Geometrical effects in the intermediate state of type-I Pb superconductors

Abstract

The influence of geometry on the nature of the intermediate state in superconducting type-I lead is presented. Isothermal measurements of first magnetization curves and hysteretical cycles of several cylindrical samples show an irreversible region when the magnetic field, parallel to the axis of revolution, decreases from the normal state. Comparing data for samples with different aspect ratio –length divided by diameter- has proved the existence of a geometrical barrier due to the shape and the orientation of the sample that strongly determines the behaviour of the magnetic flux. Finally, an analysis of the thermal dependence of the critical field, the irreversible field and the remnant magnetization for each sample is given in order to reinforce the idea that geometrical barriers are the fundamental cause of irreversibility.