Two-dimensional (2D) magnets, with their atomic thickness, exhibit intriguing physical properties such as interlayer magnetic coupling, perpendicular magnetic anisotropy, and tunable spin transport, offering a unique platform for exploring low-dimensional magnetism and developing novel spintronic devices. Recent research on 2D magnets has primarily focused on Cr, Mn, and Fe-based material systems. Among them, Fe-based materials (FeₙGeTe₂, n=3,4,5) have attracted significant attention due to their high bulk Curie temperature (200-300 K), layered structure, and chemical stability. However, the application of Fe-based 2D magnets still faces challenges, such as overcoming demagnetization issues for next-generation magnetic memory devices and effectively doping high-density electrons into few-layer Fe₃GeTe₂ to enhance the Curie temperature.
Methods
To address these challenges, Prof. Liang Hu and Prof. Ling-Wei Li's team at Hangzhou Dianzi University employed a synchronized electrochemical exfoliation and electron doping strategy. By utilizing soft organic cations, they achieved the scalable fabrication of few-layer Fe₃GeTe₂ nanoflakes. A constant current was applied in an electrochemical cell, driving organic TBA⁺ cations to intercalate into the Fe₃GeTe₂ single crystal, expanding the interlayer spacing and ultimately exfoliating the material. The exfoliated 2D material was further subjected to sonication and centrifugation to obtain high-quality superlattice nanoflakes.
Highlights
Scalable fabrication of ultrathin Fe₃GeTe₂ superlattice nanoflakes: This method enables the efficient fabrication of Fe₃GeTe₂ superlattice nanoflakes with a thickness of only 6 nm.
Giant electron doping: Compared to conventional methods, this approach achieves a higher electron doping level (~1.15 e⁻/f.u.), effectively enhancing the Curie temperature of the material. Competitive Curie temperature and magnetic anisotropy constant: The exfoliated Fe₃GeTe₂ superlattice nanoflakes exhibit a Curie temperature as high as 385 K and significant magnetic anisotropy, making them competitive among 2D magnets. Rapid evaluation of doping uniformity via vertical magnetization shift effect: This study identified a vertical magnetization shift effect that can be used to rapidly assess the doping uniformity in 2D magnets, providing new insights for optimizing the fabrication process of 2D magnets.
This research provides a new perspective for understanding the role of parasitic charges in 2D magnetism and offers new strategies for developing novel spintronic devices based on 2D magnets. For example, the fabricated Fe₃GeTe₂ superlattice nanoflakes hold potential applications in magnetic sensors, memory devices, and spin field-effect transistors.
Fig. 1. Theoretical calculations and magnetic origin of the intercalated Fe₃GeTe₂
Fig. 2. Vertical magnetization shift phenomena and its schematic demonstration
Authors
The first author and corresponding author of this work are Prof. Liang Hu and Prof. Ling-Wei Li from Hangzhou Dianzi University, respectively.
L. Hu, B. Yang, Z. Hou, Y. Lu, W. Su, L. Li, Unlocking the charge doping effect in softly intercalated ultrathin ferromagnetic superlattice, eScience 3(3) (2023) 100117. DOI: https://doi.org/10.1016/j.esci.2023.100117
