DC Magnetization Relaxation and the AC Susceptibility of YBCO Films with Strong Pinning

Abstract

AC susceptibility and DC magnetization relaxation measurements have been performed for YBa2Cu3O7 films containing BaZrO3 nanorods preferentially oriented along the c axis, with the external magnetic field perpendicular to the film surface. It was found that the effective vortex activation energy U e supplied by the standard analysis of the frequency dependent AC magnetic response remains very high even in the vicinity of the irreversibility line indicated by the DC relaxation. We show that the large U e values appearing in the AC signal are related to the pinning enhanced viscous drag and significant vortex velocities.