress acting during the magnetizing process. High trapped fields up to 13.3 T were measured at 33 K on the surface of a single YBCO disk containing Ag additions and reinforced with steel tubes. The flux pinning properties of this YBCO disk were improved by neutron irradiation and Zn doping resulting in a significant shift of the trapped field curve B-o(T) to higher temperatures. In YBCO mini-magnets, consisting of two YBCO disks, maximum trapped fields up to 16.0 T were achieved at 24 K by a combination of Zn-doping and Ag addition. The improved reinforcement, which was used in this case, was found to withstand the maximum trapped field of 16 T without cracking.