Shape effects on the magnetization of superconducting lead at 4.2K

Magnetization measurements performed on lead samples at 4.2K show how the position of maximum magnetization of the hysteretic magnetic behaviour are related to shape effects. It is possible to obtain reversible or irreversible magnetization curves by modifying the sample shape. These curves are in agreement with the two stage flux penetration process into cylinders and discs already studied by other authors and recently discussed elsewhere. From this discussion, a simple model using conformal mapping leads to a formula giving the applied field at which the second stage occurs as a function of thickness over diameter ratio. The results are in good agreement with experimental values for discs and with a computation performed by other authors. Magnetization curves of altered spheres present interesting features which seem unknown in the literature and which may be roughly interpreted using the same ideas.