Robustness of the $0 -\pi $ transition against compositional and structural ageing in S/F/S heterostructures

TL;DR

This study investigates how aging affects the $0- ext{-}\pi$ transition in Nb/PdNi/Nb heterostructures, revealing that structural and compositional changes influence the transition temperature and interface properties.

Contribution

It demonstrates that the $0- ext{-}\pi$ transition remains observable despite interface imperfections caused by aging, highlighting the transition's robustness.

Findings

Aging shifts the $0- ext{-}\pi$ transition temperature.

Structural and compositional changes occur with aging.

The $0- ext{-}\pi$ transition persists despite interface imperfections.

Abstract

We have studied the temperature induced $0 -\pi $ thermodynamic transition in Nb/PdNi/Nb Superconductor/Ferromagnetic/Superconductor (SFS) heterostructures by microwave measurements of the superfluid density. We have observed a shift in the transition temperature with the ageing of the heterostructures, suggesting that structural and/or chemical changes took place. Motivated by the electrodynamics findings, we have extensively studied the local structural properties of the samples by means of X-ray Absorption Spectroscopy (XAS) technique, and the compositional profile by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). We found that the samples have indeed changed their properties, in particular for what concerns the interfaces and the composition of the ferromagnetic alloy layer. The structural and compositional data are consistent with the shift of the $0-\pi$ transition toward the behaviour of heterostructures with different F layers. An important emerging indication to the physics of SFS is the weak relevance of the ideality of the interfaces: even in aged samples, with less-than-ideal interfaces, the temperature-induced $0-\pi$ transition is still detectable albeit at a different critical F thickness.