Superconducting permanent magnets

Bulk melt textured YBa2Cu3O7-δ related material (YBCO) with single-domain grains up to 35 mm in diameter was developed as material for superconducting permanent magnets. The maximum trapped field of superconducting permanent magnets is determined by the critical current density of the supercurrents and the size of the current loops. Trapped fields up to 1.1 T were found at 77 K at the surface of zinc-doped YBCO disks. This newly processed material shows a pronounced peak effect in the field dependence of the critical current density suggesting strong pinning defects in the material. The trapped field in YBCO at temperatures below 77 K, which increases due to higher critical current, is limited by the tensile strength of the material that is exposed to considerable Lorentz forces. Very high trapped fields up to 14.35 T were achieved at 22.5 K in the gap between two YBCO disks (26 mm in diameter) by the addition of silver and by using a bandage made of stailess steel. (orig.)