⇦Chinese Physics Letters, 2023, Vol. 40, No. 5, Article code 057301Review Development of Intrinsic Room-Temperature 2D Ferromagnetic Crystals for 2D Spintronics Wen Jin (靳雯)1,2, Gaojie Zhang (张高节)1,2, Hao Wu (武浩)1,2,3,4, Li Yang (杨丽)1,2, Wenfeng Zhang (张文峰)1,2,3, and Haixin Chang (常海欣)1,2,3,4* Affiliations 1Center for Joining and Electronic Packaging, State Key Laboratory of Material Processing and Die & Mold Technology, School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China 2Shenzhen R&D Center of Huazhong University of Science and Technology, Shenzhen 518000, China 3Institute for Quantum Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China 4Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China Received 2 March 2023; accepted manuscript online 27 March 2023; published online 20 April 2023 *Corresponding author. Email: hxchang@hust.edu.cn Citation Text: Jin W, Zhang G J, Wu H et al. 2023 Chin. Phys. Lett. 40 057301    Abstract Two-dimensional (2D) ferromagnetic crystals with fascinating optical and electrical properties are crucial for nanotechnology and have a wide variety of applications in spintronics. However, low Curie temperatures of most 2D ferromagnetic crystals seriously hinder their practical applications, thus searching for intrinsic room-temperature 2D ferromagnetic crystals is of great importance for development of information technology. Fortunately, progresses have been achieved in the last few years. Here we review recent advances in the field of intrinsic room-temperature 2D ferromagnetic crystals and introduce their applications in spintronic devices based on van der Waals heterostructures. Finally, the remaining challenge and future perspective on the development direction of intrinsic room-temperature 2D ferromagnetic crystals for 2D spintronics and van der Waals spintronics are briefly summarized.
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 DOI:10.1088/0256-307X/40/5/057301 © 2023 Chinese Physics Society Article Text Quest for Intrinsic Room-Temperature 2D Ferromagnetic Crystals. The atomically thin nature and fascinating physical properties of two-dimensional (2D) crystals have provided opportunities for fundamental physics and made them the mainstay of nanotechnology.[1-5] With the development of information technology, spintronics has aroused great interest as it reduces the power consumption and enhances the processing capabilities of electronic devices by utilizing the spin degree of freedom of carriers.[6,7] Thus, spintronics based on 2D crystals is of significant importance and has great potential in next-generation spintronic devices. Theoretically, long-range magnetic order is hard to exist in 2D crystals at finite temperatures due to the enhancement of thermal fluctuations according to the Mermin–Wagner theorem.[8] However, the discovery of van der Waals (vdW) CrI$_{3}$[9] and Cr$_{2}$Ge$_{2}$Te$_{6}$[10] with intrinsic ferromagnetism in 2017 proved that magnetic anisotropy can effectively suppress the fluctuations by opening a spin-wave excitation gap, thus, realize ferromagnetism in 2D crystals. Together with the subsequent reports on other 2D ferromagnetic crystals, such as Fe$_{3}$GeTe$_{2}$,[11] CrCl$_{3}$,[12] and CrBr$_{3}$,[13,14] these 2D ferromagnetic crystals have opened a new window for 2D spintronics applied in magnetic storage and logic operation. However, the Curie temperatures ($T_{\rm C}$) of them are mostly below room-temperature (33–220 K), hindering their practical applications. Great efforts have been made to search for 2D ferromagnetic crystals with $T_{\rm C}$ at or above room temperature. For instance, Bonilla et al.[15] reported the above-room-temperature ferromagnetism in monolayer VSe$_{2}$ grown on graphite or MoS$_{2}$ substrates by molecular beam epitaxy. However, some reports provided opposite results where no ferromagnetism was observed in VSe$_{2}$.[16,17] Other non-intrinsic room-temperature ferromagnetic crystals have been explored through various methods such as ionic gate doping,[18] doping with defects or impurities,[19-21] strain,[22] proximity effects,[23,24] and substrate interfacial interaction,[25] which are not easily manipulated as intrinsic ferromagnetism and increase the challenge for practical applications in spintronic devices. A strategy to induce intrinsic ferromagnetism in 2D crystals is via magnetic element doping. For example, Yang et al.[26] developed a two-step Te flux method to introduce near-room temperature intrinsic ferromagnetism in WTe$_{2}$ by Cr doping. The $T_{\rm C}$ (182–283 K) and magnetic moment (2.26–4.20 emu/g) can be effectively adjusted with Cr concentration changing. The semimetallic behavior of $T_{d}$-WTe$_{2}$ was largely retained in Cr-WTe$_{2}$, a combination of type-II Weyl semimetal with ferromagnetism realized in vdW crystals for the first time, opening up opportunities for the investigation of magnetic control topology in vdW materials. Another work of MoTe$_{2}$ doping with Cr atoms also showed intrinsic ferromagnetism with $T_{\rm C} \sim 220$ K for 2–5 nm nanosheets.[27] However, the amounts of magnetic elements doped into the host crystals are very limited, resulting in relatively low saturation magnetization.
