Hierarchy of critical temperatures in four-layered ferromagnet/superconductor nanostructures and control devices

摘要

The four-layered F/S/F$'$/S$'$ nanostructure consisting of rather dirtysuperconducting (S) and ferromagnetic (F) metals is studied within the theoryof the proximity effect taking detailed account of the boundary conditions. TheF/S structures with four F and S layers are shown to have considerably richerphysics than the F/S/F trilayer (due to the interplay between the 0 and $\pi$phase superconductivity and the 0 and $\pi$ phase magnetism) and even the F/Ssuperlattices. The extra $\pi $ phase superconducting states obtained for thefour-layered F/S/F$^{\prime }$/S$^{\prime }$ system are found to be differentfrom the known "superlattice" states. The dependence of the criticaltemperatures versus the F layers thicknesses is investigated. An optimal set ofparameters is determined, for which the difference between the criticaltemperatures for different states becomes significant, and the correspondingphase diagrams are plotted. It is proven that this system can have differentcritical temperatures for different S and S$'$ layers. A conceptual scheme of acontrol device with superconducting and magnetic recording channels that can becontrolled separately using a weak external magnetic field is proposed on thebasis of the F/S/F$'$/S$'$ nanostructure. The devices with four, five, six, andseven different states are explored.