- Nano Review
- Open Access
Recent Advances in Two-Dimensional Spintronics
Nanoscale Research Letters volume 15, Article number: 226 (2020)
Spintronics is the most promising technology to develop alternative multi-functional, high-speed, low-energy electronic devices. Due to their unusual physical characteristics, emerging two-dimensional (2D) materials provide a new platform for exploring novel spintronic devices. Recently, 2D spintronics has made great progress in both theoretical and experimental researches. Here, the progress of 2D spintronics has been reviewed. In the last, the current challenges and future opportunities have been pointed out in this field.
With the discovery and application of the giant magnetoresistance effect (GMR), spintronics has quickly been developed into an attractive field, aiming to use the spin degree freedom of electrons as an information carrier to achieve data storage and logical operations [1,2,3]. Compared to conventional microelectronic devices based on charge, spintronic devices require less energy to switch a spin state, which can result in faster operation speed and lower energy consumption. Therefore, spintronics is the most promising technology to develop alternative multi-functional, high-speed, low-energy electronic devices. Although spin-transfer-torque magnetoresistive random-access memory (STT-MRAM) has been commercially produced, various technical issues still need to be resolved. Major challenges include the efficient generation and injection of spin-polarized carriers, long-range transmission of spin, and manipulation and detection of spin direction [4,5,6].
In parallel with the boom of spintronics, two-dimensional (2D) van der Waals (vdW) materials have been at the frontier of material research since the isolation of graphene [7,8,9]. Distinct from their bulk materials, 2D vdW materials exhibit many novel physical phenomena. Some 2D materials have already shown great potential for the engineering of next-generation 2D spintronic devices [10,11,12]. For example, graphene exhibits high electron/hole mobility, long spin lifetimes, and long diffusion lengths, which make it a promising candidate for a spin channel [13,14,15]. However, due to its characteristics of zero gap and weak spin–orbit coupling (SOC), graphene has limitations in building graphene-based current switches. In contrast, 2D transition metal dichalcogenides (TMDCs) have varied band gaps, strong SOC effect, and, especially, unique spin-valley coupling, providing a platform to manipulate spin and valley degrees of freedom for nonvolatile information storage [16, 17]. Topological insulators (TIs) with topologically protected surface states have strong spin–orbit interactions to achieve spin-momentum locking, which can suppress scattering and enhance spin and charge conversion efficiency [4, 12, 18]. Emerging 2D magnets with intrinsic magnetic ground states down to atomic-layer thicknesses open up new avenues for novel 2D spintronic applications [19,20,21].
With the development of 2D spintronics, it is necessary to review the latest experimental and theoretical work in the field. In this article, the progress of 2D spintronics has been reviewed, and some current challenges and future opportunities have also been discussed in this emerging field. The first section reviews magnetism in 2D materials, including induced magnetic moments in graphene, TIs, and some other 2D materials via the methods of doping or proximity effect, and some intrinsic 2D magnets. The second section presents the three elementary functionalities to achieve 2D spintronic device operations, including spin-charge conversion, spin transport, and spin manipulation in 2D materials and at their interfaces. The third section overviews applications of 2D spintronics. The fourth section introduces several potential 2D spintronic devices for memory storage and logic applications. The final section discusses some current challenges and future opportunities in 2D spintronics to achieve practical application.
Magnetism in 2D Materials
Magnetism has important meanings in data storage technologies. However, most 2D materials like graphene are not intrinsically magnetic. Two methods have been proposed to make nonmagnetic materials magnetic. The first method is to generate spin polarization by introducing vacancies or adding adatoms [22,23,24]. The other one is to introduce magnetism via the magnetic proximity effect with the adjacent magnetic materials [18, 25, 26]. The recently discovered 2D magnetic vdW crystals have intrinsic magnetic ground states at the atomic scale, providing unprecedented opportunities in the field of spintronics [20, 27].
Induced Magnetic Moments in Graphene
Pristine graphene is strongly diamagnetic, so a large number of theoretical and experimental studies explore the magnetism of graphene. Introducing vacancies and adding hydrogen or fluorine have been used to induce magnetic moments in graphene [23, 25, 28]. For example, Kawakami’s group utilized hydrogen adatoms to dope the graphene (Fig. 1a) and detected pure spin current by nonlocal spin transport measurement to demonstrate magnetic moment formation in graphene . As shown in Fig. 1b, the characteristic dip appearing at zero magnetic field in the nonlocal spin transport measurement shows that the pure spin current is scattered by exchange coupling between conduction electrons and local hydrogen-induced magnetic moments. In addition, graphene with fluorine adatoms and vacancy defects has paramagnetic moments, which can be measured by a SQUID (superconducting quantum interference device) . Nevertheless, the realization of long-range ferromagnetic order in doped graphene is still an overwhelming challenge. Some researchers have proposed using the magnetic proximity effect to make graphene gain magnetism . When graphene is adjacent to a magnetic insulator, the π orbitals of graphene and the neighboring spin-polarized d orbitals in the magnetic insulator have an exchange interaction to generate long-range ferromagnetic coupling. As shown in Fig. 1c, in the graphene/yttrium iron garnet (YIG) heterostructure, the measured anomalous Hall effect signal can persist to 250 K (Fig. 1d) .
Induced Magnetic Moments in TIs
2D materials are susceptible to environmental conditions, such as moisture and oxygen. The conductive surface state in TI surface regions is considered to be a more stable 2D material . In addition, the surface state of TIs exhibits the spin-momentum locking property, which provides a way to manipulate the spin signal via the charge current direction. More interestingly, breaking the time-reversal symmetry by the doping of magnetic atoms or the magnetic proximity effect can give rise to some exotic phenomena such as the quantum anomalous Hall effect (QAHE) [18, 31]. Chang et al.  first observed QAHE in Cr doped magnetic TI, Cr0.15(Bi0.1Sb0.9)1.85Te3. As demonstrated in Fig. 2a, by tuning the Fermi level of magnetically induced TI bands, we can observe a plateau of Hall conductance of e2/h. The measured results show the gate-tunable anomalous Hall resistance reaches the quantized value of h/e2 at zero magnetic field (Fig. 2b). However, the spin scattering effect of doped magnetic atoms is limited to achieve a robust long-range magnetic order at the surface of the TI. The magnetic proximity between TIs and magnetic materials can avoid the introduction of doping atoms or defects, gaining a long-range magnetic order by interfacial exchange coupling. Spin-polarized neutron reflectivity (PNR) was utilized to study the interface magnetism at the heterostructure of Bi2Se3/EuS (Fig. 2c) . The PNR result shows that the Bi2Se3/EuS bilayer has a ferromagnetic order at the interface, and this topologically enhanced interfacial ferromagnetism can persist up to room temperature (Fig. 2d). Realizing a ferromagnetic surface state in a TI is predicted to allow several prominent phenomena to emerge, such as the interfacial magnetoelectric effect  and the electric field-induced image magnetic monopole .
Induced Magnetism in Other 2D Materials
Besides graphene and TIs, magnetism induced by intrinsic defects and dopants in other 2D materials have also been investigated, including phosphorene , silicene [36, 37], GaSe , GaN , ZnO , etc. First-principles calculation results showed that an interplay between vacancy and external strain can give rise to magnetism in phosphorene. When a strain is along the zigzag direction of phosphorene and P vacancies reaches 4%, the system exhibits a spin-polarized state with a magnetic moment of ~ 1 μB per vacancy site . First-principles calculations also predicted that hole doping can induce ferromagnetic phase transition in GaSe and GaS, due to exchange splitting of electronic states at the top of the valence band. The magnetic moment can be as large as 1.0 μB per carrier [38, 39]. However, most of these investigations are limited to theoretical calculations. Further studies, particularly experimental work are needed to understand the magnetic behaviors and to explore robust 2D room temperature ferromagnetic semiconductor for practical applications.
