Origin of the Inverse Spin Switch Effect in Superconducting Spin Valves

TL;DR

This paper investigates the inverse spin switch effect in superconducting spin valves, revealing it originates from vortex flow caused by stray magnetic fields from domain walls, which coexists with the standard effect.

Contribution

It demonstrates the coexistence of standard and inverse spin switch effects and identifies vortex flow from stray fields as the cause of the inverse effect.

Findings

Inverse SSE coexists with standard SSE in NiFe/Nb/NiFe spin valves.

Inverse SSE is caused by vortex flow from stray magnetic fields.

Stray fields originate from magnetostatically coupled domain walls.

Abstract

The resistance of a ferromagnet/superconductor/ferromagnet (F/S/F) spin valve near its superconducting transition temperature, $T_c$, depends on the state of magnetization of the F layers. This phenomenon, known as spin switch effect (SSE), manifests itself as a resistance difference between parallel ($R_P$) and antiparallel ($R_{AP}$) configurations of the F layers. Both standard ($R_{P}>R_{AP}$) and inverse ($R_{P}<R_{AP}$) SSE have been observed in different superconducting spin valve systems, but the origin of the inverse SSE was not understood. Here we report observation of a coexistence of the standard and inverse SSE in Ni$_{81}$Fe$_{19}$/Nb/Ni$_{81}$Fe$_{19}$/Ir$_{25}$Mn$_{75}$ spin valves. Our measurements reveal that the inverse SSE arises from a dissipative flow of vortices induced by stray magnetic fields from magnetostatically coupled N\'eel domain wall pairs in the F layers.