Direct observation of magnetic flux behavior in high- Tc YBa 2Cu 30 x superconductors using the magneto-optical effect of iron garnet films

Abstract

The magnetic flux behavior in YBa 2Cu 3O x , specimens at various applied fields was observed at 10 and 77 K using the Faraday effect of iron garnet films with perpendicular magnetization and stripe magnetic domains. Magneto-optical observation of the domain structure in the iron garnet film placed on the sample revealed the magnetic flux distribution. The magnetic flux gradients in melt processed crystals at both 10 and 77 K are in good agreement with that predicted by the critical state model. On the other hand, in a sintered sample the flux penetrated through the superconducting weak-link regions and no flux gradient was observed at 77 K. However, the critical state was weakly held for the macroscopic sample volume at 10 K due to the increase of intergrain critical currents.