Geometrical locking of the irreversible magnetic moment to the normal of a thin-plate superconductor

Abstract

We solve the Bean critical-state model for the screening current distribution in an infinite superconducting slab in a tilted magnetic field H, and calculate from it the magnitude and direction of the induced magnetic moment m. As the tilt angle increases, m remains directed close to the plate normal n until H is almost perpendicular to n, then m rotates very rapidly. We consider several generalizations of the model: finite length, a more realistic current-voltage characteristic, and critical-current anisotropy, but find that they have only a minor quantitative effect on the results derived for the simplest case. Also, we prove that the closure currents always contribute half the moment. Vector magnetic moment measurements of YBa2Cu3Oy single crystals and an epitaxial film, and also on samples of conventional superconductors, confirm the model calculations. These geometrical effects are important for the analysis of the angular behavior of the critical currents and their anisotropy in HTS materials; also, they assist the observation of vortex locking to twin boundaries in HTS crystals, but tend to obscure vortex locking to CuO planes.

Source-reported materials — not catalogue approval

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