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

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 YBa2Cu3O7−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 JC. The invasion of magnetic flux above HC1 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 JC was also measured and compared with that of the low TC material Nb0.5Ti0.5.