Magnetization and critical current of finite superconductingYBa2Cu3O7rings

Abstract

The irreversible magnetization of finite melt-textured $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ rings in perpendicular applied fields, affected by demagnetizing effects, is presented. The influence of the ring aspect ratio on the initial flux penetration and magnetization loops is studied by Hall probe and SQUID magnetometry. A general methodology based on the critical state model is developed in order to determine the critical current density from the field of full penetration ${H}_{\mathrm{pen}}$ in finite rings. We demonstrate that due to the field dependence of the critical current, the full penetration field ${H}_{\mathrm{pen}}$ of a finite ring does not coincide in general with the ``kink'' appearing in the initial magnetization curve. However, under certain conditions [very thin/narrow rings, or weak ${J}_{c}(H)$ dependence] the two fields collapse, and the critical current density can then be easily determined from the ``kink'' in the initial magnetization curve. In this latter situation, we develop an expression to determine the critical current density from the magnetic field measured at the center of the ring by Hall probe magnetometry.