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Fig. 1. Ferromagnetic properties and structural characterizations of 2D CrTe$_{2}$ crystals. (a) Spatially resolved magnetometry. Focused Kerr measurements performed in longitudinal geometry and at room temperature on three CrTe$_{2}$ flakes having different thicknesses, as indicated in the atomic force microscope (AFM) image. On the thinnest flake (10 nm, green), no magnetic signal is found, whereas a Kerr signal is clearly seen for flakes with thicknesses of 30 nm (red), 80 nm (blue), 100 nm (purple and red), and 125 nm (yellow). In all the cases, the hysteresis loops show strong remanence, close to 100%, and a coercivity of a few millitesla only. Reproduced with permission.[28] Copyright 2020, American Chemical Society. (b) AFM topographic image and corresponding height profile of a typical few-layered 1T-CrTe$_{2}$. (c) Schematics of the crystal structure of 1T-CrTe$_{2}$. (d) Faraday rotation of 5-nm Pt thin film protected CrTe$_{2}$ flake with several thicknesses, with data obtained at 10 K. For thin samples, signals are multiplied by a factor of 10 to fit the scale. Reproduced with permission.[29] Copyright 2020, Springer Nature.
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Fig. 2. Structural characterizations and ferromagnetic properties of 2D CrTe crystals. (a) Unit cell (UC) of NiAs-tape CrTe. (b) AFM images for 2D CrTe crystals with different thicknesses of $\sim$ $0.8$ nm (mono-UC), 2 nm (bi-UC), and 3 nm (tri-UC). (c) Ferromagnetic properties of multi-UC and few-UC CrTe crystals. (d) Anomalous Hall effect of 37 nm CrTe 2D crystals. (e) MFM phase angle difference in substrate, few-UC-1 ($\sim$ $3$ nm thick), and few-UC-2 ($\sim$ $3$ nm thick, stack on few-UC-1) CrTe crystals with side width from 10 to 300 nm. No external magnetic field is applied on few-UC CrTe during all the MFM tests. Error bars s.e.m.; $N= 30$. Reproduced with permission.[30] Copyright 2021, Springer Nature.
Alternatively, the $T_{\rm C}$ can be elevated by increasing the concentration of magnetic metal atoms in 2D vdW ferromagnetic crystals, such as Fe$_{3}$GeTe$_{2}$. May et al.[31] observed intrinsic ferromagnetism in Fe$_{5-x}$GeTe$_{2}$ 2D crystals with $T_{\rm C} \sim 280$ K for 12 nm nanosheets. Fe$_{4}$GeTe$_{2}$ reported by Seo et al.[32] exhibited a near-room-temperature ferromagnetic order ($T_{\rm C} \sim 270$ K) in 7 nm nanoflakes. The enhancement of $T_{\rm C}$ in such a system is contributed from the higher Fe concentrations, but at the sacrifice of magnetic anisotropy and coercivity. In particular, the ferromagnetic properties become very obscure when the temperature is above 200 K and most of the $T_{\rm C}$ will drop far below room temperature for the crystal thickness down to atomic limit. Significant progress of intrinsic room-temperature 2D ferromagnetic crystals preparation has been achieved in two types of 2D CrTe$_{x}$ crystals discovered almost in the same period independently by three groups. Purbawati et al.[28] prepared exfoliated flakes of 1T-CrTe$_{2}$ and revealed the room-temperature ferromagnetism ($T_{\rm C} =315$ K) in 1T-CrTe$_{2}$ crystals with an in-plane magnetic anisotropy. The ferromagnetism can be maintained in 30–100 nm thin sheets at room temperature [Fig. 1(a)]. Meanwhile, Sun et al.[29] obtained 2D 1T-CrTe$_{2}$ crystals via mechanical exfoliation and demonstrated that the $T_{\rm C}$ above 300 K can be maintained in few-layered nanoflakes down to 10 nm [Fig. 1(d)]. At the same time, Wu et al.[30] developed a CVD-assisted ultrasonication method to prepare freestanding ultrathin 2D CrTe crystals with thickness down to 0.8 nm (mono-unit cell). The 2D CrTe crystals showed above-room-temperature ferromagnetism with $T_{\rm C} \sim 367$ K for 20–40 nm nanosheets and $\sim$ $350$ K for 2–4 nm nanosheets [Figs. 2(c) and 2(d)]. In contrast with vdW ferromagnetic crystals, the $T_{\rm C}$ of 2D CrTe nanosheets is higher than that of the bulk counterparts ($T_{\rm C} \sim 343$ K), which can be attributed to 2D quantum confinement-induced enhancement of spin polarization with reduction of dimension. Moreover, compared with conventional ferromagnetic materials such as Fe, Co, Ni, and BaFe$_{12}$O$_{19}$, the 2D CrTe crystals exhibit comparable or better saturation magnetic moment and coercivity, showing the potential for utilizing in room-temperature integrated 2D spintronic devices.
