Flux relaxation phenomena in the presence of weak AC magnetic fields

Abstract

Relaxation of flux profile and magnetisation due to non-linear vortex diffusion in a superconducting slab settled in a parallel-to-the-surface DC and superimposed weak AC magnetic fields is studied for several kinds of the non-linear vortex diffusivity, corresponding to different possible shapes of the current–voltage characteristics of the superconductor. The evolution of the dynamic vortex response on applied weak AC field due to flux relaxation process is studied and relaxation characteristics of the AC magnetic susceptibility are calculated. The flux creep rate and magnetisation decay are shown to be enhanced significantly in the case of strongly non-linear regime of vortex diffusion if even rather weak AC magnetic field is applied. The possibility of `dynamical melting' of the vortex lattice occurring at rather high levels of the induced current density ( j> j c) is also demonstrated.