Periodic Co/Nb pseudo spin valve for cryogenic memory.

Nikolay Klenov,Yury Khaydukov,Igor Soloviev,Vladimir Boian,Mikhail Kupriyanov,Thomas Keller,Sergey Bakurskiy,Roman Morari,Bernhard Keimer,Anatoli Sidorenko

doi:10.3762/bjnano.10.83

Abstract

We present a study of magnetic structures with controllable effective exchange energy for Josephson switches and memory applications. As a basis for a weak link we propose to use a periodic structure composed of ferromagnetic (F) layers spaced by thin superconductors (s). Our calculations based on the 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 the magnetic alignment we propose to use a periodic system whose unit cell is a pseudo spin valve of structure F1/s/F2/s where F1 and F2 are two magnetic layers having different coercive fields. In order to check the feasibility of controllable switching between AP and P states through the whole periodic structure, we prepared a superlattice [Co(1.5 nm)/Nb(8 nm)/Co(2.5 nm)/Nb(8 nm)]6 between two superconducting layers of Nb(25 nm). Neutron scattering and magnetometry data showed that parallel and antiparallel alignment can be controlled with a magnetic field of only several tens of Oersted.

Highlights

The utilization of the competition and coexistence of superconducting (S) and ferromagnetic (F) correlations could provide an increase in the performance and degree of integration for cryogenic memory storage devices and synaptic elements [1,5,6,7,8,9,10,11,12,13,14,15,16]
These ideas can be implemented through a Josephson contact with two stable states: a high value of the critical current, IC, corresponds to the ”open” state and a low value to the ”closed” state. Such a device can be assembled if the weak link is a composite F/N/F trilayer (N is a normal metal) whose magnetic state can be switched between parallel and antiparallel directions of the magnetization vectors of the F layers [7]
For the AP orientation of the magnetization vectors of the F layers, an additional mechanism arises for the renormalization of the effective exchange energy, which leads to its further decrease [23,24,25]

Summary

Introduction

Such a device can be assembled if the weak link is a composite F/N/F trilayer (N is a normal metal) whose magnetic state can be switched between parallel and antiparallel directions of the magnetization vectors of the F layers [7]. For the AP orientation of the magnetization vectors of the F layers, an additional mechanism arises for the renormalization of the effective exchange energy, which leads to its further decrease [23,24,25].

Objectives

Results

Conclusion