Using magnetic coupling in bilayers of superconducting YBCO and soft-magnetic CoFeB to map supercurrent flow

Abstract

Bilayers of high-temperature superconducting YBa2Cu3O7−δ and amorphous soft-magnetic CoFeB have been prepared by pulsed-laser deposition and subsequent ion beam sputtering. In such structures magnetic coupling phenomena are found between the superconducting component and the ferromagnetic component. First, a significant increase of the critical current in the superconductor at temperatures close to Tc is found which is attributed to magnetic flux line pinning. Second, magnetic coupling across the interface allows a transfer of the current pattern of the superconductor into the ferromagnet via magnetic stray fields. This creates a map of the current flow of the superconductor inside the ferromagnet which is persistent when heating the bilayer up to room temperature. If it can be realized that the ferromagnet does not harm the superconductor too much, this could offer an easy (and novel) way of characterizing the current transport in superconductors.