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

## TL;DR

This paper demonstrates that Nb/Co/Py/Nb multilayers exhibit a reversible increase in superconducting critical temperature when a non-collinear magnetic structure is present, enabling magnetic field control of superconducting properties.

## Contribution

It introduces a field-tunable non-collinear magnetic structure in Nb/Co/Py/Nb multilayers that enhances Tc and allows control over pair conversion and Josephson currents.

## Key findings

- Reversible 400 mK increase in Tc with non-collinear structure
- Magnetic field tunability of superconducting properties
- Potential for magnetic field controlled Josephson junctions

## Abstract

Over the last decade it has been shown that magnetic non-collinearity at a 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 bi-layer structure can function as a field tunable non-collinear magnetic structure which may offer magnetic-field tuneability 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 Tc with and without a non-collinear magnetic structure between Co and Py. The sensitivity of Tc 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.