Intrinsic 2D Magnets
Recently, another member of the 2D vdW family, the 2D magnet, has been obtained experimentally [19, 41]. This breakthrough immediately attracted extensive attention to explore the field of 2D magnetism. Xu’s group first reported that CrI3 down to the monolayer exhibits an Ising ferromagnetism with strong out-of-plane magnetic anisotropy by the magneto-optical Kerr effect (MOKE) technique (Fig. 3a) . Moreover, CrI3 exhibits a layer-dependent magnetic phase, where monolayer and trilayer CrI3 are ferromagnetic while the bilayer is antiferromagnetic. Gong et al. reported another 2D material, Cr2Ge2Te6, which has intrinsic long-range ferromagnetic order in atomic layers . Different from CrI3, Cr2Ge2Te6 is reported to be a 2D Heisenberg ferromagnet with small magnetic anisotropy. As shown in Fig. 3b, the ferromagnetic transition temperature of Cr2Ge2Te6 is related to the number of layers. Another popular 2D ferromagnet is Fe3GeTe2, which is a vdW ferromagnetic metal composed of layered Fe/FeGe/Fe, sandwiched between two Te atom layers . The anomalous Hall effect has been used to study magnetism of Fe3GeTe2, and the results show Fe3GeTe2 has strong magnetic anisotropy with an easy magnetization direction parallel to the c-axis and a Curie temperature of 230 K (Fig. 3c) . However, the Curie temperature of these materials is lower than room temperature, which is a big obstacle for devices application. Having Curie temperature above room temperature is a prerequisite for the practical application of two-dimensional magnetic materials. Researchers have prepared room temperature ferromagnetic monolayers 1 T-VSe2 by molecular beam epitaxy (MBE) . The recently reported few-layer 1 T-CrTe2 exhibited the Curie temperature as high as 316 K , which provides the possibility for the application of 2D spintronic devices in the future. In addition to 2D ferromagnetic materials, 2D antiferromagnetic materials are widely reported, such as FePS3 , MnPS3 , and CrCl3 . More surprisingly, the team of Zhang Yuanbo recently reported magnetic field-induced QAHE in an intrinsic magnetic topological insulator MnBi2Te4 . MnBi2Te4 is an antiferromagnet with intralayer ferromagnetism and interlayer antiferromagnetism. By probing quantum transport, an exact quantization of the anomalous Hall effect in a pristine five-layer MnBi2Te4 flake was observed at a moderate magnetic field of above μ0H ~ 6 T at low temperature (Fig. 3d).
Elementary Functionalities of 2D Spintronic Device Operations
Recent developments in emerging 2D materials and some advanced characterization techniques have allowed the field of 2D spintronics to develop rapidly [51,52,53]. The key issues for the realization of spintronic devices include spin-charge conversion, spin transport, and spin manipulation. The efficient generation and detection of spin current is the major challenge to developing 2D spintronic devices that replace the electrical ones. Spin transport desires a suitable transport channel with long spin lifetime and long-distance spin propagation. Spin manipulation is required to control the spin current and achieve device functionality.
Many methods are proposed to achieve spin-to-charge conversion, such as by electrical spin injection/detection or by utilizing the spin Hall effect and Edelstein effects, which originate from the SOC [54,55,56]. However, the spin Hall effect usually occurs in bulk materials, while the Edelstein effect is usually considered as an interface effect .
The “nonlocal” and “local” measurements are commonly utilized to perform electrical spin injection/detection into a channel material . For nonlocal measurement (Fig. 4a), electrode E2 is a ferromagnetic metal as a spin injector, and E3 is a ferromagnetic electrode as a spin detector. An applied current flows from electrodes E1 to E2, and E3 and E4 are used to detect the diffused pure spin current signal. The polarity of the measured voltage between E3 and E4 depends on the magnetization configurations of electrode E2 and E3. This method can gain a pure spin current without charge current, while the “local” measurements get a mixed signal of spin current and charge current (Fig. 4b). The difference of voltage between the parallel and antiparallel magnetization alignments of the electrodes E2 and E3 is considered as the signal of spin transport.
Hill et al. first reported the injection of spin into graphene by using soft magnetic NiFe electrodes . However, the spin injection efficiency is estimated to be relatively low, around 10%, which could be attributed to the conductance mismatch between ferromagnetic metal and graphene. Then, some researchers proposed using an insulating barrier such as Al2O3 or MgO as a layer to tune interfacial spin-dependent resistivity and enhance the spin injection efficiency [58,59,60], but growing a high-quality layer of oxide is a major challenge. Some methods have been used to improve the oxide layer growth technique or change to another interfacial oxide layer, such as a layer of TiO2 or HfO2 [61, 62]. However, interfacial spin-dependent resistivity is still the fundamental problem, which leads to a low spin injection efficiency. One 2D insulation material, hexagonal boron nitride (h-BN), has a crystal structure similar to that of graphene. Theoretical and experimental studies have shown that using h-BN as a tunnel barrier can produce a high-quality interface and greatly improve the spin-injection efficiency of graphene. Few-layer h-BN exhibits better spin injection performance than monolayer h-BN [63, 64]. Nevertheless, these research results still leave a big gap to be filled before practical application is possible. Ultimately, to achieve perfect (100%) spin injection requires much research, and 2D materials provide a promising direction, such as 2D heterostructures composed of 2D ferromagnetic materials, 2D tunnel barriers, and 2D transport channels.
The (inverse) Rashba–Edelstein effect is an interface effect originating from the strong SOC, which can be utilized to achieve spin-charge conversion . Although intrinsic graphene has a rather weak SOC, it can achieve efficient spin-charge conversion by using the strong SOC of adjacent material via proximity effect [66, 67]. As shown in Fig. 4c, when graphene is adjacent to the ferromagnetic insulator YIG, the spin current is generated in the YIG layer via spin pumping, then converted to a charge current in graphene by the inverse Edelstein effect . Figure 4d shows the spin pumping voltage curves as a function of the field in the YIG/graphene device. The spin pumping voltages can be detected in the magnetic field perpendicular to the graphene channel. Moreover, when the external magnetic field is turned along the graphene channel, there is no spin pumping voltage. Furthermore, an ionic liquid gating applied on the graphene surface can obviously modulate the properties of graphene to change the spin-to-charge conversion efficiency of YIG/graphene .
Unlike graphene, TMDCs with strong SOC are considered to be promising materials for achieving spin-charge conversion [69, 70]. A large spin–orbit torque (SOT) in monolayer TMDC (MoS2 or WSe2)/CoFeB bilayer structure was generated via current-induced spin accumulation caused by the Rashba–Edelstein effect (Fig. 4e, f) . The field-like torque and damping-like torque were determined via a second-harmonic measurement, and the results show that large-area monolayer TMDCs have potential applications because of their high efficiency for magnetization reversal. In addition, the technique of spin-torque ferromagnetic resonance (ST-FMR) has been used to investigate the spin and charge conversion in TMDCs. For example, an interesting ST-FMR result shows the SOT can be controlled through the crystal symmetry of WTe2 in WTe2/ Permalloy bilayers. When current is applied along the low-symmetry axis of WTe2, an out-of-plane anti-damping torque can be generated . The spin-momentum locking property in TI surface states is useful to achieve spin current injection into adjacent materials via SOT. Due to the strong correlation between the spin polarization direction and charge current direction, the spin direction can be manipulated by the charge current in the TIs. Different measurement techniques have been used to investigate the spin-charge conversion, including second harmonic measurement, spin pumping, and ST-FMR. These measurement results demonstrate that it is possible to generate efficient SOT in 2D materials such as TMDCs and TIs.
The key to spin transport is to get a favorable spin transport channel with a long spin diffusion length and spin relaxation time. Spin relaxation is caused by momentum scattering, so graphene with weak SOC is regarded as an ideal material for spin transport [14, 73]. Tombros et al.  realized electronic spin transport and spin precession in a lateral single graphene spin valve at room temperature by nonlocal measurement in 2007. As shown in Fig. 5a, b, the nonlocal spin valve is composed of four-terminal ferromagnetic cobalt as electrodes, a thin Al2O3 oxide layer as a barrier, and a graphene sheet as the spin transport channel. The measurement signal in Fig. 5c shows that if the ferromagnetic electrodes for spin injection and spin detection have parallel magnetizations, the nonlocal resistance measured by contacts 1 and 2 has a positive value. If the ferromagnetic electrodes for spin injection and spin detection have antiparallel magnetizations, then the nonlocal resistance shows a negative value. The Hanle spin precession can be used to determine spin diffusion length and spin lifetime. As shown in Fig. 5d, the spin lifetime (τsf) and spin relaxation length (λsf) are 125 ps and 1.3 μm, respectively, in a lateral single graphene spin valve at room temperature. Furthermore, the gate can be used to enhance the spin relaxation length and spin life [75, 76]. Theory predicted that the spin lifetime in pristine graphene can reach 1 μs, whereas the reported experiment values range from picoseconds to a few nanoseconds.