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Fig. 3. Magneto-transport measurements, thickness-dependent and angle-dependent anomalous Hall effects in single-sheet 2D Fe$_{3}$GaTe$_{2}$ crystals. (a) Schematic and measurement geometry (thickness-dependent) of the Fe$_{3}$GaTe$_{2}$ Hall device. (b) Optical image and height profile of the few-layer Fe$_{3}$GaTe$_{2}$ Hall device. (c) Temperature-dependent longitudinal resistance of Fe$_{3}$GaTe$_{2}$ nanosheets with different thicknesses. Longitudinal resistances are normalized by their values at 300 K. Hall resistance ($R_{xy}$) at 3 K (d) and at 300 K (e) obtained in Fe$_{3}$GaTe$_{2}$ nanosheets with different thickness. (f) High temperature ($> 300$ K) AHE in 9.5 nm few-layer Fe$_{3}$GaTe$_{2}$. (g) Normalized remanent anomalous Hall resistance ($R_{xy}$) as a function of temperature in Fe$_{3}$GaTe$_{2}$ nanosheets with different thicknesses. $R_{xy}$ data are normalized by their values at 3 K. Inset shows the enlarged image from 340 to 390 K and the arrows mark the $T_{\rm C}$. Error bars s.d., $N = 25$. (h) Schematic and measurement geometry (angle-dependent) of the few-layer Fe$_{3}$GaTe$_{2}$ Hall device. (i) Angle-dependent Hall resistance ($R_{xy}$) of a Fe$_{3}$GaTe$_{2}$ few-layer nanosheet (9.5 nm) at 300 K. Inset shows the $\theta_{_{\scriptstyle M}}$ as a function of $\theta_{\scriptscriptstyle{\rm B}}$. The solid line is the fitting curve, and the dashed line marks $\theta_{_{\scriptstyle M}}=\theta_{\scriptscriptstyle{\rm B}}$ that corresponds to $K_{\rm u} = 0$. (j) Comparison of $K_{\rm u}$ for some conventional PMA ferromagnetic film and vdW ferromagnetic crystals at 300 K. Reproduced with permission.[33] Copyright 2022, Springer Nature.
The discovery of 2D CrTe$_{x}$ crystals can be a big step for the research of intrinsic room-temperature 2D ferromagnetic crystals in spintronics. However, either the in-plane magnetic anisotropy or the non-vdW structure makes CrTe$_{x}$ difficult applied in vdW heterostructures for spintronic devices such as magnetic tunnel junctions (MTJs) and magnetic random-access memory (MRAM). The recent big progress to solve this issue is the discovery of 2D vdW room-temperature intrinsic ferromagnetic crystal Fe$_{3}$GaTe$_{2}$ with large perpendicular magnetic anisotropy (PMA). Zhang et al.[33] reported a 2D vdW ferromagnetic crystal Fe$_{3}$GaTe$_{2}$ prepared by a self-flux method. The $T_{\rm C}$ of the 2D Fe$_{3}$GaTe$_{2}$ crystals varying with different thicknesses is up to 380 K, which is a record-high temperature amongst intrinsic 2D vdW ferromagnetic crystals. A more recent test indicated a $T_{\rm C}$ of 2D Fe$_{3}$GaTe$_{2}$ even as high as or higher than 400 K. Figure 3 shows the magneto-transport measurements and thickness-dependent anomalous Hall device performance in single-sheet 2D Fe$_{3}$GaTe$_{2}$ crystals,[33] revealing a robust large PMA ($K_{\rm u} \sim 3.88 \times 10^{5}$ J/m$^{3}$ for a 9.5-nm-thick 2D nanoflake), which is even better than some widely used conventional ferromagnetic thin films such as CoFeB[34] ($2.1 \times 10^{5}$ J/m$^{3}$) and Co$_{2}$FeAl[35] ($1.3 \times 10^{5}$ J/m$^{3}$), and other 2D vdW ferromagnetic crystals such as CrTe$_{2}$[36] ($4.9 \times 10^{4}$ J/m$^{3}$), making Fe$_{3}$GaTe$_{2}$ the most promising candidate for room-temperature 2D spintronics such as spin valves or MTJs to compete with current commercial memory technology.
