Irreversibility-line study in the polycrystallineBi2Sr2CaCu2O8superconductor

Measurements of irreversible magnetization in the superconducting state of the ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ compound have been made using a dc magnetometer. It was found that the irreversible magnetization is proportional to (T-${\mathit{T}}^{\mathrm{*}}$ ${)}^{\mathit{n}}$, where ${\mathit{T}}^{\mathrm{*}}$ is the field-dependent irreversibility temperature and the power n is of the order of 5. The irreversibility temperature obeys the relation 1-${\mathit{T}}^{\mathrm{*}}$/${\mathit{T}}_{\mathit{c}}$∝${\mathit{B}}^{2/3}$ at fields up to 0.6 T. At higher fields, ${\mathit{T}}^{\mathrm{*}}$ was found to vary more slowly with the field, which is in agreement with previously published results.