Many improved methods are used to increase spin diffusion length and spin life, and some devices already exhibit long spin diffusion lengths in the micrometer range [13, 77, 78]. For example, graphene epitaxially grown on SiC has high mobility, exhibiting spin transport efficiency up to 75% and spin diffusion length exceeding 100 µm . The h-BN/graphene/h-BN heterostructure exhibits a long-distance spin transport performance, where the spin diffusion length can reach 30.5 μm at room temperature . Spin transport in 2D materials can be affected by diffusion/drift, which can be modulated by applying an electrical field. Ingla-Aynés et al.  reported a spin relaxation length up to 90 μm in h-BN encapsulated bilayer graphene by using carrier drift. However, the weak SOC and zero bandgap in intrinsic graphene restrict its prospects for semiconducting spin devices. Black phosphorus has a sizeable direct bandgap and room-temperature mobility of 1000 cm2 V−1 s−1, which make it an ideal semiconducting spintronic material [81,82,83]. Avsar et al.  constructed a lateral spin valve based on an ultrathin black phosphorus sheet and measured its spin transport properties at room temperature via the nonlocal geometry (Fig. 5e, f). The electronic spin transport in Fig. 5g shows that as the magnetization directions of the ferromagnets switch, the nonlocal resistance has a change of ΔR ≈ 15Ω. In addition to this, the Hanle spin precession shows spin relaxation times up to 4 ns and spin relaxation lengths exceeding 6 µm (Fig. 5h). The spin transport in black phosphorus is closely related to the charge carrier concentration, so the spin signal can be controlled by applying an electric field.
Realizing the manipulation of spin is the key to effective device functionalization. Applying a gate voltage can control the carrier concentration in the material, which can be used to manipulate the spin signals [85, 86]. Various 2D materials as spin transport channels have been investigated to realize the adjustment of the spin transport parameters via applying a gate voltage. For example, bias induced graphene can get a spin-injection and detection polarization up to 100% in ferromagnet/bilayer h-BN/graphene/h-BN heterostructure . A gate-tunable spin valve based on black phosphorus can reach a spin relaxation time in the nanosecond range and a long spin relaxation length . For a semiconducting MoS2 channel, applying a gate voltage can still get a relatively long spin-diffusion length, larger than 200 nm . However, a suitable spin field-effect device requires a clear switching ratio, which is a challenge for graphene and even for semiconducting 2D materials [87, 88].
To solve this issue, a vdW heterostructure based on atomically thin graphene and semiconducting MoS2 has been developed to achieve a spin field-effect switch via applying a gate voltage (Fig. 6a) . In this structure, the superior spin transport properties of graphene and the strong SOC of MoS2 are combined. The applied gate voltage can change the conductivity of MoS2 and spin absorption during the spin transport, which results in switching of the spin current between ON and OFF states in the graphene channel (Fig. 6b). Another research effort produced a similar report about the graphene/MoS2 vdW heterostructure. In this report, an electric gate control of the spin current and spin lifetime in the graphene/MoS2 heterostructure was achieved at room temperature . Moreover, that report pointed out that the mechanism of gate tunable spin parameters stemmed from gate tuning of the Schottky barrier at the MoS2/graphene interface and MoS2 channel conductivity.
Current-induced SOT is regarded as another efficient strategy to manipulate spin. The spin current, generated by the spin Hall effect within the heavy metals or the Rashba effect at the interfaces, can exert a spin torque to ferromagnets and thereby realize magnetization switching [91,92,93]. Efficient current-induced magnetization switching via SOT may lead to innovative spintronic applications. Due to strong SOC and time-inversion symmetry breaking, magnetically doped TIs are being considered as a promising material to manipulate spin signals via SOT . Wang’s group first experimentally demonstrated a magnetization switching induced by an in-plane current in an epitaxial Cr-doped TI (Bi0.5Sb0.5)2Te3/(Cr0.08Bi0.54Sb0.38)2Te3 bilayer film (Fig. 6c) . The spin Hall angle in the Cr-doped TI film, ranging from 140 to 425, is almost three orders of magnitude larger than that in heavy metal/ferromagnetic heterostructures, and the critical switching current density is below 8.9 × 104 A cm−2 at 1.9 K (Fig. 6d). Furthermore, this team also reported an effective electric field control of SOT in a Cr-doped (Bi0.5Sb0.42)2Te3 thin film epitaxially grown on GaAs substrate (Fig. 6e) . The gate effect on the magnetization switching was investigated by scanning gate voltage under a constant current and an applied in-plane magnetic field in the film (Fig. 6f). The SOT intensity depends strongly on the spin-polarized surface current in the thin film, and it can be modulated within a suitable gate voltage range. The effective electric field control of SOT in the TI-based magnetic structures has potential applications in magnetic memory and logic devices.
In addition, electrical control of emerged 2D magnets has also been investigated. For example, utilizing electric fields or electrostatic doping can achieve the magnetic conversion of bilayer CrI3 antiferromagnetic to ferromagnetic . The coercivity and saturation field of few-layer Cr2Ge2Te6 can be modulated via ionic liquid gating . In contrast to magnetic semiconductor, electrostatic doping can be used to control the carrier concentrations of the ferromagnetic metal, and the ferromagnetic transition temperature of Fe3GeTe2 can be dramatically raised to room temperature via an ionic gate . The emergence and research of 2D magnets provide a new platform for engineering next-generation 2D spintronic devices.
Applications of 2D Spintronics
2D materials exhibit great potential for the engineering of next-generation 2D spintronic devices. Graphene with high electron/hole mobility, long spin lifetimes, and long diffusion lengths is a promising candidate for a spin channel. Moreover, graphene can gain magnetism by introducing adatoms, or magnetic proximity effect [23, 25]. The carrier density in proximity-induced ferromagnetic graphene can be modulated by gating, allowing to observe Fermi energy dependence of the anomalous Hall effect conductivity. This result can help understand the physical origin of anomalous Hall effect in 2D Dirac fermion systems. Realizing a ferromagnetic surface state in a TI is predicted to allow several prominent phenomena to emerge, such as the interfacial magnetoelectric effect , and the electric field-induced image magnetic monopole . However, the current technology of inducing magnetism in TI is confined to low temperatures, which restrict its potential for applications. A key requirement for useful applications is the generation of room temperature ferromagnetism in the TI. The PNR result shows that the Bi2Se3/EuS bilayer has a ferromagnetic order at the interface, and this topologically enhanced interfacial ferromagnetism can persist up to room temperature . The topological magnetoelectric response in such an engineered TI could allow efficient manipulation of the magnetization dynamics by an electric field, providing an energy-efficient topological control mechanism for future spin-based technologies.
The STT, and tunnel magnetoresistance (TMR) effects offer alternative approaches for write and read-out operations. The STT effect refers to the reorientation of the magnetization of ferromagnetic materials via the transfer of spin angular momenta. Efficient current-induced magnetization switching via SOT may lead to innovative spintronic applications [71, 100]. Due to strong SOC and time-inversion symmetry breaking, magnetically doped TIs are being considered as a promising material to manipulate spin signals via SOT . TMR refers to magnetization-dependent magnetoresistance behavior. A high TMR ratio is the key to achieve spintronic devices with higher sensitivity, lower energy consumption. 2D materials with high-quality crystal and sharp interfaces can achieve some new functionalities such as spin filtering. The 2D vdW MTJ consists of a 2D magnetic CrI3 layer as a spin filtering tunnel barrier, which reaches a value of TMR up 19,000% . Progress in the fabrication of graphene-based and other 2D heterostructures has led to the optimization of long-distance spin diffusion (up to tens of micrometres), as well as directional guiding of the spin current [13, 64]. Spin manipulation, electrical gating , electrical field induced drift , SOT-induced switching [95, 96], and the magnetic proximity effect [25, 32] have been explored to develop next-generation MRAM.
2D Spintronic Devices for Memory Storage and Logic Applications
Great efforts have been made to search for new 2D spintronic devices. According to the function, 2D spintronic devices can be classified as memory storage or logic devices. Here we focus on several important 2D spintronic devices, including the 2D magnetic tunnel junction (MTJ), 2D spin field-effect transistor (sFET), and 2D spin logic gate.
