Critical Current Density Estimation of YBCO by Trapped Field Measurement Using a Hall Probe

Abstract

An estimation of an intragranular critical current density Jc for a large YBCO bulk sample prepared by the MPMG method was performed by a trapped field measurement using a Hall probe. A single-domained rectangular YBCO sample (10mm×10mm×lmm) was field-cooled in liquid nitrogen under the field of 4000G. After the applied field was turned off, the field distribution in the area of l0mm×10mm was mapped by scanning the Hall probe at the interval of 0.5mm. The trapped field distribution was compared with the distributions calculated by numerical analyses assuming square current loops inside the sample. First, assuming a field-independent Jc, the measured profile was in good agreement with the calculated profile except in the high field region near the center. Therefore, the intragranular Jc was estimated to be 2.6×104A/cm2 (77K, 0T). Second, using the Irie-Yamafuji model taking into account a field-dependent Jc, the measured profile was in better agreement with the calculated profile even in the high field region. The material parameters in the relationship of J c =αB-n were found to be α=1.4×104A/cm2 and n=0.20. Finally, it is found that a trapped field measurement using a Hall probe is applicable to a Jc estimation of a large superconductor without destroying the sample.