Inverse magnetic hysteresis of the Josephson supercurrent: study of the magnetic properties of thin niobium/permalloy (Fe_{20}Ni_{80}) interfaces

TL;DR

This study investigates the magnetic properties and inverse magnetic hysteresis of Nb/permalloy interfaces in superconductor/ferromagnet heterostructures, revealing a shift in critical current oscillations relevant for memory and spintronic applications.

Contribution

It provides a comprehensive characterization method for S/F heterostructures and demonstrates inverse magnetic hysteresis effects consistent with recent theoretical predictions.

Findings

Presence of a magnetic stray field in F layers.

Correlation between magnetic measurements and Josephson junction behavior.

Observation of inverse Fraunhofer oscillation shift.

Abstract

We propose a picture for the magnetic properties of superconductor/ferromagnet (S/F) heterostructures based on Nb and permalloy (Py: Fe_{20}Ni_{80}). By measuring the magnetic moment as a function of the temperature in S/F/S trilayers for different thicknesses of the middle F layer, we give evidence of the presence of a magnetic stray field of the F layer. For values of F-layer thickness below a threshold, we establish a correlation between the magnetic measurements of the S/F/S trilayers and the anomalous magnetic dependence of the critical current in S/insulator/thin superconducting film/F/S (SIsFS) Josephson junctions (JJs). These complementary investigations provide a self-consistent method to fully characterize S/F heterostructures and possibly demonstrate effects arising from the mutual interactions between ferromagnetism and superconductivity. A shift in the Fraunhofer critical current oscillations has been observed in the opposite direction to the one commonly observed in JJs with F barriers, as it has been recently predicted by inverse and electromagnetic proximity theories. This inverse memory effect is relevant for the design of these heterostructures as memory cells and spintronic devices.