The discovery of the GMR opens the door for 2D spintronics. However, TMR has a stronger magnetoresistance ratio than GMR, so TMR holds greater potential in magnetic storage applications. The TMR structure consists of two ferromagnetic layers and an intermediate insulating layer, which is called the MTJ. The tunneling probability is related to the density of states near the Fermi energy in the ferromagnetic layers. When the two magnetic layers are parallel, the similar density of states for each spin-state can provide more available states for tunneling, resulting in a low resistance state. On the other hand, when the layers are antiparallel, a mismatch between spin channels of the source and sink will result in a high resistance state. Some issues in traditional thin-film MTJs limit the achievement of a high TMR ratio, such as the quality of the insulation barrier and the thermal stability . 2D materials with high-quality crystal and sharp interfaces may offer promising routes to address these issues and even achieve some new functionalities such as spin filtering.
Karpan et al. first explored graphene layers as the barrier in vertical MTJ by computational means in 2007 . They proposed a match between the band structure of graphene and that of nickel, predicting a large spin polarization close to 100%, which can result in a large TMR up to 500%. However, the subsequent experimental results show that the MTJs based on graphene exhibit a very low TMR. Compared to monolayer or bilayer graphene, the few-layer MTJ holds the highest recorded TMR signal of up to 31% in graphene-based MTJs [11, 15]. In addition to graphene, some other 2D materials have been explored as tunneling barrier layers, including insulating h-BN and semiconducting TMDCs [104, 105]. Piquemal-Banci et al.  fabricated Fe/h-BN/Co junctions where the h-BN monolayer was directly grown on Fe by using the chemical vapor deposition (CVD) method, observing large spin signals of TMR and the spin polarization of P ~ 17%. MTJs based on MoS2 or WSe2 were reported to have only a few percent of the TMR signal; further exploration is needed to achieve a high TMR ratio.
Emerging 2D magnetic materials exhibit many surprising properties. When the magnetizations in bilayer CrI3 are switched to different magnetic configurations (Fig. 7a), the MTJ based on CrI3 exhibits a giant TMR produced by the spin-filtering effect [101, 106, 107]. As demonstrated in Fig. 7b, the 2D vdW MTJ consists of a 2D magnetic CrI3 layer as a spin filtering tunnel barrier, graphene as a contact electrode, and h-BN as an encapsulation layer to prevent device degradation. The transport result shows that the TMR is enhanced as the CrI3 layer thickness increases, and it reaches a value of 19,000% in four-layer CrI3 based MTJ at low temperature (Fig. 7c) . Subsequently, Xu’s group also reported gate-tunable TMR in a dual-gated MTJ structure based on four-layer CrI3. The TMR can be modulated from 17,000 to 57,000% by varying the gate voltages in a fixed magnetic field [108, 109]. Moreover, with few-layer Fe3GeTe2 serving as ferromagnetic electrodes, the TMR in Fe3GeTe2/h-BN/Fe3GeTe2 heterostructures can reach 160% at low temperature . More interestingly, Zhou et al. reported a theoretical investigation of a VSe2/MoS2/VSe2 heterojunction, where the VSe2 monolayer acts as a room-temperature ferromagnet, and the large TMR can reach 846% at 300 K . On the other hand, the strong spin Hall conductivity of MoS2 holds potential to switch the magnetization of the VSe2 free layer by SOT. Therefore, they put forward the concept of SOT vdW MTJ with faster reading and writing operations, which offers new opportunities for 2D spintronic devices.
Datta and Das first proposed the idea of the sFET in 1990 . The sFET consists of the source and sink ferromagnetic electrodes, and a two-dimensional electron gas (2DEG) channel which can be controlled by an electrical gate. The gate voltage can result in a spin precession and, consequently, a change in the spin polarization of the current on the channel. Since switching the current through the device requires only little energy and a short time, sFET is expected to be a 2D spintronic device with low power consumption and high computing speed.
As mentioned in the previous section, graphene with high carrier concentration and weak SOC is considered to be a promising candidate as a spin transport channel . Michetti et al.  designed a double-gate field-effect transistor structure, where bilayer graphene acts as the transport channel. Theoretical analysis shows that the spin precession of carriers in the graphene channel can be turned on and off by the application of a differential gate voltage. Experimentally, Avsar et al. first reported a dual-gated bilayer graphene structure with h-BN as a dielectric layer, where the spin current propagation in bilayer graphene channel can be controlled by exerting a vertical electric field . The transport results show that the spin-relaxation time decreases monotonically as the carrier concentration increases, and the spin signal exhibits a rapid decrease, eventually becoming undetectable close to the charge neutrality point. A suitable spin field-effect device requires a clear switching ratio, which is a challenge for graphene.
To solve this issue, a graphene/MoS2 heterostructure has been developed to achieve a spin field-effect switch via applying a gate voltage. Two independent groups demonstrated that the applied gate voltage can change the conductivity of MoS2 and result in spin absorption during the spin transport, which gives rise to switching the spin current between ON and OFF states in the graphene channel . Due to the low spin injection efficiency and rapid spin relaxation in channels, it is a challenge to achieve a large high-to-low conductance ratio in 2D sFET device. However, the discovery of 2D magnetic crystals provides new opportunities to explore new 2D spintronic devices. Kin Fai Mak’s group reported a spin tunnel field-effect transistor (sTFET) based on a dual-gated graphene/CrI3/graphene heterostructure . By using bilayer CrI3 as a magnetic tunnel barrier, the applied gate voltage can switch magnetization configurations of bilayer CrI3 from interlayer antiferromagnetic to ferromagnetic states under a constant magnetic field near the spin-flip transition. Distinct from conventional spin transistors, these devices rely on electrically controlling the magnetization configuration switching rather than the signal of spin current in the channel. This technique allows the sTFET devices to achieve a large high–low conductance ratio approaching 400%, which provides a new approach for exploring memory applications.
2D Spin Logic Gate
Dery and Sham first reported a spin logic device based on an “exclusive or” (XOR) gate . The XOR logic gate structure includes a semiconductor channel and three ferromagnetic terminals. An XOR logic operation can be implemented by different spin accumulations, which is caused by different magnetization configurations of the input terminals . Experimentally, the proposed three-terminal XOR logic gate achieved logical operations in a graphene spintronic device at room temperature [117,118,119]. As shown in Fig. 7c, the device includes single-layer graphene as the channel, and three ferromagnetic terminals composed of A, B, and M Co electrodes with MgO tunnel barriers. The magnetization of the electrodes A and B represents the input states 0 or 1, and the current of the electrode M acts as the output state. The magnetizations of input electrodes A and B will be switched by varying an applied external magnetic field, which results in a different spin accumulation in the M electrode, corresponding to a different output current. If the input A and B electrodes have identical contributions to the output M electrode, then the current in the output ferromagnetic terminal has a detectable value only when the magnetization of input ferromagnetic terminals are antiparallel (01 or 10). When the magnetizations of the input ferromagnetic terminals are parallel (00 or 11), the output current is almost zero. Therefore, the XOR logic operation can be achieved (Fig. 7d).
Dery et al. further designed a reconfigurable magnetologic gate with five-terminal structure combining two XOR gates-XOR (A, X) and XOR (B, Y) with a shared output terminal, M . Similar to the three-terminal XOR logic gate, the different magnetic configurations of input electrodes give rise to the different spin accumulation in the output terminal M, which results in different output signals. By analogy, a finite number of these XOR gates can be used to implement any binary logic function. Subsequently, other groups extended this theoretical design to experimental studies by constructing graphene spin logic gates [120,121,122]. Various modeling, simulation, and experimental explorations of 2D spin logic gates have helped to accelerate the progress toward building practical spin logic applications. However, two key issues remain in the research of graphene spin logic gates. The first one is to balance the contributions of two input terminals to the output one. The other one is to eliminate the influence of background signals on the output.
Challenges and Opportunities in 2D Spintronics
As discussed above, much theoretical and experimental research has been carried out to explore spintronics based on 2D materials, and considerable progress has been achieved [15, 123, 124]. However, great challenges still need to be addressed for the practical application of 2D memory and logic applications. We now discuss three of these: physical mechanisms, materials science, and device engineering.
Due to the complexity of the experiments, the proposed theoretical research and experimental results usually have large discrepancies. For example, based on the mechanism of spin relaxation, theory predicted that the spin lifetime for pristine graphene would be up to 1 μs, whereas experimental values range from tens of picoseconds to a few nanoseconds [14, 57, 103]. Furthermore, the spin injection efficiency of graphene measured experimentally ranges from a few percent to 10%, which is far smaller than the theoretical prediction value of 60–80% . These differences indicate that more in-depth physical mechanisms and accurate theoretical models need to be proposed and developed to better guide the research direction and analyze the experimental results.
