Phase Controllable Josephson Junctions for Cryogenic Memory

TL;DR

This paper demonstrates controllable 0-π phase switching in Josephson junctions with ferromagnetic layers, advancing cryogenic memory technology by expanding the known parameters for phase control.

Contribution

It provides phase-sensitive measurements confirming controllable phase switching in junctions with specific ferromagnetic layer thicknesses using improved SQUID analysis.

Findings

Confirmed 0-π phase switching in junctions with 2.0 nm Ni fixed layers and 1.25 nm NiFe free layers.

Expanded the phase diagram of thicknesses allowing phase control.

Validated phase switching across multiple devices and SQUID designs.

Abstract

Josephson junctions containing ferromagnetic layers have generated interest for application in cryogenic memory. In a junction containing both a magnetically hard fixed layer and soft free layer with carefully chosen thicknesses, the ground-state phase difference of the junction can be controllably switched between 0 and {\pi} by changing the relative orientation of the two ferromagnetic layers from antiparallel to parallel. This phase switching has been observed in junctions using Ni fixed layers and NiFe free layers. We present phase-sensitive measurements of such junctions in low-inductance symmetric SQUID loops which simplify analysis relative to our previous work. We confirm controllable 0 - {\pi} switching in junctions with 2.0 nm Ni fixed layers and 1.25 nm NiFe free layers across multiple devices and using two SQUID designs, expanding the phase diagram of known thicknesses that permit phase control.