Slowing-down of the vortex motion in the flux creep process by counter forces exerted on the vortex ends

Abstract

The effect of the suppression of flux creep in a high-temperature superconductor by counter forces exerted on the vortex ends was studied. These forces, acting in the opposite direction to the process of vortex diffusion, arise when the magnetized sample is put into a nonuniform magnetic field. The source of the field should be placed near the surface of the superconductor where the flux line ends are located. The critical states in a disk sample placed near a ferromagnet or permanent magnets were calculated. The results of the calculations verify the bipolar current structure and, therefore, the existence of counter Lorentz forces in the near-surface region. It was shown that in addition to the Lorentz force it is necessary to take into account the magnetic force acting on the vortex ends in the external nonuniform magnetic field. Depending on the direction of this force, the magnetic relaxation slows down or accelerates.