Critical current and resistivity measurements in a ceramic superconductor

Abstract
The critical current and resistivity of the ceramic superconductor Y1Ba2Cu3O7- delta have been measured by a very simple yet sensitive contactless technique. A toroidal specimen formed the tertiary winding of a small ferrite transformer. Signals from the secondary indicate when the critical current is exceeded in the superconducting state and yield the resistivity in the normal state. The mean critical current density in one specimen was found to be 90 A cm-2 at 77 K rising to 400 A cm-2 at 4.2 K.