Bulk melt-processed (RE)BCO superconductors subjected to AC fields in “parallel” and “crossed” direction, experiment and modelling

When bulk melt-processed (RE)BCO samples are used as permanent magnets in various engineering applications (e.g. rotating machines, magnetic bearings), they may experience transient or periodic variations of the applied magnetic field. In such a situation, the remnant magnetization of the sample is found to decrease in running operation, which is particularly inconvenient for the long-term reliability of the system. There are several possible causes for such a phenomenon. The first is the temperature increase resulting from the losses caused by the variable applied field, and may arise when the field is parallel to the main direction of the trapped flux. The second is caused by the component of the magnetic field perpendicular to the main direction of the trapped flux (“crossed field” configuration). In the present talk we review the relevant parameters which have a detrimental impact on the remnant magnetization in both cases. Modelling results are compared to experimental data obtained on bulk YBCO samples subjected to field oscillations of large amplitude.