Exploring the interplay between exchange coupling and Dzyaloshinskii–Moriya interaction in synthetic antiferromagnets for domain wall applications

The increasing demand for data storage is pushing conventional charge-based memory technologies toward their fundamental limits. Spintronic devices offer a promising alternative by combining non-volatility, fast operation, and high integration density. Spintronics has already enabled several important technologies, ranging from hard-disk-drive (HDD) read heads to Magnetic Random-Access Memory (MRAM).

MRAM relies on Magnetic Tunnel Junctions (MTJs), where information is stored in the magnetic state of a ferromagnetic layer and read through the Tunnelling Magnetoresistance (TMR) effect. In Spin-Transfer-Torque MRAM (STT-MRAM), writing requires current to flow through the tunnel barrier, leading to relatively high switching currents and potential reliability limitations. Spin-Orbit-Torque MRAM (SOT-MRAM) addresses these limitations by separating the read and write paths, enabling fast switching and improved endurance. However, switching the entire magnetic layer still requires substantial energy, while achieving reliable field-free switching remains a major challenge.

Single-bit domain-wall (DW) devices offer an alternative approach by encoding information in the position of a DW within an extended magnetic layer. Instead of reversing the entire magnetic layer, only the DW needs to be displaced, potentially reducing the switching energy. In addition, DW motion can enable field-free operation, making DW-based devices an attractive approach for scalable and energy-efficient spintronic memory.

At imec, we have demonstrated full electrical control of nanoscale DWs using MTJs for both writing and reading. This work provides an important proof-of-concept for the electrical manipulation of DWs in highly scaled devices [1]. Building on this achievement, we are currently investigating synthetic antiferromagnets (SAFs) as DW track materials for nanoscale devices. SAFs are particularly attractive for current-driven DW motion because they can enable fast and efficient propagation while reducing sensitivity to external magnetic fields and stray-field interactions. Recently, we also demonstrated an electrical TMR-based approach for selectively probing the magnetization state of SAFs. This work demonstrates the feasibility of electrically characterizing SAF magnetic states at the nanoscale and provides an important tool for studying and optimizing SAF-based DW devices [2].

However, the implementation of SAFs in nanoscale DW devices raises fundamental questions regarding the interplay between antiferromagnetic exchange coupling, the Dzyaloshinskii–Moriya interaction (DMI), and spin–orbit torque (SOT). These interactions play a critical role in determining the efficiency and reliablity of current-driven DW motion, yet their interdependence in SAF systems is not fully understood.

This internship project aims to investigate the influence of antiferromagnetic exchange coupling on the DMI in SAFs. The DMI will first be quantitatively characterized through electrical measurements on Hall-bar devices incorporating different SAF material stacks. By correlating the extracted DMI with the exchange coupling strength and magnetic properties of the SAFs, the project will establish a better understanding of the interplay between these key material parameters.

The study will then be extended to nanoscale Hall-bar devices to investigate scaling effects. In particular, fabrication-induced edge roughness and other nanoscale effects may modify the exchange coupling and magnetic properties of the SAF, potentially affecting DW dynamics and switching behavior. The project will therefore establish a link between material properties, exchange coupling and DMI, providing valuable insights for the development of efficient and scalable SAF-based domain-wall devices.

References:

1.  https://www.imec-int.com/en/articles/imec-brings-magnetic-domain-wall-devices-closer-industrial-reality

2. Giuliano et al., Phys. Rev. Appl. 25, 034083 (2026)