Readable Racetrack Memory via Ferromagnetically Coupled Chiral Domain Walls

TL;DR

This paper proposes a new readable racetrack memory design using ferromagnetically coupled chiral domain walls in a synthetic multilayer, achieving high speed, density, and readability for magnetic memory applications.

Contribution

It introduces a novel multilayer structure with different DMI types that enhances domain wall velocity and readability, addressing challenges in SAF-based racetrack memories.

Findings

Increased domain wall velocity due to interlayer coupling.

Enhanced stray field improves readout capability.

Reduced minimum spacing between domain walls.

Abstract

Current-induced motion of domain walls (CIMDW) with interfacial Dzyaloshinskii-Moriya interaction (DMI) in heavy metal (HM)/ferromagnetic (FM) metal multilayers have attracted attention owing to their potential application in novel magnetic memories. In recent years, the CIMDW at ultrahigh speed has been observed in a synthetic antiferromagnetic (SAF) multilayer. However, due to the zero net magnetization, the reading of information from the SAF multilayer is still challenging. In this work, we propose a readable racetrack memory consisting of a synthetic ferromagnetic multilayer composed of two FM layers with an interlayer FM coupling. One FM layer had an isotropic DMI, while the other had an anisotropic DMI. This difference of DMIs resulted in the opposite tilting directions of the DW planes in the two layers. This tilting was inhibited by a strong interlayer FM coupling, resulting in an increase in the DW velocity and the reduction of the minimum allowed spacing between two adjacent DWs. In addition, the FM coupling enhanced the stray field, and the stored information could be read conveniently using a conventional reading head. Therefore, our proposal paves a way for the fabrication of a racetrack memory with high reading speed, large storage density, and good readability.