Scanning Hall microprobe measurements of magnetization profiles in YBa2Cu3O7−y single crystals

Abstract

A scanning Hall microprobe technique has been developed to measure the magnetic field around superconductors, and to make precision measurements of the ‘‘critical state’’ profiles in single crystals of YBa₂Cu₃O_7−y. The field around a superconducting crystal has been calculated for the Meissner state and for the remanent state. This enables a quantitative analysis of the critical state profiles, and a novel method to determine J_C. The invasion of magnetic flux above H_C1 was examined and this provides direct evidence for the existence of a surface barrier to the entry of magnetic flux lines. The temperature dependence of J_C was also measured and compared with that of the low T_C material Nb_0.5Ti_0.5.