Signatures of superconducting exchange coupling revealed through magnetic switching experiments

Superconductor-mediated exchange between two ferromagnetic insulators is predicted to result in an antiferromagnetic coupling between the two ferromagnetic insulating layers, thus locking the magnetization vectors in an antiparallel alignment. Such a scenario intuitively assumes the ferromagnetic magnetizations as macrospins lacking a magnetic microstructure. In order to test the validity of this assumption and to test the stability of the antiparallel alignment, we perform various switching experiments that attempt to either maintain or deliberately induce a domain structure in the ferromagnetic layers. Irrespective of the switching experiment we perform, we find a distinctive preference for the antiparallel alignment with increasing strength of superconductivity. We also achieve robust nonvolatile bistability of electronic states due to a pronounced macrospin behavior induced by superconducting exchange coupling.