A method to separate bulk and surface hysteresis contributions in HTSC powder by particle size classification and its application to Hg(Re)-1223

摘要

A particle size classification method is developed to separate bulk pinning from pinning at surface barriers in high-T_c superconducting (HTSC) powder material. The powder is fractionized into particle-size classes by passing it through sieving cascades. An analysis of magnetic hysteresis loops in the different particle size classes is performed on the basis of a Bean-like critical state model including surface-barrier induced irreversibility of the magnetization. This leads to a quantitative separation of the respective contributions to total hysteresis. The method is tested with Y-123 and applied to Hg(15%Re)-1223. The surface contribution to irreversibility in the Hg-based HTSC significantly exceeds that of Y-123. It approximately follows the reciprocal field dependence, #mu#_0 triangle open M = B_p~2/B_0, of the Clem model. Surface barriers provide the major contribution to irreversibility in Hg-based HTSC powder. The method brings a new, self-consistent evidence for strong surface barriers being a characteristic property of Hg-based HTSC.