ANGULAR REVERSIBILITY AND IRREVERSIBILITY OF CRITICAL CURRENT IN POLYCRYSTALLINE YBA2CU3O7 WIRES

A detailed discussion of the influence of the rotation of Ag-YBa2CU3O7 wires about their longitudinal axis in an external magnetic field on the critical current value is presented. In particular the angular dependence of the local field, defined as a superposition of the trapped flux and the externally induced magnetic flux, in superconducting rings (loops) and superconducting grains on the transport critical current paths has been computer-modelled and analysed. Irreversibility of the I(c)(omega, B) function is observed for the rotation angle range from O to pi. This behaviour is induced by the irreversibility of the screening current paths in the wire which occurs as a consequence of the readjustment of the local magnetic flux affecting the critical current of weak junctions. The shape of the I(c)(omega, B) function for further rotation of the wire matches the stable cyclic variation and is not irreversible.