A IMPROVED APPROACH TO EVALUATE THE PINNING EFFECT OF VORTICES

The method to evaluate the pinning effect of the quantized vortices of magnetic flux is studied by measuring the magnetic relaxation in supe rconductivity using a SQUID-susceptometer. The experiments were carrie d out on typical type II superconductor Nb thin films. The amounts of grain boundaries that work as major pinning centers of the vortices ar e controlled by heat treatment. The time dependence of the magnetic mo ment shows that the driving force of on the flux lines is the deviatio n between initial magnetization and thermal equilibrium point of magne tization. In this approach the pinning potential Up can be estimated.