Manifestation of New Interference Effects in Superconductor/Ferromagnet Spin Valve

TL;DR

This paper reports the discovery of new interference effects in superconductor/ferromagnet spin valves, showing sign-changing oscillations in the superconducting transition temperature based on Fe2-layer thickness.

Contribution

It introduces a novel interference mechanism of Cooper pair wave functions causing sign-changing spin valve effects in S/F multilayer systems.

Findings

Full direct spin valve effect observed for Fe2-layer thickness < 1 nm.

Full inverse spin valve effect observed for Fe2-layer thickness >= 1 nm.

Interference of Cooper pair wave functions explains the oscillating behavior.

Abstract

Superconductor/ferromagnet (S/F) spin valve effect theories based on the S/F proximity phenomenon assume that the superconducting transition temperature Tc of F1/F2/S or F1/S/F2 trilayers for parallel magnetizations of the F1- and F2-layers (TcP) are smaller than for the antiparallel orientations (TcAP). Here, we report for CoOx/Fe1/Cu/Fe2/In multilayered systems with varying Fe2-layer thickness the sign-changing oscillating behavior of the spin valve effect \Delta Tc=TcAP-TcP. Our measurements revealed the full direct spin valve effect with TcAP>TcP for Fe2-layer thickness dFe2<1 nm and the full inverse (TcAP<TcAP) spin valve effect for dFe2>=1 nm. Interference of Cooper pair wave functions reflected from both surfaces of the Fe2-layer appear as the most probable reason for the observed behavior of \Delta Tc.