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Fig. 4. Ferromagnetic properties of 2D Cr$_{0.024}$Ga$_{0.976}$Te nanosheets with different thicknesses. (a)–(c) $M$–$T$ (ZFC-FC) curves of the Cr$_{0.024}$Ga$_{0.976}$Te NSs-10 (a), NSs-60 (b), and NSs-300 (c) at 0.1 T external magnetic field. Insets: representative AFM images for NSs-10, NSs-60, and NSs-300. (d)–(f) $M$–$H$ curves for the Cr$_{0.024}$Ga$_{0.976}$Te NSs-10 (d), NSs-60 (e), and NSs-300 (f) in the magnetic field range from $-5$ to 5 T under different temperatures. Insets: slightly below $T_{\rm C}$ $M$–$H$ hysteresis loops ranging from $-1$ to 1 T. (g) $T_{\rm C}$ comparison of the Cr$_{0.024}$Ga$_{0.976}$Te bulk crystals, NSs-10, NSs-60, and NSs-300. Error bars s.d.; $N = 3$. (h) and (i) Temperature dependence of $M_{\rm sat}$ (h) and $H_{\rm C}$ (i) for the Cr$_{0.024}$Ga$_{0.976}$Te bulk crystals, NSs-10, NSs-60, and NSs-300. Error bars s.d.; $N = 200$. Reproduced with permission.[37] Copyright 2021, Wiley-VCH GmbH.
Intrinsic room-temperature 2D ferromagnetic semiconductors are vital for electrical control of 2D ferromagnetism, opening up opportunities for magnetic storage, spin filtering and logic computation. Zhang et al.[37] prepared 2D vdW ferromagnetic semiconductor Cr$_{x}$Ga$_{1-x}$Te single crystals with large bandgap (1.62–1.66 eV) and room-temperature $T_{\rm C}$ ($\sim$ $314.9$ K for $\sim$ $4.8$ nm nanosheets, $\sim$ $329$ K for 46 nm nanosheets) (Fig. 4). The intrinsic ferromagnetism can be effectively tuned by the Cr content and the crystal thickness. Another room-temperature intrinsic 2D ferromagnetic semiconductor was reported by Cheng et al.[38] They grew air-stable non-vdW nonlayered semiconducting cobalt ferrite (CoFe$_{2}$O$_{4}$, CFO) nanosheets with bandgap of 1.48–1.82 eV by vdW epitaxy. Room-temperature ferromagnetism was observed in CFO nanosheets with thickness down to 3.8 nm [Fig. 5(d)]. The $T_{\rm C}$ of CFO was above 390 K for mixed nanosheets with different thicknesses, demonstrating the potential for commercial (273 to 343 K) and industrial (233 to 358 K) applications. Spintronic Devices Based on Intrinsic Room-Temperature 2D Ferromagnetic Crystals. The development of intrinsic room-temperature 2D ferromagnetic crystals greatly facilitate the realization of practical room-temperature 2D spintronic devices. The layered vdW nature of the ferromagnets enables them integrating with other 2D materials to build seamless heterostructures with clean and sharp interface, for example, various spin valves including metallic spin valves and MTJs.[39-44]
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Fig. 5. Structural, electrical and ferromagnetic properties of 2D CFO nanosheets. (a) The atomic model of CFO with spinel structure and its top view along the [111] zone axis. (b) $I_{\rm DS}$–$V_{\rm DS}$ curves of an 11.5-nm-thick CFO device measured at different temperatures from 300 K to 100 K with steps of 10 K. Inset: the corresponding in situ device schematic on mica substrate. (c) $I_{\rm DS}$–$V_{\rm DS}$ curves of a 23-nm-thick CFO vertical device, showing switchable behavior. Sweep directions are indicated by arrows. Inset: device schematic of CFO vertical device. (d) MOKE hysteresis loops of CFO nanosheets with variable thicknesses measured at room temperature under out-of-plane magnetic field. Sweep directions are indicated by arrows. Reproduced with permission.[38] Copyright 2022, Springer Nature.
