Imperfection of flux pinning classification based on the pinning center size

Abstract

Magnetic flux pinning classification based on the pinning center size is found to be imperfect because of the proximity effect of superconducting state. The application of this idea to the Dew-Hughes model shows that the eight flux pinning functions in it are linearly dependent, which implies that some of these pinning mechanisms are not the primal ones, but a combination of others. Based on the physical considerations, ‘core, normal, surface pinning’ and ‘core, normal, point pinning’ are abandoned. A pinning function that is related to the self-field critical current is induced. Then seven linearly independent pinning functions are picked out to represent the seven primal pinning mechanisms, respectively. The application of these seven functions to the experimental data shows that they contribute to a better general description of the complex mechanism of the pinning of the superconductors.