Superconducting Current Density Profiles Estimated from the Flux Density Distribution in YBa 2 Cu 3 O x Thin Films

The flux penetration in superconducting thin films has been observed by means of the magnetooptical Faraday effect in iron garnet films. Bi- and Ga-substituted YIG films were used for the observation of the flux density distribution for the disk-shaped YBa 2 Cu 3 O x films with a radius of 0.5 mm and a thickness of 1800 Å. Critical current density J c was estimated from the whole profile of the flux density distribution without using Bean's model. The estimated J c is about 6×10 6 A/cm 2 at 10 K, and this value is smaller than that estimated using Bean's model from the remanent magnetization at the same temperature.