Flux-trapping phenomena in sintered tubes of high-${\mathit{T}}_{\mathit{c}}$ superconductors

The remanent magnetic flux density trapped in the cavity and in the wall of sintered tubes of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O was measured as a function of ${\mathit{H}}_{\mathrm{cool}}$, the axial magnetic field present during field cooling and then removed, and of ${\mathit{H}}_{\mathrm{cycle}}$, the axial magnetic field impressed and removed after zero-field cooling. For both procedures the two specimens exhibit very different behavior. A simple critical-state model which takes into account the return field of the magnetized grains quantitatively reproduces all of our observations and the corresponding data reported by others.