PROXIMITY AND COUPLING EFFECTS IN SUPERCONDUCTOR FERROMAGNET MULTILAYERS/

New features in superconductor/fenomagnet multilayers have been observ ed. A nonmonotonic dependence of the superconducting T-c on the ferrom agnetic layer thickness, due to the coupling across a thin magnetic la yer, has been observed in both Nb/Gd multilayers and trilayers. The re sults are consistent with those of the predicted pi-phase coupling. Ef fects on superconductivity due to insulating ferromagnetic layers have been observed in NbN/GdN multilayers, where the main pair-breaking ef fect is that of the ferromagnetic walls. The insulating ferromagnetic layers also give rise to very large superconducting critical fields. ( C) 1997 American Institute of Physics.