Generally, a spin valve is formed with two ferromagnetic electrodes divided by a non-magnetic spacer, the operation of which is based on the difference in the density of states around the Fermi level of the ferromagnetic electrodes between spin-up and spin-down electrons. The spacer enables the two ferromagnetic electrodes to be flipped independently under magnetic field, leading to low-resistance ($R_{\rm P}$) and high-resistance ($R_{\rm AP}$) states under the parallel and antiparallel configuration, respectively. Recently, room-temperature all-2D vdW metallic spin valves have been developed based on 2D Fe$_{3}$GaTe$_{2}$ crystals. By applying 2D Fe$_{3}$GaTe$_{2}$ crystals as both of the top and down ferromagnetic electrodes, Jin et al.[39,40] fabricated Fe$_{3}$GaTe$_{2}$/MoS$_{2}$/Fe$_{3}$GaTe$_{2}$ heterojunctions and observed a typical room-temperature spin valve effect with magnetoresistance (MR) of 0.31% at 300 K and 15.89% at 2.3 K. Another metallic spin valve based on Fe$_{3}$GaTe$_{2}$/MoSe$_{2}$/Fe$_{3}$GaTe$_{2}$ heterojunction [Fig. 6(a)–Fig. 6(c)] prepared by Yin et al.[41] showed an MR of 3.7% and 37.7% at 300 K and 2 K, respectively. Meanwhile, room-temperature MTJs using other 2D vdW spacers were also reported. A big breakthrough is the successful fabrication of the all-2D vdW Fe$_{3}$GaTe$_{2}$/WSe$_{2}$/Fe$_{3}$GaTe$_{2}$ MTJ with large room-temperature magnetoresistance reported by Zhu et al.[42] The MTJ exhibited tunnelling effect with large tunnel magnetoresistance (TMR) of 85% at $T = 300$ K [Fig. 6(f)] and 164% at $T=10$ K, comparable to that of state-of-the-art conventional MTJs and very close to that of commercial MTJs. The high performance of the MTJ can be attributed to the long spin diffusion length and spin-preservation properties of the high-quality WSe$_{2}$ and highly spin-polarized Fermi surfaces of Fe$_{3}$GaTe$_{2}$.[43] Moreover, a record-high operating temperature up to 400 K amongst all vdW MTJs was observed, potentially revolutionizing the development of 2D spintronics. Another Fe$_{3}$GaTe$_{2}$-based MTJ using WS$_{2}$ as the barrier reported by Jin et al.[44] showed a TMR ratio up to 213% with a derived spin polarization of 72% at low temperature (10 K), which is the highest amongst all-2D vdW Fe$_{3}$GaTe$_{2}$-based MTJs. The TMR decreased with increasing temperature but retained up to 11% at room temperature. Furthermore, the polarity of TMR can be electrically tunable, varying from $+$213% to $-9$% with increasing bias current at 10 K [Fig. 6(i)], providing alternative routes for electronic control of the spin in 2D vdW spintronic devices.
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Fig. 6. Schematic demonstration, electronic and magneto-transport properties of 2D Fe$_{3}$GaTe$_{2}$-based metallic and tunneling spin valves. (a) Schematic of Fe$_{3}$GaTe$_{2}$/MoSe$_{2}$/Fe$_{3}$GaTe$_{2}$ metallic spin valves. (b) $I$–$V$ characteristics of the Fe$_{3}$GaTe$_{2}$/MoSe$_{2}$/Fe$_{3}$GaTe$_{2}$ device at 300 K. (c) Room-temperature resistance $R$ and MR versus perpendicular magnetic field $B$ of the Fe$_{3}$GaTe$_{2}$/MoSe$_{2}$/Fe$_{3}$GaTe$_{2}$ device at a constant bias current $I = 1$ µA. Reproduced with permission.[41] Copyright 2023, The Author(s). (d) Schematic of Fe$_{3}$GaTe$_{2}$/WSe$_{2}$/Fe$_{3}$GaTe$_{2}$ MTJs. (e) $I$–$V$ characteristics of the Fe$_{3}$GaTe$_{2}$/WSe$_{2}$/Fe$_{3}$GaTe$_{2}$ device at 300 K. (f) Room-temperature resistance $R$ and TMR versus perpendicular magnetic field $B$ of the Fe$_{3}$GaTe$_{2}$/WSe$_{2}$/Fe$_{3}$GaTe$_{2}$ device at a constant bias voltage $V = 50$ mV. Reproduced with permission.[42] Copyright 2022, Chinese Physics Letters. (g) Schematic of Fe$_{3}$GaTe$_{2}$/WS$_{2}$/Fe$_{3}$GaTe$_{2}$ MTJs. (h) $I$–$V$ characteristics of the Fe$_{3}$GaTe$_{2}$/WS$_{2}$/Fe$_{3}$GaTe$_{2}$ device at 10 K and 300 K, respectively. (i) The $I$-dependent TMR ratio for the Fe$_{3}$GaTe$_{2}$/WS$_{2}$/Fe$_{3}$GaTe$_{2}$ MTJ at 10 K. Reproduced with permission.[44] Copyright 2023, arXiv.
