Critical-current density from magnetization loops of finite high-Tc superconductors

We analyze the effects of demagnetizing fields in the magnetization hysteresis loops of type-II superconductors, by a model that allows the calculation of current and field profiles in finite cylindrically symmetric superconductors in the critical state. We show how the maximum in the magnetization curve gradually shifts from negative applied field values to the central position with decreasing sample thickness. From the analysis of the calculated field profiles, we demonstrate that one can obtain the intrinsic field-dependent critical-current density of the superconductor with great accuracy by measuring the magnetic response of superconductors with large aspect ratio with the applied field parallel to the shortest dimension.