2D materials provide an ideal platform to construct various heterostructures for spintronic applications. However, there are still many major problems in 2D materials. For example, stability is a great challenge for 2D materials. Most 2D materials of thickness close to the atomic level are susceptible to moisture, oxygenation, and temperature, especially the recently emerging 2D magnetic materials, which must be peeled off in a glove box with ultra-low water and oxygen content. Besides this, most currently available 2D magnets rely on mechanical exfoliation, and their low magnetic transition temperature is far below room temperature. These are significant limitations because stability in air, convenient wafer-scale synthesis, and operation above room temperature are prerequisites for 2D materials used in practical applications.
Breakthroughs have been made in the fundamental study of 2D spintronics, such as enhanced spin injection efficiency by using 2D tunnel barriers h-BN, long spin diffusion length up to 30 μm at room temperature in graphene-based 2D heterostructures , and high TMR up to 19,000% by using 2D magnets as spin filter barriers . Based on the study of 2D spintronic devices, it is promising to develop the low-power device applications, including advanced magnetic memories and spin logic circuits, which are compatible with the existing complementary metal-oxide semiconductor (CMOS) electronics. However, the design and application of functional 2D spintronic devices are still in the early theoretical prediction and proof-of-concept stage.
2D spintronics is an important scientific research field with many potential applications for future technologies. As mentioned above, considerable challenges currently remain, but there are also many opportunities. Spin valves based on graphene as the spin transport channel can exhibit a long spin diffusion length up to 30 mm at room temperature . Magnetic tunnel junctions with four-layer CrI3 as spin filter tunneling barriers show giant TMR up to 19,000% at low temperatures . The magnetic transition temperature of Fe3GeTe2 can reach above room temperature via an ionic liquid gate or when tailored by a TI [99, 126]. Spin-polarized current can be injected from WTe2 into magnetic substrates by SOT switching . New concepts of spin tunneling field-effect transistors based on 2D magnets CrI3 have been proposed as well. The demonstration of giant TMR, the efficient voltage control of 2D magnetism, and the magnetization switching in 2D magnets by STT or SOT all open up opportunities for potential next-generation spintronic devices based on atomically thin vdW crystals [21, 100].
The study about the magnetic properties of 2D materials is of great significance to the development of 2D spintronics. The magnetic interaction in graphene and TIs has scarcely been explored, and recently discovered 2D magnets also provide an ideal platform to study 2D magnetism. Great progress has been made in 2D spintronics in recent decades, especially in graphene spintronics. However, the origin of spin relaxation in graphene is still a major open question, and further improvement in the spin lifetime and spin diffusion length remains an important research direction for graphene-based spintronic devices. The practical application of 2D spintronic devices still requires meeting great challenges, including related physical mechanisms, materials science, and device engineering. The development of technology, the improvement of theoretical models, and the exploration of new materials all provide more opportunities for new-generation 2D spintronic device applications in the future.
Availability of data and materials
Giant magnetoresistance effect
Spin-transfer-torque magnetoresistive random-access memory
Van der Waals
Transition metal dichalcogenides
Superconducting quantum interference device
Yttrium iron garnet
Quantum anomalous Hall effect
Spin-polarized neutron reflectivity
Magneto-optical Kerr effect
Molecular beam epitaxy
Hexagonal boron nitride
Spin-torque ferromagnetic resonance
Magnetic tunnel junction
Spin field-effect transistor
Chemical vapor deposition
Two-dimensional electron gas
Spin tunnel field-effect transistor
Complementary metal-oxide semiconductor
Utic IZ, Fabian J, Sarma SD (2004) Spintronics: fundamentals and applications. Rev Mod Phys 76:323–386
Sinova J, Zutic I (2012) New moves of the spintronics tango. Nat Mater 11(5):368–371
Wolf SA, Awschalom DD, Buhrman RA, Daughton JM, Sv M, Roukes ML, Chtchelkanova AY, Treger DM (2001) Spintronics: a spin-based electronics vision for the future. Science 294:1488–1495
Šmejkal L, Mokrousov Y, Yan B, MacDonald AH (2018) Topological antiferromagnetic spintronics. Nat Phys 14(3):242–251
Linder J, Robinson JWA (2015) Superconducting spintronics. Nat Phys 11(4):307–315
Jungwirth T, Marti X, Wadley P, Wunderlich J (2016) Antiferromagnetic spintronics. Nat Nanotechnol 11(3):231–241
Liu Y, Huang Y, Duan X (2019) Van der Waals integration before and beyond two-dimensional materials. Nature 567(7748):323–333
Liu Y, Weiss NO, Duan X, Cheng H-C, Huang Y, Duan X (2016) Van der Waals heterostructures and devices. Nat Rev Mater 1(9):1–17
Novoselov KS, Mishchenko A, Carvalho A, Castro Neto AH (2016) 2D materials and van der Waals heterostructures. Science 353(6298):aac9439
Liu C, Chen H, Wang S, Liu Q, Jiang YG, Zhang DW, Liu M, Zhou P (2020) Two-dimensional materials for next-generation computing technologies. Nat Nanotechnol 15(7):545–557
Han W (2016) Perspectives for spintronics in 2D materials. APL Mater 4(3):032401
Pesin D, MacDonald AH (2012) Spintronics and pseudospintronics in graphene and topological insulators. Nat Mater 11(5):409–416
Drogeler M, Franzen C, Volmer F, Pohlmann T, Banszerus L, Wolter M, Watanabe K, Taniguchi T, Stampfer C, Beschoten B (2016) Spin lifetimes exceeding 12 ns in graphene nonlocal spin valve devices. Nano Lett 16(6):3533–3539
Han W, Kawakami RK, Gmitra M, Fabian J (2014) Graphene spintronics. Nat Nanotechnol 9(10):794–807
Roche S, Åkerman J, Beschoten B, Charlier J-C, Chshiev M, Prasad Dash S, Dlubak B, Fabian J, Fert A, Guimarães M, Guinea F, Grigorieva I, Schönenberger C, Seneor P, Stampfer C, Valenzuela SO, Waintal X, van Wees B (2015) Graphene spintronics: the European flagship perspective. 2D Mater 2(3):030202
Manzeli S, Ovchinnikov D, Pasquier D, Yazyev OV, Kis A (2017) 2D transition metal dichalcogenides. Nat Rev Mater 2(8):17033
Wang Z, Ki DK, Chen H, Berger H, MacDonald AH, Morpurgo AF (2015) Strong interface-induced spin-orbit interaction in graphene on WS2. Nat Commun 6:8339
Wei P, Katmis F, Assaf BA, Steinberg H, Jarillo-Herrero P, Heiman D, Moodera JS (2013) Exchange-coupling-induced symmetry breaking in topological insulators. Phys Rev Lett 110(18):186807
Li H, Ruan S, Zeng YJ (2019) Intrinsic van der Waals magnetic materials from bulk to the 2D limit: new frontiers of spintronics. Adv Mater 31(27):1900065
