Effect of Columnar Defects on Magnetization of Mesoscopic Superconductors

In this work we investigated magnetization and vortex configurations in mesoscopic superconducting samples in the presence of square columnar defects (CDs). We solved numerically the nonlinear TDGL equations for different samples to study magnetization as a function of the applied magnetic field. In calculations, we focused mainly on four samples with different numbers of CDs which have the same total surface area. In this way, the total superconducting area remained the same with increasing the number of CDs for a fixed sample size. We found that the superconducting regions still exist inside the sample at high applied magnetic fields with increasing the number of CDs but irreversible effects became increasingly prominent, when the field is returned to zero. The results are discussed in frame of surface and pinning effects in mesoscopic systems.