Magnetic field tunable superconducting transition in Nb/Co/Py/Nb exchange spring multilayers

Abstract

Over the last decade, it has been shown that magnetic non-collinearity at an s-wave superconductor/ferromagnet interface is a key ingredient for spin-singlet to spin-triplet pair conversion. This has been verified in several synthetic non-collinear magnetic structures. A magnetically soft and hard ferromagnetic layer combination in a bilayer structure can function as a field tunable non-collinear magnetic structure, which may offer magnetic field tunability of singlet-to-triplet pair conversion. From magnetization measurements of Nb/Co/Py/Nb multilayers, we demonstrate a reversible enhancement of the superconducting critical temperature of 400 mK by measuring T c with and without a non-collinear magnetic structure between Co and Py. The sensitivity of T c in these structures offers the potential for realizing magnetic field tunable Josephson junctions in which pair conversion and Josephson critical currents are controllable using modest magnetic fields.