INVESTIGATION OF THE MIXED STATE OF YBA2CU3O7-DELTA SUPERCONDUCTORS

The magneto-optical Faraday effect has been used to observe the penetration of magnetic flux into sintered YBa2 Cu3 O 7-δ. In addition, measurements of the magnetic polarization are performed with a SQUID magnetometer. The magneto-optical Faraday effect shows an inhomogeneous penetration of the magnetic flux into the sample. In a first step the flux penetrates into the intergranular regions and in a second step into single grains separately. A spatial gradient of the flux density within each grain is built up, indicating pinning forces. In the remanent state in each grain trapped flux is observed. The measured magnetization curves show good agreement with the magneto-optical investigations of the flux penetration.