HOMOGENEITY MEASUREMENTS OF TRANSITION-TEMPERATURE AND CRITICAL-CURRENT DENSITY OF LARGE-AREA HTSC THIN-FILMS

An apparatus for measuring the homogeneity of the transition temperatu re (Tc) and the critical current density (Jc) of large area HTSC thin films has been developed. Two step motors are used to control the move ment of the scanning probe on a polar plane. There are two techniques included. The first is an ac inductive method which provides a nondest ructive measurement for determining Tc. Based on the Bean model, the s econd technique, for detecting the uniformity of Jc, uses the surface magnetic field distribution of the material to derive the Jc profile. Measurements were carried out on a 30mm diameter YBCO sample. A Tc map and surface distribution of the trapped field after field cooling whi ch responds to the Jc profile were obtained.