Irreversible Magnetization of Pin-Free Type II Superconductors

TL;DR

This paper develops a quantitative theory explaining the geometric irreversibility in the magnetization of pin-free type II superconductors caused by edge barriers, comparing theoretical loops with ideal ellipsoids.

Contribution

It introduces a new theoretical model for the hysteretic magnetization behavior in pin-free superconductors with specific geometries.

Findings

Magnetization loops differ from reversible curves in ideal ellipsoids.

Edge barriers cause geometric irreversibility in superconductors.

The theory matches experimental observations for disks and strips.

Abstract

The magnetization curve of a type II superconductor in general is hysteretic even when the vortices exhibit no volume or surface pinning. This geometric irreversibility, caused by an edge barrier for flux penetration, is absent only when the superconductor has precisely ellipsoidal shape or is a wedge with a sharp edge where the flux lines can penetrate. A quantitative theory of this irreversibility is presented for pin-free disks and strips with constant thickness. The resulting magnetization loops are compared with the reversible magnetization curves of ideal ellipsoids.