Gong C, Zhang X (2019) Two-dimensional magnetic crystals and emergent heterostructure devices. Science 363:705
Gibertini M, Koperski M, Morpurgo AF, Novoselov KS (2019) Magnetic 2D materials and heterostructures. Nat Nanotechnol 14(5):408–419
Wang Y, Huang Y, Song Y, Zhang X, Ma Y, Liang J, Chen Y (2008) Room-temperature ferromagnetism of graphene. Nano Lett 9:220–224
McCreary KM, Swartz AG, Han W, Fabian J, Kawakami RK (2012) Magnetic moment formation in graphene detected by scattering of pure spin currents. Phys Rev Lett 109(18):186604
Chang C-Z, Zhang J, Feng X, Shen J, Zhang Z, Guo M, Li K, Ou Y, Wei P, Wang L-L, Ji Z-Q, Feng Y, Ji S, Chen X, Jia J, Dai X, Fang Z, Zhang S-C, He K, Wang Y, Lu L, Ma X-C, Xue Q-K (2013) Experimental observation of the quantum anomalous hall effect in a magnetic topological insulator. Science 340:167–170
Wang Z, Tang C, Sachs R, Barlas Y, Shi J (2015) Proximity-induced ferromagnetism in graphene revealed by the anomalous Hall effect. Phys Rev Lett 114(1):016603
Tang C, Zhang Z, Lai S, Tan Q, Gao WB (2020) Magnetic proximity effect in graphene/CrBr3 van der Waals heterostructures. Adv Mater 32(16):e1908498
Zhong D, Seyler KL, Lin P, Cheng R, Sivadas N, Huang B, Schmidgall E, Taniguchi T, Watanabe K, McGuire MA, Wang Y, Xiao D, Fu K-C, Xu X (2017) Van der Waals engineering of ferromagnetic semiconductor heterostructures for spin and valleytronics. Sci Adv 3:e1603113
Nair RR, Sepioni M, Tsai IL, Lehtinen O, Keinonen J, Krasheninnikov AV, Thomson T, Geim AK, Grigorieva IV (2012) Spin-half paramagnetism in graphene induced by point defects. Nat Phys 8(3):199–202
Hallal A, Ibrahim F, Yang H, Roche S, Chshiev M (2017) Tailoring magnetic insulator proximity effects in graphene: first-principles calculations. 2D Mater 4(2):025074
Jiang J, Xiao D, Wang F, Shin JH, Andreoli D, Zhang J, Xiao R, Zhao YF, Kayyalha M, Zhang L, Wang K, Zang J, Liu C, Samarth N, Chan MHW, Chang CZ (2020) Concurrence of quantum anomalous Hall and topological Hall effects in magnetic topological insulator sandwich heterostructures. Nat Mater 19(7):732–737
Kou X, Guo ST, Fan Y, Pan L, Lang M, Jiang Y, Shao Q, Nie T, Murata K, Tang J, Wang Y, He L, Lee TK, Lee WL, Wang KL (2014) Scale-invariant quantum anomalous Hall effect in magnetic topological insulators beyond the two-dimensional limit. Phys Rev Lett 113(13):137201
Katmis F, Lauter V, Nogueira FS, Assaf BA, Jamer ME, Wei P, Satpati B, Freeland JW, Eremin I, Heiman D, Jarillo-Herrero P, Moodera JS (2016) A high-temperature ferromagnetic topological insulating phase by proximity coupling. Nature 533(7604):513–516
Essin AM, Moore JE, Vanderbilt D (2009) Magnetoelectric polarizability and axion electrodynamics in crystalline insulators. Phys Rev Lett 102(14):146805
Hasan MZ, Kane CL (2010) Colloquium: topological insulators. Rev Mod Phys 82(4):3045–3067
Chintalapati S, Shen L, Xiong Q, Feng YP (2015) Magnetism in phosphorene: interplay between vacancy and strain. Appl Phys Lett 107(7):072401
Zhao YC, Ni J (2014) Spin-semiconducting properties in silicene nanoribbons. Phys Chem Chem Phys 16(29):15477–15482
Zheng F-B, Zhang C-W, Yan S-S, Li F (2013) Novel electronic and magnetic properties in N or B doped silicene nanoribbons. J Mater Chem C 1(15):2735
Cao T, Li Z, Louie SG (2015) Tunable magnetism and half-metallicity in hole-doped monolayer GaSe. Phys Rev Lett 114(23):236602
Ao L, Xiao HY, Xiang X, Li S, Liu KZ, Huang H, Zu XT (2015) Functionalization of a GaSe monolayer by vacancy and chemical element doping. Phys Chem Chem Phys 17(16):10737–10748
Ren J, Zhang H, Cheng X (2013) Electronic and magnetic properties of all 3d transition-metal-doped ZnO monolayers. Int J Quantum Chem 113(19):2243–2250
Bonilla M, Kolekar S, Ma Y, Diaz HC, Kalappattil V, Das R, Eggers T, Gutierrez HR, Phan MH, Batzill M (2018) Strong room-temperature ferromagnetism in VSe2 monolayers on van der Waals substrates. Nat Nanotechnol 13(4):289–293
Huang B, Clark G, Navarro-Moratalla E, Klein DR, Cheng R, Seyler KL, Zhong D, Schmidgall E, McGuire MA, Cobden DH, Yao W, Xiao D, Jarillo-Herrero P, Xu X (2017) Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit. Nature 546(7657):270–273
Gong C, Li L, Li Z, Ji H, Stern A, Xia Y, Cao T, Bao W, Wang C, Wang Y, Qiu ZQ, Cava RJ, Louie SG, Xia J, Zhang X (2017) Discovery of intrinsic ferromagnetism in two-dimensional van der Waals crystals. Nature 546(7657):265–269
Fei Z, Huang B, Malinowski P, Wang W, Song T, Sanchez J, Yao W, Xiao D, Zhu X, May AF, Wu W, Cobden DH, Chu JH, Xu X (2018) Two-dimensional itinerant ferromagnetism in atomically thin Fe3GeTe2. Nat Mater 17(9):778–782
Tan C, Lee J, Jung SG, Park T, Albarakati S, Partridge J, Field MR, McCulloch DG, Wang L, Lee C (2018) Hard magnetic properties in nanoflake van der Waals Fe3GeTe2. Nat Commun 9(1):1554
Sun X, Li W, Wang X, Sui Q, Zhang T, Wang Z, Liu L, Li D, Feng S, Zhong S, Wang H, Bouchiat V, Regueiro MN, Rougemaille N, Coraux J, Wang Z, Dong B, Wu X, Yang T, Yu G, Wang B, Han ZV, Han X, Zhang Z Room temperature 2D ferromagnetism in few-layered 1T-CrTe2. arXiv:1909.09797v1
Lee JU, Lee S, Ryoo JH, Kang S, Kim TY, Kim P, Park CH, Park JG, Cheong H (2016) Ising-type magnetic ordering in atomically thin FePS3. Nano Lett 16(12):7433–7438
Kim K, Lim SY, Kim J, Lee J-U, Lee S, Kim P, Park K, Son S, Park C-H, Park J-G, Cheong H (2019) Antiferromagnetic ordering in van der Waals 2D magnetic material MnPS3 probed by Raman spectroscopy. 2D Mater 6(4):041001
Cai X, Song T, Wilson NP, Clark G, He M, Zhang X, Taniguchi T, Watanabe K, Yao W, Xiao D, McGuire MA, Cobden DH, Xu X (2019) Atomically thin CrCl3: an in-plane layered antiferromagnetic insulator. Nano Lett 19(6):3993–3998
Deng Y, Yu Y, Shi MZ, Guo Z, Xu Z, Wang J, Chen XH, Zhang Y (2020) Quantum anomalous Hall effect in intrinsic magnetic topological insulator MnBi2Te4. Science 367:895–900
Lin X, Yang W, Wang KL, Zhao W (2019) Two-dimensional spintronics for low-power electronics. Nat Electron 2(7):274–283
Choudhuri I, Bhauriyal P, Pathak B (2019) Recent advances in graphene-like 2D materials for spintronics applications. Chem Mater 31(20):8260–8285
Wang X, Parkin S, Xue Q-K (2016) Preface to special topic: 2D spintronics. APL Mater 4(3):032201
Tsai WF, Huang CY, Chang TR, Lin H, Jeng HT, Bansil A (2013) Gated silicene as a tunable source of nearly 100% spin-polarized electrons. Nat Commun 4:1500
Han W, Otani Y, Maekawa S (2018) Quantum materials for spin and charge conversion. NPJ Quantum Mater 3(1):1–16
Dushenko S, Ago H, Kawahara K, Tsuda T, Kuwabata S, Takenobu T, Shinjo T, Ando Y, Shiraishi M (2016) Gate-tunable spin-charge conversion and the role of spin-orbit interaction in graphene. Phys Rev Lett 116(16):166102
Hill EW, Geim AK, Novoselov K, Schedin F, Blake P (2006) Graphene spin valve devices. IEEE Trans Magn 42(10):2694–2696
