High trapped fields were found in zinc-doped, bulk melt-textured YBa2Cu3O7−x (YBCO) material showing a pronounced peak effect in the field dependence of the critical current density. Trapped fields up to 1.1 T were found at 77 K at the surface of a YBCO disk (diameter 26 mm, height 12 mm). Very high trapped fields up to 14.35 T were achieved at 22.5 K for a YBCO disk pair (diameter 26 mm, height 24 mm) by the addition of silver and using a bandage made of stainless steel. The pinning forces and trapped fields obtained in bulk YBCO material are compared with results reported for melt-processed NdBa2Cu3O7−x and SmBa2Cu3O7−x.

Improved trapped fields are reported for bulk melt-textured YBa2Cu3O 7−δ (YBCO) material in the temperature range between 20 K and 50 K. Trapped fields up to 12.2 T were obtained at 22 K on the surface of single YBCO disks (with Ag and Zn additions). In YBCO mini-magnets, maximum trapped fields of 16 T (at 24 K) and of 11.2 T (at 47 K) were achieved using (Zn + Ag) and Zn additions, respectively. In all cases, the YBCO disks were encapsulated in steel tubes in order to reinforce the material against the large tensile stress acting during the magnetizing process and to avoid cracking. We observed cracking not only during the magnetizing process, but also as a consequence of flux jumps due to thermomagnetic instabilities in the temperature range betweeen 20 K and 30 K. 7460Ge, 7462Bf, 7480BjBulk type II superconductors can trap high magnetic fields that are generated by superconducting persistent currents circulating macroscopically within the superconductor. The main features of the resulting field distribution are a maximum trapped field B 0 in the center of the superconducting domain and a field gradient towards the sample edge which is determined by the critical current density j c of the supercurrents. Therefore, high trapped fields B 0 in bulk superconductors require a high critical current density and a large size of the current loops. Large single-domain bulk YBa 2 Cu 3 O 7−δ based (YBCO) samples can be produced by melt texture processing, especially by using SmBa 2 Cu 3 O 7−δ (Sm-123) as a seed crystal.[1] The pinning effect in melt textured samples can be improved by irradiation methods [2,3] and alternatively, by zinc-doping. [4,5] Cracking of the samples was found to limit the trapped field of bulk YBCO at temperatures below 77 K which can be explained by tensile stresses that occur during the magnetization process due to the stored flux density gradient and may exceed the tensile strength of the material.[6] The mechanical properties of bulk YBCO and its tensile strength can be improved considerably by the addition of Ag. [7,8] Another possibility to avoid cracking during magnetizing is to encapsulate the bulk YBCO disks in steel tubes. [9] A steel tube leads to stress compensation by generating a compressive stress on YBCO after cooling from 300 K to the measuring temperature which is due to the higher thermal expansion coefficient of steel compared to that of YBCO in the a, b-plane. Maximum trapped fields B 0 of 11.5 T at 17 K and of 14.4 T at 22 K were reported for single YBCO disks and mini-magnets consisting of two single YBCO disks, respectively. [9] In both cases, Ag was added to the YBCO disks which were placed into austenite Cr-Ni steel tubes. Previous attempts to combine the two beneficial effects of Ag and Zn additions failed due to the solubility of Zn in Ag in oxygen atmosphere. High trapped fields have also been reported for bulk Sm-123 with additions of Ag. At the surface of Sm-123 disks, trapped fields of 2.1 T at 77 K and of 8 T at 40 K have been observed. [10] In the present paper, t...

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