Accounting the size distribution of HTS granules for the critical current density from magnetic measurements

The determination of the critical current density from magnetic hysteresis loops is widely used to characterize and compare superconducting samples. For tapes and single crystals, magnetic hysteresis loops depend on both the critical current density and the sample size, which determine the scale of supercurrent circulation. However, in polycrystalline hightemperature superconductors prepared by solid-phase synthesis or the sol-gel method, the magnetization is determined by the circulation of supercurrents in the granules. The effect of the granule size distribution on the effective scale of current circulation is discussed in the paper. The log-normal distribution and the Weibull distribution are considered. The effective size for estimating the intragranular critical current density can be significantly larger than the average granule size.