Dash SP, Sharma S, Patel RS, de Jong MP, Jansen R (2009) Electrical creation of spin polarization in silicon at room temperature. Nature 462(7272):491–494
Jiang X, Wang R, Shelby RM, Macfarlane RM, Bank SR, Harris JS, Parkin SS (2005) Highly spin-polarized room-temperature tunnel injector for semiconductor spintronics using MgO(100). Phys Rev Lett 94(5):056601
Lou X, Adelmann C, Crooker SA, Garlid ES, Zhang J, Reddy KSM, Flexner SD, Palmstrøm CJ, Crowell PA (2007) Electrical detection of spin transport in lateral ferromagnet–semiconductor devices. Nat Phys 3(3):197–202
Han W, Pi K, McCreary KM, Li Y, Wong JJ, Swartz AG, Kawakami RK (2010) Tunneling spin injection into single layer graphene. Phys Rev Lett 105(16):167202
Zou K, Hong X, Keefer D, Zhu J (2010) Deposition of high-quality HfO2 on graphene and the effect of remote oxide phonon scattering. Phys Rev Lett 105(12):126601
Piquemal-Banci M, Galceran R, Caneva S, Martin MB, Weatherup RS, Kidambi PR, Bouzehouane K, Xavier S, Anane A, Petroff F, Fert A, Robertson J, Hofmann S, Dlubak B, Seneor P (2016) Magnetic tunnel junctions with monolayer hexagonal boron nitride tunnel barriers. Appl Phys Lett 108(10):102404
Gurram M, Omar S, Wees BJV (2017) Bias induced up to 100% spin-injection and detection polarizations in ferromagnet/bilayer-hBN/graphene/hBN heterostructures. Nat Commun 8(1):248
Soumyanarayanan A, Reyren N, Fert A, Panagopoulos C (2016) Emergent phenomena induced by spin-orbit coupling at surfaces and interfaces. Nature 539(7630):509–517
Benítez LA, Sierra JF, Savero Torres W, Arrighi A, Bonell F, Costache MV, Valenzuela SO (2017) Strongly anisotropic spin relaxation in graphene–transition metal dichalcogenide heterostructures at room temperature. Nat Phys 14(3):303–308
Gmitra M, Fabian J (2017) Proximity effects in bilayer graphene on monolayer WSe2: field-effect spin valley locking, spin-orbit valve, and spin transistor. Phys Rev Lett 119(14):146401
Mendes JB, Alves Santos O, Meireles LM, Lacerda RG, Vilela-Leao LH, Machado FL, Rodriguez-Suarez RL, Azevedo A, Rezende SM (2015) Spin-current to charge-current conversion and magnetoresistance in a hybrid structure of graphene and Yttrium Iron Garnet. Phys Rev Lett 115(22):226601
Zhang W, Sklenar J, Hsu B, Jiang W, Jungfleisch MB, Xiao J, Fradin FY, Liu Y, Pearson JE, Ketterson JB, Yang Z, Hoffmann A (2016) Research update: spin transfer torques in permalloy on monolayer MoS2. APL Mater 4(3):032302
Liang S, Yang H, Renucci P, Tao B, Laczkowski P, Mc-Murtry S, Wang G, Marie X, George JM, Petit-Watelot S, Djeffal A, Mangin S, Jaffres H, Lu Y (2017) Electrical spin injection and detection in molybdenum disulfide multilayer channel. Nat Commun 8:14947
Shao Q, Yu G, Lan YW, Shi Y, Li MY, Zheng C, Zhu X, Li LJ, Amiri PK, Wang KL (2016) Strong Rashba–Edelstein effect-induced spin-orbit torques in monolayer transition metal dichalcogenide/ferromagnet bilayers. Nano Lett 16(12):7514–7520
MacNeill D, Stiehl GM, Guimaraes MHD, Buhrman RA, Park J, Ralph DC (2016) Control of spin–orbit torques through crystal symmetry in WTe2/ferromagnet bilayers. Nat Phys 13(3):300–305
Leutenantsmeyer JC, Ingla-Aynes J, Fabian J, van Wees BJ (2018) Observation of spin-valley-coupling-induced large spin-lifetime anisotropy in bilayer graphene. Phys Rev Lett 121(12):127702
Tombros N, Jozsa C, Popinciuc M, Jonkman HT, van Wees BJ (2007) Electronic spin transport and spin precession in single graphene layers at room temperature. Nature 448(7153):571–574
Cho S, Chen Y-F, Fuhrer MS (2007) Gate-tunable graphene spin valve. Appl Phys Lett 91(12):123105
Michetti P, Recher P, Iannaccone G (2010) Electric field control of spin rotation in bilayer graphene. Nano Lett 10(11):4463–4469
Lin X, Su L, Si Z, Zhang Y, Bournel A, Zhang Y, Klein J-O, Fert A, Zhao W (2017) Gate-driven pure spin current in graphene. Phys Rev Appl 8(3):034006
Ghiasi TS, Ingla-Aynes J, Kaverzin AA, van Wees BJ (2017) Large proximity-induced spin lifetime anisotropy in transition-metal dichalcogenide/graphene heterostructures. Nano Lett 17(12):7528–7532
Dlubak B, Martin M-B, Deranlot C, Servet B, Xavier S, Mattana R, Sprinkle M, Berger C, De Heer WA, Petroff F, Anane A, Seneor P, Fert A (2012) Highly efficient spin transport in epitaxial graphene on SiC. Nat Phys 8(7):557–561
Ingla-Aynes J, Meijerink RJ, Wees BJ (2016) Eighty-eight percent directional guiding of spin currents with 90 um relaxation length in bilayer graphene using carrier drift. Nano Lett 16(8):4825–4830
Churchill HOH, Jarillo-Herrero P (2014) Phosphorus joins the family. Nat Nanotechnol 9(5):330–331
Wang X, Jones AM, Seyler KL, Tran V, Jia Y, Zhao H, Wang H, Yang L, Xu X, Xia F (2015) Highly anisotropic and robust excitons in monolayer black phosphorus. Nat Nanotechnol 10(6):517–521
Li L, Yu Y, Ye GJ, Ge Q, Ou X, Wu H, Feng D, Chen XH, Zhang Y (2014) Black phosphorus field-effect transistors. Nat Nanotechnol 9(5):372–377
Avsar A, Tan JY, Kurpas M, Gmitra M, Watanabe K, Taniguchi T, Fabian J, Özyilmaz B (2017) Gate-tunable black phosphorus spin valve with nanosecond spin lifetimes. Nat Phys 13(9):888–893
Cai K, Yang M, Ju H, Wang S, Ji Y, Li B, Edmonds KW, Sheng Y, Zhang B, Zhang N, Liu S, Zheng H, Wang K (2017) Electric field control of deterministic current-induced magnetization switching in a hybrid ferromagnetic/ferroelectric structure. Nat Mater 16(7):712–716
Dey P, Yang L, Robert C, Wang G, Urbaszek B, Marie X, Crooker SA (2017) Gate-controlled spin-valley locking of resident carriers in WSe2 monolayers. Phys Rev Lett 119:137401
Garcia JH, Vila M, Cummings AW, Roche S (2018) Spin transport in graphene/transition metal dichalcogenide heterostructures. Chem Soc Rev 47(9):3359–3379
Cardoso C, Soriano D, Garcia-Martinez NA, Fernandez-Rossier J (2018) Van der Waals spin valves. Phys Rev Lett 121(6):067701
Yan W, Txoperena O, Llopis R, Dery H, Hueso LE, Casanova F (2016) A two-dimensional spin field-effect switch. Nat Commun 7:13372
Dankert A, Dash SP (2017) Electrical gate control of spin current in van der Waals heterostructures at room temperature. Nat Commun 8:16093
Mellnik AR, Lee JS, Richardella A, Grab JL, Mintun PJ, Fischer MH, Vaezi A, Manchon A, Kim EA, Samarth N, Ralph DC (2014) Spin-transfer torque generated by a topological insulator. Nature 511(7510):449–451
Avci CO, Quindeau A, Pai CF, Mann M, Caretta L, Tang AS, Onbasli MC, Ross CA, Beach GS (2017) Current-induced switching in a magnetic insulator. Nat Mater 16(3):309–314
Khang NHD, Ueda Y, Hai PN (2018) A conductive topological insulator with large spin Hall effect for ultralow power spin-orbit torque switching. Nat Mater 17(9):808–813
Wang Y, Zhu D, Wu Y, Yang Y, Yu J, Ramaswamy R, Mishra R, Shi S, Elyasi M, Teo KL, Wu Y, Yang H (2017) Room temperature magnetization switching in topological insulator-ferromagnet heterostructures by spin-orbit torques. Nat Commun 8(1):1364
