The studies of bilayers and trilayers of ferromagnets and superconductors in a spin valve core structure

Abstract

Superconductor (S) critical temperature oscillations and reentrant superconductivity with increasing thickness of ferromagnetic (F) layer in F/S nanolayered structures are based on interference effects of the superconducting pairing wave function. The Fulde-Ferrell Larkin-Ovchinnikov (FFLO) like state establishing in these geometries is the origin of the phenomenon. Up to now it has been extensively investigated on thin film S/F bilayers with first superconducting layer (S-layer is grown on the substrate). Recently, we have also observed the oscillating phenomena in F/S bilayers where Nb as the S-metal now is grown on the top of the Cu41Ni59 as F-material. Junction of both kinds of bilayers yields an F/S/F trilayer, being the core structure of a superconducting spin valve. For all mentioned cases, we observed deep oscillations of superconducting critical temperature, Tc, and reentrant superconductivity, which are the necessary condition to obtain a large spin switching effect, i.e., a large shift in Tc, if the relative orientation of the magnetizations of the F-layers is changed from parallel to antiparallel.