Experimental demonstration of a Josephson magnetic memory cell with a programmable \pi-junction

TL;DR

This paper demonstrates a Josephson magnetic memory cell using a NiFe/Cu/Ni pseudo spin-valve junction that can be switched between zero and pi states, paving the way for scalable superconducting cryogenic memory.

Contribution

It experimentally shows how to control the phase state of a Josephson junction with magnetic states, introducing a new approach for superconducting memory devices.

Findings

Memory states mapped onto zero or pi phase states.

Switching between states achieved with ~5 mT magnetic fields.

First demonstration of a programmable pi-junction in a magnetic Josephson device.

Abstract

We experimentally demonstrate the operation of a Josephson magnetic random access memory unit cell, built with a Ni_80Fe_20/Cu/Ni pseudo spin-valve Josephson junction with Nb electrodes and an integrated readout SQUID in a fully planarized Nb fabrication process. We show that the parallel and anti-parallel memory states of the spin-valve can be mapped onto a junction equilibrium phase of either zero or pi by appropriate choice of the ferromagnet thicknesses, and that the magnetic Josephson junction can be written to either a zero-junction or pi-junction state by application of write fields of approximately 5 mT. This work represents a first step towards a scalable, dense, and power-efficient cryogenic memory for superconducting high-performance digital computing.