An Explanation for Observed Flux Creep in Opposite Direction to Lorentz Force in Partially Magnetized Bulk Superconductors

Abstract

Sawh et al. recently reported experimental results that showed, in the case of a partially magnetized bulk superconductor, magnetized using zero-field-cooling, that flux creep resulted in a reduced field measured at the center of the top surface of the bulk. The authors reported that this may suggest magnetic flux vortices, in this case, move against the Lorentz force, contravening commonly-accepted theory. In this paper, we report the results of numerical simulations explaining the observed measurements, and show that the vortices do indeed move with the Lorentz force, but geometric effects from the finite geometry of the bulk and the form of the resulting induced supercurrent flowing within the bulk play a key role in this observed phenomenon. As a result, the relaxation of the magnetic flux can result in a measured magnetic field above the bulk superconductor that could be perceived as magnetic flux moving against the Lorentz force, when applying a simple Bean model (infinite slab) analysis to the problem.