On the extended elliptic critical-state model for hard superconductors

Abstract

The magnetic behavior of an irreversible type-II superconducting slab under the action of in-plane crossed fields is investigated within both the original elliptic critical-state model and the extended one, which was recently proposed by Clem. In particular, we study the suppression of the remanent magnetization of a PbBi specimen by a sweeping external transverse magnetic field. It is found that both elliptic critical-state models reproduce the main features of available experimental magnetization curves. We also show that the average magnetizations, corresponding to diamagnetic and paramagnetic initial states at a static bias field H z , are asymmetrically reduced by the action of an oscillating transverse field H y . If the amplitude of the oscillations of H y is as large as the first penetration field H P , the resulting state becomes paramagnetic after various cycles of H y . Such a kind of paramagnetism is attributed to the anisotropy, induced by flux-line cutting effects, in the critical current density. In PbBi samples, paramagnetism is expected to be manifest in a wide range of values of the static bias field H z .

Bianisotropic-critical-state model to study flux cutting in type-II superconductors at parallel geometry

“…These results show that paramagnetism occurs in a sample with intrinsic anisotropy when the applied fields are comparable to the penetration field [20,21]. Both graphics present the main characteristics obtained with the ECSM and EECSM [20,21,28]. Here, the particular case was presented when both magnetic fields are of the same order of m H pz 0 .…”

“…Theoretical calculations were compared with the remanent magnetization á ñ M z of a superconducting lead-bismuth (PbBi) disk subjected, first to a single pulse of H z , and later to an oscillating field H y . Even though the theoretical curves á ñ M z versus H y obtained with both models were similar, the evolution of the B z profiles, given by the EECSM, contradicts the case when the H y and H z magnitudes are similar to the penetration field H p [28].…”

Flux cutting in high-Tcsuperconductors

“…In crossing or rotating fields there can be a few spatial zones in the sample where vortices are stable, move under transverse currents, experience cutting (and thus rotation), or both move and cut [13]. This scenario appears in all current GCSMs with some variation in details (see refs in [17,42,16,18]). …”

Theory of Flux Cutting for Type-II Superconducting Plates at Critical State

“…First, the disk is magnetized with a single pulse of a H z field, and subsequently it is subjected to an oscillating magnetic field H y . Even though the theoretical curves M z vs H y obtained with each model are very similar, the profile evolution of B z obtained by using the extended ECSM contradicts the cases when the magnitude of fields H y and H z are comparable to H p [5].…”