Summary and Outlook. In summary, the development of intrinsic room-temperature 2D ferromagnetic crystals has achieved significant progress in the last few years. However, the investigation of 2D spintronics is still in its infancy. Challenges and obstacles remain and need to be overcome in the future. Firstly, the 2D ferromagnetic crystals are mostly obtained by mechanical exfoliation, which is inefficient and hard to meet the wafer-scale requirements for industrial applications. Secondly, although room-temperature MTJs with TMR of 85% are obtained, more work still needs to be performed to fully realize the great potential of Fe$_{3}$GaTe$_{2}$ with highly spin polarized Fermi surface and to obtain MTJs superior to commercial ones. Moreover, more room-temperature spintronic devices such as magnetization switching from spin-orbit torques based on intrinsic room-temperature 2D ferromagnetic crystals are still missing. Finally, integration of room-temperature 2D vdW functional magnetic units for complex working spintronic memory or memory computation are still challenging. More efforts need to be devoted on development of room-temperature 2D spintronics and vdW spintronics. Acknowledgments. This work was supported by the National Key Research and Development Program of China (Grant No. 2022YFE0134600), the National Natural Science Foundation of China (Grant Nos. 52272152, 61674063, and 62074061), the Foundation of Shenzhen Science and Technology Innovation Committee (Grant Nos. JCYJ20210324142010030 and JCYJ20180504170444967), and the Fellowship of China Postdoctoral Science Foundation (Grant No. 2022M711234). References Electric Field Effect in Atomically Thin Carbon FilmsAtomically Thin MoS 2 : A New Direct-Gap SemiconductorElectrical Transport Properties of Polycrystalline Monolayer Molybdenum DisulfideThin partially reduced oxide-graphene films: structural, optical, and electrical propertiesHigh Performance Multilayer MoS2 Transistors with Scandium ContactsVan der Waals magnets: Wonder building blocks for two‐dimensional spintronics?Magnetism in two-dimensional van der Waals materialsAbsence of Ferromagnetism or Antiferromagnetism in One- or Two-Dimensional Isotropic Heisenberg ModelsLayer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limitDiscovery of intrinsic ferromagnetism in two-dimensional van der Waals crystalsHard magnetic properties in nanoflake van der Waals Fe3GeTe2Enhancement of interlayer exchange in an ultrathin two-dimensional magnetDirect observation of van der Waals stacking–dependent interlayer magnetismMagnon-assisted tunnelling in van der Waals heterostructures based on CrBr3Strong room-temperature ferromagnetism in VSe2 monolayers on van der Waals substratesElectronic Structure and Enhanced Charge-Density Wave Order of Monolayer VSe2Evidence of Spin Frustration in a Vanadium Diselenide Monolayer MagnetGate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2Ta Doping Enhanced Room‐Temperature Ferromagnetism in 2D Semiconducting MoTe2 NanosheetsVacancy-Induced Ferromagnetism of MoS2 NanosheetsMagnetism in semiconducting molybdenum dichalcogenidesEvidence of the Existence of Magnetism in Pristine VX2 Monolayers (X = S, Se) and Their Strain-Induced Tunable Magnetic PropertiesProximity-Induced Ferromagnetism in Graphene Revealed by the Anomalous Hall EffectProximity-induced ferromagnetism and chemical reactivity in few-layer VSe 2 heterostructuresRoom Temperature Ferromagnetism of Monolayer Chromium Telluride with Perpendicular Magnetic AnisotropyHighly Tunable Near‐Room Temperature Ferromagnetism in Cr‐Doped Layered Td‐WTe2Tunable and Robust Near-Room-Temperature Intrinsic Ferromagnetism of a van der Waals Layered Cr-Doped 2H-MoTe2 Semiconductor with an Out-of-Plane AnisotropyIn-Plane Magnetic Domains and Néel-like Domain Walls in Thin Flakes of the Room Temperature CrTe2 Van der Waals FerromagnetRoom temperature ferromagnetism in