Magnetic Relaxation in High-Tc Oxide Superconductors

Abstract
Magnetic relaxation was measured at 77 K for Bi-Sr-Ca-Cu-O, Tl-Ba-Ca-Cu-O and Y-Ba-Cu-O polycrystalline oxides in order to investigate thermally activated flux creep. The magnetic relaxation for Bi- and Tl-based bulk samples was larger than that for the Y-based samples. The magnetic relaxation for Bi-based samples was greatly decreased by powdering, which indicates that the large relaxation of the bulk samples is not an intrinsic property but is due to large flux creep at grain boundaries. The activation energy related to the flux-pinning was 0.13 and 0.19 eV for Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O compounds, respectively.