Measurement of the transition temperature distribution and magneticfield profile of large superconducting films

A novel apparatus has been developed to measure the transition temperature (T_c) distribution and magnetic field profile of large superconducting films. Two techniques were used. The first one is an ac inductive method which provides a contactless measurement of T_c. The second technique employs a Hall device to measure magnetic field. Driven by two step motors, the measuring probe, either a two-coaxial-winding coil or a Hall sensor, can move over the sample on a polar plane. As the probe scans the sample step by step, various points on the sample are measured one by one. Experiments were carried out on a 30 mm diameter YBa₂Cu₃O_7-δ thin-film. The T_c distribution and the surface profile of trapped magnetic field were obtained