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

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 t he 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 respectiv e contributions to total hysteresis. The method is tested with Y-133 and ap plied to Hg(15%Re)-1223. The surface contribution to irreversibility in the Hg-based HTSC significantly exceeds that of Y-123. It approximately follow s the reciprocal field dependence, mu(0)Delta M = B-p(2)/B-0, of the Clem m odel. Surface barriers provide the major contribution to irreversibility in Hg-based HTSC powder. The method brings a new, self-consistent evidence fo r strong surface barriers being a characteristic property of HE-based HTSC. (C) 1999 Elsevier Science B.V. All rights reserved.