[Paper Review] Recent progress and challenges in magnetic tunnel junctions with 2D materials for spintronic applications

Lishu Zhang, Jun Zhou+3 more|arXiv (Cornell University)|Feb 7, 2021

2D Materials and Applications173 references4 citations

TL;DR

This review synthesizes recent advances in magnetic tunnel junctions (MTJs) incorporating two-dimensional (2D) materials, highlighting their potential for next-generation spintronic devices. It examines 2D materials like graphene, h-BN, MoS2, CrI3, and Fe3GeTe2 as electrodes or tunneling barriers, emphasizing their high spin polarization, atomic thinness, and tunability to overcome limitations in conventional MTJs, with key challenges including interface quality, material stability, and scalability.

ABSTRACT

As Moore's law is gradually losing its effectiveness, developing alternative high-speed and low-energy-consuming information technology with post-silicon advanced materials is urgently needed. The successful application of tunneling magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) has given rise to a tremendous economic impact on magnetic informatics, including MRAM, radio-frequency sensors, microwave generators and neuromorphic computing networks. The emergence of two-dimensional (2D) materials brings opportunities for MTJs based on 2D materials which have many attractive characters and advantages. Especially, the recently discovered intrinsic 2D ferromagnetic materials with high spin-polarization hold the promise for next-generation nanoscale MTJs. With the development of advanced 2D materials, many efforts on MTJs with 2D materials have been made both theoretically and experimentally. Various 2D materials, such as semi-metallic graphene, insulating h-BN, semiconducting MoS2, magnetic semiconducting CrI3, magnetic metallic Fe3GeTe2 and some other recently emerged 2D materials are discussed as the electrodes and/or central scattering materials of MTJs in this review. We discuss the fundamental and main issues facing MTJs, and review the current progress made with 2D MTJs, briefly comment on work with some specific 2D materials, and highlight how they address the current challenges in MTJs, and finally offer an outlook and perspective of 2D MTJs.

Motivation & Objective

• To evaluate the potential of 2D materials in enabling ultrathin, low-power magnetic tunnel junctions (MTJs) for post-silicon spintronic applications.
• To identify and analyze the fundamental challenges in integrating 2D materials into functional MTJs, including interface scattering, tunneling barrier quality, and material stability.
• To assess the performance of various 2D materials—such as graphene, h-BN, MoS2, CrI3, and Fe3GeTe2—as electrode or barrier materials in MTJs.
• To highlight recent experimental and theoretical progress in achieving high tunneling magnetoresistance (TMR) in 2D MTJs.
• To provide a forward-looking perspective on the integration of intrinsic 2D ferromagnets and advanced 2D heterostructures in next-generation spintronic devices.

Proposed method

• Systematic review of theoretical and experimental studies on MTJs incorporating 2D materials, focusing on material selection and device architecture.
• Analysis of electronic and magnetic properties of 2D materials, including spin polarization, band structure, and interfacial coupling at heterojunctions.
• Evaluation of tunneling transport mechanisms in 2D MTJs using non-equilibrium Green's function (NEGF) and density functional theory (DFT) simulations.
• Comparison of TMR performance across different 2D material combinations, emphasizing interface quality and barrier transparency.
• Discussion of fabrication techniques such as mechanical exfoliation, chemical vapor deposition (CVD), and van der Waals heteroepitaxy for 2D MTJ integration.
• Assessment of device scalability, thermal stability, and energy efficiency based on material characteristics and simulation results.

Experimental results

Research questions

• RQ1 How do the intrinsic spin-polarized properties of 2D ferromagnetic materials like CrI3 and Fe3GeTe2 enhance tunneling magnetoresistance in MTJs?
• RQ2 What are the dominant scattering and interface effects limiting TMR performance in 2D MTJs, and how can they be mitigated?
• RQ3 To what extent can 2D materials such as graphene and h-BN serve as ideal tunneling barriers or electrodes in spintronic MTJs?
• RQ4 What are the key challenges in achieving reproducible, high-performance 2D MTJs at the nanoscale, particularly in terms of material quality and integration?
• RQ5 How do the electronic and magnetic properties of 2D heterostructures influence the overall device functionality and scalability in spintronic applications?

Key findings

• Intrinsic 2D ferromagnetic materials like CrI3 and Fe3GeTe2 exhibit high spin polarization, enabling potential for high TMR in ultrathin MTJs.
• Graphene and hexagonal boron nitride (h-BN) demonstrate excellent tunneling properties due to their atomically thin, defect-free structures, supporting high TMR ratios.
• Semiconducting 2D materials such as MoS2 show tunable bandgaps and spin-dependent transport, enabling potential for spin-filtering and logic applications.
• Experimental and theoretical studies report TMR values exceeding 100% in selected 2D MTJs, particularly with CrI3-based heterostructures.
• Interface quality and interfacial scattering remain the primary bottlenecks, significantly reducing TMR efficiency despite promising material properties.
• The integration of 2D materials into MTJs offers a pathway toward sub-10 nm devices with low power consumption and high speed, essential for neuromorphic and MRAM applications.