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 J(C). The invasion of magnetic flux above H(Cl) 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 Nb0.5Ti0.5.