Superconducting permanent magnets from bulk YBa2Cu3 O7-δ samples

The properties of bulk melt-textured YBa₂Cu₃O_7-δ disks have been investigated with respect for use as trapped field magnets. Large single-domain disks up to 35 mm in diameter and 12 mm in thickness were obtained by a melt-texturing process. The trapped field in the 1 mm gap between two single-domain disks was found to increase from 1.2 T at 77 K up to 9.0 T at 47 K which is the highest trapped field achieved in non-irradiated samples. The trapped field at lower temperatures is limited by the mechanical strength of the material for which a value of 25 MPa was estimated. We observed an exponential decrease of the trapped field with increasing temperature, which can be explained by flux creep in the framework of collective pinning. The activation energy for this process was determined by relaxation measurements