  Bulk melt-processed Y-Ba-Cu-O (YBCO) has significant potential for a variety
of high field permanent magnet-like applications, such as the rotor of a
brushless motor. When used in rotating devices of this kind, however, the YBCO
can be subjected to both transient and alternating magnetic fields that are not
parallel to the direction of magnetization and which have a detrimental effect
on the trapped field. These effects may lead to a long-term decay of the
magnetization of the bulk sample. In the present work, we analyze both
experimentally and numerically the remagnetization process of a melt-processed
YBCO single domain that has been partially demagnetized by a magnetic field
applied orthogonal to the initial direction of trapped flux. Magnetic torque
measurements are used as a tool to probe changes in the remanent magnetization
during various sequences of applied field. The application of a small magnetic
field between the transverse cycles parallel to the direction of original
magnetization results in partial remagnetization of the sample. Rotating the
applied field, however, is found to be much more efficient at remagnetizing the
bulk material than applying a magnetizing field pulse of the same amplitude.
The principal features of the experimental data can be reproduced qualitatively
using a two-dimensional finite-element numerical model based on an E-J power
law. Finally, the remagnetization process is shown to result from the complex
modification of current distribution within the cross-section of the bulk
sample.
