Magnetic confinement of the superconducting condensate in superconductor/ferromagnet hybrid composites

TL;DR

This paper investigates how inhomogeneous magnetic fields from ferromagnetic structures influence superconductivity in thin Al films, demonstrating tunable confinement effects that alter the critical temperature behavior.

Contribution

It reveals how ferromagnetic stray fields can reversibly control superconducting condensate confinement and modify the Tc(H) phase boundary in superconductor/ferromagnet hybrids.

Findings

Stray fields confine the superconducting condensate.

Magnetic state switching tunes Tc(H) dependence.

Reentrant superconducting phase boundary observed.

Abstract

The influence of an inhomogeneous magnetic field on the magnetoresistance of thin Al films, used in different superconductor/ferromagnet hybrids, has been investigated. Two contrasting magnetic textures with out-of-plane magnetization are explored, namely (i) a plain film in a multidomain state and (ii) an array of micro-sized dots. The stray fields of the ferromagnetic structures confine the superconducting condensate and, accordingly, modify the condition for the nucleation of superconductivity. By switching between different magnetic states of the ferromagnet, this confinement can be tuned at will, hereby reversibly changing the dependence of the critical temperature Tc on an external magnetic field H. In particular, the continuous evolution from a conventional linear Tc(H) dependence with a single maximum to a reentrant superconducting phase boundary with multiple Tc peaks has been demonstrated.