ultra-thin van der Waals crystals of 1T-CrTe2Strong intrinsic room-temperature ferromagnetism in freestanding non-van der Waals ultrathin 2D crystalsFerromagnetism Near Room Temperature in the Cleavable van der Waals Crystal Fe5 GeTe2Nearly room temperature ferromagnetism in a magnetic metal-rich van der Waals metalAbove-room-temperature strong intrinsic ferromagnetism in 2D van der Waals Fe3GaTe2 with large perpendicular magnetic anisotropyA perpendicular-anisotropy CoFeB–MgO magnetic tunnel junctionPerpendicular Magnetic Anisotropy of Full-Heusler Films in Pt/Co2 FeAl/MgO TrilayersRoom-temperature intrinsic ferromagnetism in epitaxial CrTe2 ultrathin filmsHighly‐Tunable Intrinsic Room‐Temperature Ferromagnetism in 2D van der Waals Semiconductor Cr x Ga1− x TeUltrathin ferrite nanosheets for room-temperature two-dimensional magnetic semiconductorsRoom-Temperature Spin-Valve Effect in Fe$_3$GaTe$_2$/MoS$_2$/Fe$_3$GaTe$_2$ 2D van der Waals Heterojunction DevicesRoom-temperature spin-valve devices based on Fe3 GaTe2 /MoS2 /Fe3 GaTe2 2D van der Waals heterojunctionsFe3 GaTe2 /MoSe2 ferromagnet/semiconductor 2D van der Waals heterojunction for room-temperature spin-valve devicesLarge Room-Temperature Magnetoresistance in van der Waals Ferromagnet/Semiconductor JunctionsTremendous tunneling magnetoresistance effects based on van der Waals room-temperature ferromagnet Fe3 GaTe2 with highly spin-polarized Fermi surfacesRoom-temperature and tunable tunneling magnetoresistance in Fe3GaTe2-based all-2D van der Waals heterojunctions with high spin polarization
[1] Novoselov K S, Geim A K, Morozov S V, Jiang D, Zhang Y, Dubonos S V, Grigorieva I V, and Firsov A A 2004 Science 306 666
[2] Mak K F, Lee C, Hone J, Shan J, and Heinz T F 2010 Phys. Rev. Lett. 105 136805
[3] Najmaei S, Amani M, Chin M L, Liu Z, Birdwell A G, O'Regan T P, Ajayan P M, Dubey M and Lou J 2014 ACS Nano 8 7930
[4] Alexandrov G N, Smagulova S A, Kapitonov A N, Vasil'eva F D, Kurkina I I, Vinokurov P V, Timofeev V B, and Antonova I V 2014 Nanotechnol. Russ. 9 363
[5] Das S, Chen H, Penumatcha A, and Appenzeller J 2013 Nano Lett. 13 100
[6] Zhang W, Wong P K J, Zhu R, and Wee A T S 2019 InfoMat 1 479
[7] Burch K S, Mandrus D, and Park J G 2018 Nature 563 47
[8] Mermin N D and Wagner H 1966 Phys. Rev. Lett. 17 1133
[9] Huang B V, Clark G, Navarro-Moratalla E, Klein D R, Cheng R, Seyler K L, Zhong D, Schmidgall E, McGuire M A, Cobden D H, Yao W, Xiao D, Jarillo-Herrero P, and Xu X D 2017 Nature 546 270
[10] Gong C, Li L, Li Z, Ji H, Stern A, Xia Y, Cao T, Bao W, Wang C, Wang Y, Qiu Z Q, Cava R J, Louie S G, Xia J, and Zhang X 2017 Nature 546 265
[11] Tan C, Lee J, Jung S G, Park T, Albarakati S, Partridge J, Field M R, McCulloch D G, Wang L, and Lee C 2018 Nat. Commun. 9 1554
[12] Klein D R, MacNeill D, Song Q, Larson D T, Fang S, Xu M, Ribeiro R A, Canfield P C, Kaxiras E, Comin R, and Jarillo-Herrero P 2019 Nat. Phys. 15 1255
[13] Chen W J, Sun Z Y, Wang Z J, Gu L H, Xu X D, Wu S W, and Gao C L 2019 Science 366 983
[14] Ghazaryan D A, Greenaway M T, Wang Z, Guarochico-Moreira V H, Vera-Marun I J, Yin J, Liao Y, Morozov S V, Kristanovski O, Lichtenstein A I, Katsnelson M I, Withers F, Mishchenko A, Eaves L, DUTTASINHA S, Novoselov K S, and Misra A K 2018 Nat. Electron. 1 344
[15] Bonilla M, Kolekar S, Ma Y, Diaz H C, Kalappattil V, Das R, Eggers T, Gutierrez H R, Phan M H, and Batzill M 2018 Nat. Nanotechnol. 13 289
[16] Feng J G, Biswas D, Rajan A, Watson M D, Mazzola F, Clark O J, Underwood K, Marković I, McLaren M, Hunter A, Burn D M, Duffy L B, Barua S, Balakrishnan G, Bertran F, Le F P, Kim T K, van der Laan G, Hesjedal T, Wahl P, and King P D C 2018 Nano Lett. 18 4493
[17] Wong P K J, Zhang W, Bussolotti F, Yin X, Herng T S, Zhang L, Huang Y L, Vinai G, Krishnamurthi S, Bukhvalov D W, Zheng Y J, Chua R, N'Diaye A T, Morton S A, Yang C Y, Ou Y K H, Torelli P, Chen W, Goh K E J, Ding J, Lin M T, Brocks G, de Jong M P, Castro N A H, and Wee A T S 2019 Adv. Mater. 31 1901185
