Direct Observation of Flux Behavior in High-T_c Oxide Superconductors Using The Faraday Effect of Iron Garnet Films

A new direct observation method for the dynamical magnetic flux behavior in superconductors was developed by using the Faraday effect of an iron garnet film with perpendicular magnetization and stripe domains. The domain structure observed optically in the iron garnet film in contact with an YBa₂Cu₃O_x sample reveals the magnetic field distribution of the latter. It was found that the flux gradient was nonuniform due to the inhomogeneous distribution of fine Y₂BaCuO₅ inclusions, and the region with the largest pinning force was located in the sample used.