Theoretical Model of Superconducting Spintronic SIsFS Devices

TL;DR

This paper presents a theoretical analysis of magnetic SIsFS Josephson junctions, exploring their operational modes, current characteristics, and magnetic switching behavior, with implications for cryogenic memory in SFQ circuits.

Contribution

It introduces a comprehensive theoretical model of SIsFS junctions, highlighting their large $I_C R_N$ product and magnetic switching capabilities, aligning well with experimental data.

Findings

Large $I_C R_N$ product in the $ au$ state.

Multiple operational modes of the junctions.

Good agreement with experimental measurements.

Abstract

Motivated by recent progress in development of cryogenic memory compatible with single flux quantum (SFQ) circuits we have performed a theoretical study of magnetic SIsFS Josephson junctions, where 'S' is a bulk superconductor, 's' is a thin superconducting film, 'F' is a metallic ferromagnet and 'I' is an insulator. We calculate the Josephson current as a function of s and F layers thickness, temperature and exchange energy of F film. We outline several modes of operation of these junctions and demonstrate their unique ability to have large product of a critical current $I_{C}$ and a normal-state resistance $R_{N}$ in the $\pi$ state, comparable to that in SIS tunnel junctions commonly used in SFQ circuits. We develop a model describing switching of the Josephson critical current in these devices by external magnetic field. The results are in good agreement with the experimental data for Nb-Al/AlO${_x}$-Nb-Pd$_{0.99}$Fe$_{0.01}$-Nb junctions.