Ferromagnetic Josephson junctions for cryogenic memory

TL;DR

This paper explores phase control in ferromagnetic Josephson junctions for cryogenic memory, discussing device optimization and proposing a phase diagram for material configurations to enhance large-scale application potential.

Contribution

It introduces a phase-diagram for ferromagnetic layer configurations in Josephson junctions, aiding optimization for cryogenic memory applications.

Findings

Demonstrated phase control using two magnetic layer configurations.

Outlined issues for device optimization in large-scale arrays.

Proposed a phase diagram for material thickness combinations.

Abstract

Josephson junctions containing ferromagnetic materials have attracted intense interest both because of their unusual physical properties and because they have potential application for cryogenic memory. There are two ways to store information in such a junction: either in the amplitude of the critical current or in the ground-state phase difference across the junction; the latter is the topic of this paper. We have recently demonstrated two different ways to achieve phase control in such junctions: the first uses junctions containing two magnetic layers in a "pseudo spin valve" configuration, while the second uses junctions containing three magnetic layers with non-collinear magnetizations. The demonstration devices, however, have not yet been optimized for use in a large-scale cryogenic memory array. In this paper we outline some of the issues that must be considered to perform such an optimization, and we provide a speculative "phase-diagram" for the nickel-permalloy spin-valve system showing which combinations of ferromagnetic layer thicknesses should produce useful devices.