[18] Deng Y J, Yu Y J, Song Y C, Zhang J Z, Wang N Z, Sun Z, Yi Y F, Wu Y Z, Wu S, Zhu J, Wang J, Chen X H, and Zhang Y 2018 Nature 563 94
[19] Yang L, Wu H, Zhang W, Lou X, Xie Z, Yu X, Liu Y, and Chang H 2019 Adv. Electron. Mater. 5 1900552
[20] Cai L, He J, Liu Q, Yao T, Chen L, Yan W, Hu F, Jiang Y, Zhao Y, Hu T, Sun Z, and Wei S 2015 J. Am. Chem. Soc. 137 2622
[21] Guguchia Z, Kerelsky A, Edelberg D, Banerjee S, von Rohr F, Scullion D, Augustin M, Scully M, Rhodes D A, Shermadini Z, Luetkens H, Shengelaya A, Baines C, Morenzoni E, Amato A, Hone J C, Khasanov R, Billinge S J L, Santos E, Pasupathy A N, and Uemura Y J 2018 Sci. Adv. 4 eaat3672
[22] Ma Y D, Dai Y, Guo M, Niu C W, Zhu Y T, and Huang B B 2012 ACS Nano 6 1695
[23] Wang Z Y, Tang C, Sachs R, Barlas Y, and Shi J 2015 Phys. Rev. Lett. 114 016603
[24] Vinai G, Bigi C, Rajan A, Watson M D, Lee T L, Mazzola F, Modesti S, Barua S, Ciomaga H M, Balakrishnan G, King P D C, Torelli P, Rossi G, and Panaccione G 2020 Phys. Rev. B 101 035404
[25] Chua R, Zhou J, Yu X, Yu W, Gou J, Zhu R, Zhang L, Liu M, Breese M B H, Chen W, Loh K P, Feng Y P, Yang M, Huang Y L, and Wee A T S 2021 Adv. Mater. 33 2103360
[26] Yang L, Wu H, Zhang L, Zhang W, Li L, Kawakami T, Sugawara K, Sato T, Zhang G, Gao P, Muhammad Y, Wen X, Tao B, Guo F, and Chang H 2021 Adv. Funct. Mater. 31 2008116
[27] Yang L, Wu H, Zhang L, Zhang G, Li H, Jin W, Zhang W, and Chang H 2021 ACS Appl. Mater. & Interfaces 13 31880
[28] Purbawati A, Coraux J, Vogel J, Hadj-Azzem A, Wu N, Bendiab N, Jegouso D, Renard J, Marty L, Bouchiat V, Sulpice A, Aballe L, Foerster M, Genuzio F, Locatelli A, Menteş T O, Han Z V, Sun X, Núñez-Regueiro M, and Rougemaille N 2020 ACS Appl. Mater. & Interfaces 12 30702
[29] Sun X D, Li W Y, Wang X, Sui Q, Zhang T Y, Wang Z, Liu L, Li D, Feng S, and Zhong S Y 2020 Nano Res. 13 3358
[30] Wu H, Zhang W, Yang L, Wang J, Li J, Li L, Gao Y, Zhang L, Du J, Shu H, and Chang H 2021 Nat. Commun. 12 5688
[31] May A F, Ovchinnikov D, Zheng Q, Hermann R, Calder S, Huang B, Fei Z, Liu Y, Xu X, and McGuire M A 2019 ACS Nano 13 4436
[32] Seo J, Kim D Y, An E S, Kim K, Kim G Y, Hwang S Y, Kim D W, Jang B G, Kim H, Eom G, Seo S Y, Stania R, Muntwiler M, Lee J, Watanabe K, Taniguchi T, Jo Y J, Lee J, Min B I, Jo M H, Yeom H W, Choi S Y, Shim J H, and Kim J S 2020 Sci. Adv. 6 eaay8912
[33] Zhang G J, Guo F, Wu H, Wen X, Yang L, Jin W, Zhang W F, and Chang H X 2022 Nat. Commun. 13 5067
[34] Ikeda S, Miura K, Yamamoto H, Mizunuma K, Gan H D, Endo M, Kanai S, Hayakawa J, Matsukura F, and Ohno H 2010 Nat. Mater. 9 721
[35] Li X Q, Yin S Q, Liu Y P, Zhang D L, Xu X G, Miao J, and Jiang Y 2011 Appl. Phys. Express 4 043006
[36] Zhang X Q, Lu Q S, Liu W Q, Niu W, Sun J B, Cook J, Vaninger M, Miceli P F, Singh D J, Lian S W, Chang T R, He X, Du J, He L, Zhang R, Bian G, and Xu Y 2021 Nat. Commun. 12 2492
[37] Zhang G J, Wu H, Zhang L, Zhang S F, Yang L, Gao P F, Wen X K, Jin W, Guo F, Xie Y M, Li H D, Tao B, Zhang W F, and Chang H X 2022 Adv. Sci. 9 2103173
[38] Cheng R Q, Yin L, Wen Y, Zhai B X, Guo Y Z, Zhang Z F, Liao W T, Xiong W, Wang H, Yuan S, Jiang J, Liu C, and He J 2022 Nat. Commun. 13 5241
[39] Jin W, Zhang G, Wu H, Yang L, Zhang W, and Chang H 2022 arXiv:2211.06165 [cond-mat.mes-hall]
[40] Jin W, Zhang G, Wu H, Yang L, Zhang W, and Chang H 2023 Nanoscale 15 5371
[41] Yin H F, Zhang P Z, Jin W, Di B, Wu H, Zhang G, Zhang W F, and Chang H X 2023 CrystEngComm 25 1339
[42] Zhu W K, Xie S H, Lin H L, Zhang G J, Wu H, Hu T G, Wang Z, Zhang X, Xu J, Wang Y, Zheng Y, Yan F, Zhang J, Zhao L, Patanè A, Zhang J, Chang H, and Wang K 2022 Chin. Phys. Lett. 39 128501
[43] Li X L, Zhu M, Wang Y Y, Zheng F X, Dong J T, Zhou Y, You L, and Zhang J 2023 Appl. Phys. Lett. 122 082404
[44] Jin W, Zhang G, Wu H, Yang L, Zhang W, and Chang H 2023 arXiv:2303.05163 [cond-mat.mes-hall]