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

TL;DR

This paper investigates how the distribution of grain sizes in high-temperature superconductors affects the measurement of critical current density from magnetic hysteresis data, emphasizing the importance of considering grain size distribution.

Contribution

It introduces a method to account for grain size distribution effects, showing that the effective size for current circulation exceeds the average grain size in polycrystalline HTS.

Findings

Effective current circulation size is larger than average grain size.

Log-normal and Weibull distributions are suitable models for grain sizes.

Grain size distribution significantly influences critical current density calculations.

Abstract

The determination of the critical current density from magnetic hysteresis loops is widely used to characterize and compare superconducting samples. Magnetic hysteresis loops for tapes and single crystals depend on both the critical current density and sample size. The latter sets the scale of supercurrent circulation. However, in polycrystalline high-temperature superconductors prepared by solid-phase synthesis or by sol-gel method, the magnetization is determined by the circulation of supercurrents in individual grains. The paper discusses the effect of the grain size distribution on the effective scale of current circulation. Log-normal and Weibull distributions are both considered as possible for grain sizes. The effective size for calculating the intragrain current density has been shown to be significantly larger than the average grain size.