次世代スピントロニクスの道を拓く反強磁性トンネル接合（Interface-controlled Antiferromagnetic Tunnel Junctions Offer New Path for Next-generation Spintronics）

2025-07-29 中国科学院(CAS)

Antiferromagnetic tunnel junction with interface-driventunneling magnetoresistance (Image by SHAO Dingfu)

＜関連情報＞

• https://english.cas.cn/newsroom/research_news/phys/202508/t20250801_1048946.shtml
• https://www.cell.com/newton/fulltext/S2950-6360(25)00134-3
• https://www.cell.com/newton/fulltext/S2950-6360(25)00185-9

界面制御型反強磁性トンネル接合部 Interface-controlled antiferromagnetic tunnel junctions

Liu Yang ∙ Yuan-Yuan Jiang ∙ Xiao-Yan Guo ∙ … ∙ Yu-Ping Sun ∙ Evgeny Y. Tsymbal ∙ Ding-Fu Shao
Newton  Published:June 23, 2025
DOI:https://doi.org/10.1016/j.newton.2025.100142

Accessible overview

Spintronics—a technology leveraging electron spin for faster, more efficient electronics—primarily relies on magnetic tunnel junctions (MTJs). While traditional MTJs use ferromagnets, switching to antiferromagnetic (AFM) materials could significantly boost device speed and storage density. Most AFM tunnel junctions (AFMTJs) to date have focused on spin-filtering barriers or bulk spin-dependent currents. This work highlights a promising, yet underexplored, approach: using certain AFM metals, such as doped Fe₄GeTe₂, with magnetically active interfaces to generate strong spin-polarized currents and sizable tunneling magnetoresistance (TMR). Advanced simulations demonstrate that this design achieves a large negative TMR controlled solely by interface-driven spin currents. Crucially, these AFMTJs enable easy switching of the Néel vector, offering a practical route to ultrafast, high-density spintronic devices. This research broadens the toolkit for next-generation memory and computing and redefines how antiferromagnets can be harnessed by exploiting their often-overlooked interfacial properties—marking a step toward energy-efficient, scalable spin-based technologies.

Highlights

• Interface-driven tunneling magnetoresistance achieved in antiferromagnetic tunnel junctions
• Robust interface-driven spin currents demonstrated in van der Waals A-type antiferromagnets
• Doped Fe_nXTe₂ (X = Ge, Ga) systems are potential antiferromagnetic electrodes

Summary

Magnetic tunnel junctions (MTJs) are essential components of high-performance spintronic devices. While conventional MTJs use ferromagnetic materials, antiferromagnetic (AFM) compounds can significantly increase operation speed and packing density. Current AFM tunnel junctions (AFMTJs) exploit antiferromagnets as spin-filter barriers or metal electrodes with bulk spin-dependent currents. Here, we highlight a largely overlooked AFMTJ prototype with bulk-spin-degenerate electrodes exhibiting A-type AFM stacking, forming magnetically uncompensated interfaces that enable spin-polarized tunneling currents and a sizable tunneling magnetoresistance (TMR). Using first-principles quantum-transport calculations and van der Waals (vdW) metal Fe₄GeTe₂ as an example, we demonstrate a large negative TMR from interfacial magnetic moment alignment. This prototype can also be realized with non-vdW A-type AFM metals featuring roughness-insensitive surface magnetization. Beyond TMR, these AFMTJs allow convenient switching of the Néel vector, opening new avenues for AFM spintronics based on interface-driven spin-dependent properties.

補償されていない反強磁性界面がファンデルワールス接合に新たな可能性を開く Uncompensated antiferromagnetic interfaces unlock new possibilities in van der Waals junctions

Jose L. Lado ∙ Saroj P. Dash
Newton  Published:June 22, 2025
DOI:https://doi.org/10.1016/j.newton.2025.100193

Abstract

Unlike conventional ferromagnetic systems, antiferromagnets offer benefits such as zero stray fields and ultrafast dynamics. Using first-principles calculations, Yang et al. further discover that the uncompensated interface magnetization of antiferromagnetic electrodes leads to a significant tunneling magnetoresistance, offering new design principles for spintronic technologies.

Main text

Hybrid materials based on magnetic systems offer highly versatile platforms for controlling electric currents. A paradigmatic example is tunneling magnetoresistance (TMR), where the magnetic alignment between electrodes enables a significant change in the electrical resistance of a junction. These devices have been instrumental in electronic technology and continue to serve as a cornerstone for future spintronic applications.

Van der Waals materials provide an alternative platform to bulk compounds for creating electronic devices with novel functionalities. Their two-dimensional nature facilitates the easy formation of interfaces between materials, owing to the weak van der Waals forces. Interestingly, these weak forces also enable precise control over the twist angle between materials, allowing for the tuning of interface properties and the emergence of new correlated phases. While the critical temperatures of magnetic order of van der Waals materials are often lower than those in bulk counterparts, spintronic devices based on van der Waals materials can play a crucial role in low-temperature control electronics, which are essential for future cryogenic spin and quantum technologies. Ultimately, the development of van der Waals ferromagnetic and antiferromagnetic materials with critical temperatures above room temperature would expand their applications in ambient temperatures.

Van der Waals materials exhibiting magnetic order have been successfully isolated in the monolayer limit. The first examples include monolayers of Fe₂GeTe₃,¹ CrBr₃,² and CrI₃,³ which develop out-of-plane ferromagnetic order due to uniaxial anisotropy, while CrCl₃⁴ exhibits in-plane ferromagnetism. While these ferromagnets have relatively low critical temperatures, compounds such as Fe_xGeTe₂ and Fe_xGaTe₂ have recently emerged as promising candidates for higher-temperature magnetism, potentially beyond room temperature. These materials serve as a promising starting point for engineering other higher-temperature phases through alloying with different elements, enabling the creation of both ferromagnetic and antiferromagnetic van der Waals compounds.⁵

A study in Newton conducted by an international collaboration led by Ding-Fu Shao from the Chinese Academy of Sciences introduces a prototype of antiferromagnetic tunnel junctions based on interface effects.⁶ Unlike conventional magnetic tunnel junctions (MTJs), which rely on ferromagnets, their proposal focuses on utilizing antiferromagnets. The use of antiferromagnets in MTJs offers several promising advantages over ferromagnets, including zero stray fields due to compensated magnetic moments and ultrafast THz-regime magnetization dynamics.

Antiferromagnets have been employed in spintronics through various strategies, two of which are particularly relevant here. The first involves using antiferromagnetic insulators as spin filters, where magnetic switching is leveraged to achieve TMR. The second relies on exploiting spin-dependent bulk electronic properties in metallic antiferromagnets for TMR. The researchers propose an alternative strategy that uses a specific type of antiferromagnetic stacking. This approach creates magnetically uncompensated interfaces that generate spin-polarized tunneling currents, even as the bulk remains compensated.

The researchers based their analysis on first-principle and quantum-transport calculations, focusing on heterostructures built from Fe₄GeTe₂. While pristine Fe₄GeTe₂ is ferromagnetic, it can be switched to an A-type antiferromagnetic state through co-doping. The study specifically examined interfaces with hBN, where their calculations revealed the emergence of significant spin polarization (Figure 1).⁶ This interfacial polarization leads to sizable magnetoresistance. The researchers also propose applications in antiferromagnetic memories, where data are written using spin torques and read via TMR devices: MTJs. Specifically, such magnetic junctions can be useful for readout in spin-orbit torque-based magnetic memory devices employing van der Waals heterostructures.⁷