Boosting the superconducting spin valve effect in a metallic superconductor/ferromagnet heterostructure

TL;DR

This study shows that the surface smoothness of the superconducting layer in S/F heterostructures greatly enhances the superconducting spin valve effect, highlighting the importance of interface quality for device performance.

Contribution

It demonstrates that smoother superconducting layers significantly improve the superconducting spin valve effect in S/F heterostructures, emphasizing the role of morphology in device optimization.

Findings

Smoother S layers lead to a larger spin valve effect.

Interface quality affects the performance more than the suppression of critical temperature.

Homogenization of the Green function enhances the spin valve effect.

Abstract

Superconducting spin valves based on the superconductor/ferromagnet (S/F) proximity effect are considered to be a key element in the emerging field of superconducting spintronics. Here, we demonstrate the crucial role of the morphology of the superconducting layer in the operation of a multilayer S/F1/F2 spin valve. We study two types of superconducting spin valve heterostructures, with rough and with smooth superconducting layers, using transmission electron microscopy in combination with transport and magnetic characterization. We find that the quality of the S/F interface is not critical for the S/F proximity effect, as regards the suppression of the critical temperature of the S layer. However, it appears to be of paramount importance in the performance of the S/F1/F2 spin valve. As the morphology of the S layer changes from the form of overlapping islands to a smooth case, the magnitude of the conventional superconducting spin valve effect significantly increases. We attribute this dramatic effect to a homogenization of the Green function of the superconducting condensate over the S/F interface in the S/F1/F2 valve with a smooth surface of the S layer.