Comparative study of the vortex motion between in-fan and across-fan in YBa 2Cu 3O 7 single crystals with crossed columnar defects

Abstract

We have studied vortex motions along the across-fan and in-fan directions in YBa 2Cu 3O 7 single crystals with crossed columnar defects using micro-Hall probe array. We find anisotropic critical current density, J c, depending on the relative orientation of the vortex motion with respect to the defect configuration. J c was higher for the across-fan motion. On the other hand, the normalized relaxation rate, S, and the activation energy, U, did not show a clear anisotropy except at 30 K. The lack of obvious directional dependence in S and U compared to J c implies that the observed J c anisotropy is mainly due to the anisotropy in the flux bundle volume. In addition, during the flux entry below the full penetration we find the largest relaxation takes place at the advancing flux front.