Periodic Co/Nb pseudo spin-valve for cryogenic memory

TL;DR

This paper introduces a periodic ferromagnetic/superconducting structure for cryogenic memory, demonstrating controllable magnetic states that significantly influence Josephson junction critical currents, with experimental validation of magnetic switching.

Contribution

It proposes a novel periodic pseudo spin-valve structure for cryogenic memory and demonstrates controllable magnetic alignment using modest magnetic fields.

Findings

Switching from P to AP alignment enhances critical current.

Neutron scattering confirms magnetic state control with small magnetic fields.

Superlattice structure is feasible for cryogenic memory applications.

Abstract

We present a new study of magnetic structures with controllable effective exchange energy for Josephson switches and memory. As a basis for a weak link we propose to use a periodic structure comprised of ferromagnetic (F) layers spaced by thin superconductors (s). Our calculations based on Usadel equations show that switching from parallel (P) to antiparallel (AP) alignment of neighboring F layers can lead to a significant enhancement of the critical current through the junction. To control magnetic alignment we propose to use periodic system where unit cell is a pseudo spin-valve $F_1$/s/$F_2$/s with $F_1$ and $F_2$ two magnetic layers having different coercive fields. In order to check feasibility of controllable switching between AP and P states through the \emph{whole} periodic structure we prepared a superlattice [Co(1.5nm)/Nb(8nm)/Co(2.5nm)/Nb(8nm)]$_6$ between two superconducting layers of Nb(25nm). Neutron scattering showed that parallel and antiparallel alignment can be organized by using of magnetic fields of only several tens of Oersted.