Demagnetization of cubic Gd-Ba-Cu-O bulk superconductor by cross-fields: measurements and 3D modelling

TL;DR

This study investigates the demagnetization effects in cubic Gd-Ba-Cu-O bulk superconductors caused by cross-fields, using combined 3D numerical modelling and experimental validation to understand current paths and magnetic behavior.

Contribution

It presents the first combined experimental and 3D modelling analysis of crossed-field demagnetization in cubic superconductor shapes, revealing complex current path behaviors.

Findings

Modelling results align with experiments below 50% of initial field.

Current paths exhibit strong 3D characteristics and smooth current density transitions.

Force free effects like flux cutting are significant in the demagnetization process.

Abstract

Superconducting bulks, acting as high-field permanent magnets, are promising for many applications. An important effect in bulk permanent magnets is crossed-field demagnetization, which can reduce the magnetic field in superconductors due to relatively small transverse fields. Crossed-field demagnetization has not been studied in sample shapes such as rectangular prisms or cubes. This contribution presents a study based on both 3D numerical modelling and experiments. We study a cubic Gd-Ba-Cu-O bulk superconductor sample of size 6 mm magnetized by field cooling in an external field of around 1.3 T, which is later submitted to crossed-field magnetic fields of up to 164 mT. Modelling results agree with experiments, except at transverse fields 50\% or above of the initial trapped field. The current paths present a strong 3D nature. For instance, at the mid-plane perpendicular to the initial magnetizing field, the current density in this direction changes smoothly from the critical magnitude, ${J_c}$, at the lateral sides to zero at a certain penetration depth. This indicates a rotation of the current density with magnitude ${J_c}$, and hence force free effects like flux cutting are expected to play a significant role.