Fan Y, Upadhyaya P, Kou X, Lang M, Takei S, Wang Z, Tang J, He L, Chang LT, Montazeri M, Yu G, Jiang W, Nie T, Schwartz RN, Tserkovnyak Y, Wang KL (2014) Magnetization switching through giant spin-orbit torque in a magnetically doped topological insulator heterostructure. Nat Mater 13(7):699–704
Fan Y, Kou X, Upadhyaya P, Shao Q, Pan L, Lang M, Che X, Tang J, Montazeri M, Murata K, Chang L-T, Akyol M, Yu G, Nie T, Wong KL, Liu J, Wang Y, Tserkovnyak Y, Wang KL (2016) Electric-field control of spin–orbit torque in a magnetically doped topological insulator. Nat Nanotechnol 11(4):352–359
Jiang S, Li L, Wang Z, Mak KF, Shan J (2018) Controlling magnetism in 2D CrI3 by electrostatic doping. Nat Nanotechnol 13(7):549–553
Wang Z, Zhang T, Ding M, Dong B, Li Y, Chen M, Li X, Huang J, Wang H, Zhao X, Li Y, Li D, Jia C, Sun L, Guo H, Ye Y, Sun D, Chen Y, Yang T, Zhang J, Ono S, Han Z, Zhang Z (2018) Electric-field control of magnetism in a few-layered van der Waals ferromagnetic semiconductor. Nat Nanotechnol 13(7):554–559
Deng Y, Yu Y, Song Y, Zhang J, Wang NZ, Wu YZ, Zhu J, Wang J, Chen XH, Zhang Y (2018) Gate-tunable room-temperature ferromagnetism in two dimensional Fe3GeTe2. Nature 563:94
Djayaprawira DD, Tsunekawa K, Nagai M, Maehara H, Yamagata S, Watanabe N, Yuasa S, Suzuki Y, Ando K (2005) 230% room-temperature magnetoresistance in CoFeB∕MgO∕CoFeB magnetic tunnel junctions. Appl Phys Lett 86(9):092502
Karpan VM, Giovannetti G, Khomyakov PA, Talanana M, Starikov AA, Zwierzycki M, van den Brink J, Brocks G, Kelly PJ (2007) Graphite and graphene as perfect spin filters. Phys Rev Lett 99(17):176602
Zhang H, Ye M, Wang Y, Quhe R, Pan Y, Guo Y, Song Z, Yang J, Guo W, Lu J (2016) Magnetoresistance in Co/2D MoS2/Co and Ni/2D MoS2/Ni junctions. Phys Chem Chem Phys 18(24):16367–16376
Iqbal MZ, Siddique S, Hussain G, Iqbal MW (2016) Room temperature spin valve effect in the NiFe/Gr–hBN/Co magnetic tunnel junction. J Mater Chem C 4(37):8711–8715
Song T (2018) Giant tunneling magnetoresistance in spin-filter van der Waals heterostructures. Science 360:1214–1218
Pan L, Huang L, Zhong M, Jiang XW, Deng HX, Li J, Xia JB, Wei Z (2018) Large tunneling magnetoresistance in magnetic tunneling junctions based on two-dimensional CrX3 (X = Br, I) monolayers. Nanoscale 10(47):22196–22202
Wang Z, Gutierrez-Lezama I, Ubrig N, Kroner M, Gibertini M, Taniguchi T, Watanabe K, Imamoglu A, Giannini E, Morpurgo AF (2018) Very large tunneling magnetoresistance in layered magnetic semiconductor CrI3. Nat Commun 9(1):2516
Kim HH, Yang B, Patel T, Sfigakis F, Li C, Tian S, Lei H, Tsen AW (2018) One million percent tunnel magnetoresistance in a magnetic van der Waals heterostructure. Nano Lett 18(8):4885–4890
Song T, Tu MW, Carnahan C, Cai X, Taniguchi T, Watanabe K, McGuire MA, Cobden DH, Xiao D, Yao W, Xu X (2019) Voltage control of a van der Waals spin-filter magnetic tunnel junction. Nano Lett 19(2):915–920
Wang Z, Sapkota D, Taniguchi T, Watanabe K, Mandrus D, Morpurgo AF (2018) Tunneling spin valves based on Fe3GeTe2/hBN/Fe3GeTe2 van der Waals heterostructures. Nano Lett 18(7):4303–4308
Zhou J, Qiao J, Duan CG, Bournel A, Wang KL, Zhao W (2019) Large tunneling magnetoresistance in VSe2/MoS2 magnetic tunnel junction. ACS Appl Mater Interfaces 11(19):17647–17653
Datta S, Das B (1990) Electronic analog of the electro-optic modulator. Appl Phys Lett 56(7):665–667
Britnell L, Gorbachev RV, Jalil R, Belle BD, Schedin F, Mishchenko A, Georgiou T, Katsnelson MI, Eaves L, Morozov SV, Peres NMR, Geim K, Novoselov KS, Ponomarenko LA (2012) Field-effect tunneling transistor based on vertical graphene heterostructures. Science 335:947–950
Avsar A, Vera-Marun IJ, Tan JY, Koon GKW, Watanabe K, Taniguchi T, Adam S, Özyilmaz B (2016) Electronic spin transport in dual-gated bilayer graphene. NPG Asia Mater 8(6):e274–e274
Jiang S, Li L, Wang Z, Shan J, Mak KF (2019) Spin tunnel field-effect transistors based on two-dimensional van der Waals heterostructures. Nat Electron 2(4):159–163
Dery H, Cywiński Ł, Sham LJ (2006) Spin transference and magnetoresistance amplification in a transistor. Phys Rev B 73(16):161307
Behin-Aein B, Datta D, Salahuddin S, Datta S (2010) Proposal for an all-spin logic device with built-in memory. Nat Nanotechnol 5(4):266–270
Wen H, Dery H, Amamou W, Zhu T, Lin Z, Shi J, Žutić I, Krivorotov I, Sham LJ, Kawakami RK (2016) Experimental demonstration of xor operation in graphene magnetologic gates at room temperature. Phys Rev Appl 5(4):044003
Dery H, Dalal P, Cywinski L, Sham LJ (2007) Spin-based logic in semiconductors for reconfigurable large-scale circuits. Nature 447(7144):573–576
Kim WY, Kim HD, Kim TT, Park HS, Lee K, Choi HJ, Lee SH, Son J, Park N, Min B (2016) Graphene-ferroelectric metadevices for nonvolatile memory and reconfigurable logic-gate operations. Nat Commun 7:10429
Dery H, Wu H, Ciftcioglu B, Huang M, Song Y, Kawakami R, Shi J, Krivorotov I, Zutic I, Sham LJ (2012) Nanospintronics based on magnetologic gates. IEEE Trans Electron Devices 59(1):259–262
Zeng M, Su H, Zhang C, Feng Y (2011) Graphene-based spin logic gates. Appl Phys Lett 98(9):092110
Su G, Wu X, Tong W, Duan C (2016) Two-dimensional layered materials-based spintronics. Spin 05(04):1540011
Feng YP, Shen L, Yang M, Wang A, Zeng M, Wu Q, Chintalapati S, Chang C-R (2017) Prospects of spintronics based on 2D materials. WIREs Comput Mol Sci 7(5):e1313
Maassen J, Ji W, Guo H (2011) Graphene spintronics: the role of ferromagnetic electrodes. Nano Lett 11(1):151–155
Wang H, Liu Y, Wu P, Hou W, Jiang Y, Li X, Pandey C, Chen D, Yang Q, Wang H, Wei D, Lei N, Kang W, Wen L, Nie T, Zhao W, Wang KL (2020) Above room-temperature ferromagnetism in wafer-scale two-dimensional van der Waals Fe3GeTe2 tailored by a topological insulator. ACS Nano 14(8):10045–10053
Fei Z, Zhao W, Palomaki TA, Sun B, Miller MK, Zhao Z, Yan J, Xu X, Cobden DH (2018) Ferroelectric switching of a two-dimensional metal. Nature 560(7718):336–339
Alghamdi M, Lohmann M, Li J, Jothi PR, Shao Q, Aldosary M, Su T, Fokwa BPT, Shi J (2019) Highly efficient spin-orbit torque and switching of layered ferromagnet Fe3GeTe2. Nano Lett 19(7):4400–4405
This work was supported by the joint fund of the National Natural Science Foundation Committee of China Academy of Engineering Physics (NSAF) (U1630108). This research was partially carried out at the USTC Center for Micro and Nanoscale Research and Fabrication.
The joint fund of the National Natural Science Foundation Committee of China Academy of Engineering Physics (NSAF) (U1630108).
The authors declare that they have no conflict of interest.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Hu, G., Xiang, B. Recent Advances in Two-Dimensional Spintronics. Nanoscale Res Lett 15, 226 (2020). https://doi.org/10.1186/s11671-020-03458-y
- 2D spintronics
- Topological insulator
- Van der Waals magnet
- Spin-charge conversion
- Spin transport
- Spin manipulation