Half-Metallicity in MnPSe3 Exfoliated Nanosheet with Carrier Doping

Ferroelectrically controlled electromagnetic and transport properties of VN2H2/Al2O3 van der Waals multiferroic heterostructures

The vertical integration of a ferromagnetic monolayer and a ferroelectric monolayer into van der Waals heterostructures offers a promising route to achieve two-dimensional multiferroic semiconductors owing to the lack of intrinsic single-phase multiferroic materials in nature. In this study, we propose a VN2H2/Al2O3 van der Waals magnetoelectric multiferroic heterostructure and investigate its electronic, magnetic, and transport properties using density functional theory combined with the Boltzmann transport theory. The VN2H2 monolayer is a room-temperature ferromagnetic semiconductor with a band gap of 0.24 eV and a Curie temperature of 411 K, while the Al2O3 monolayer is a ferroelectric semiconductor with a polarization value of 0.11 C m-2. In the VN2H2/Al2O3 van der Waals heterostructures, the conversion between the metal and the semiconductor can be controlled by altering the polarization of the Al2O3 layer. The VN2H2/Al2O3 van der Waals heterostructure retains room-temperature ferromagnetism, and the reverse of polarization is accompanied with a change in the direction of the easy magnetization axis. In addition, electrostatic doping can significantly improve the conductivity of the downward polarization state and transform the upward polarization state from a metal to a half-metal, achieving 100% spin polarization. Our results thus pave the way for achieving highly tunable electromagnetic and transport properties in van der Waals magnetoelectric heterostructures, which have potential applications in next-generation low-power logic and memory devices.

Bulk photovoltaic effect and high mobility in the polar 2D semiconductor SnP2Se6

The growth of layered 2D compounds is a key ingredient in finding new phenomena in quantum materials, optoelectronics, and energy conversion. Here, we report SnP2Se6, a van der Waals chiral (R3 space group) semiconductor with an indirect bandgap of 1.36 to 1.41 electron volts. Exfoliated SnP2Se6 flakes are integrated into high-performance field-effect transistors with electron mobilities >100 cm2/Vs and on/off ratios >106 at room temperature. Upon excitation at a wavelength of 515.6 nanometer, SnP2Se6 phototransistors show high gain (>4 × 104) at low intensity (≈10-6 W/cm2) and fast photoresponse (< 5 microsecond) with concurrent gain of ≈52.9 at high intensity (≈56.6 mW/cm2) at a gate voltage of 60 V across 300-nm-thick SiO2 dielectric layer. The combination of high carrier mobility and the non-centrosymmetric crystal structure results in a strong intrinsic bulk photovoltaic effect; under local excitation at normal incidence at 532 nm, short circuit currents exceed 8 mA/cm2 at 20.6 W/cm2.

A Route to Two-Dimensional Room-Temperature Organometallic Multiferroics: The Marriage of d-p Spin Coupling and Structural Inversion Symmetry Breaking

Two-dimensional (2D) room-temperature multiferroic materials are highly desirable but still very limited. Herein, we propose a potential strategy to obtain such materials in 2D metal-organic frameworks (MOFs) by utilizing the d-p direct spin coupling in conjunction with center-symmetry-breaking six-membered heterocyclic rings. Based on this strategy, a screening of 128 2D MOFs results in the identification of three multiferroics, that is, Cr(1,2-oxazine)2, Cr(1,2,4-triazine)2, and Cr(1,2,3,4-trazine)2, simultaneously exhibiting room-temperature ferrimagnetism and ferroelectricity/antiferroelectricity. The room-temperature ferrimagnetic order (306-495 K) in these MOFs originates from the strong d-p direct magnetic exchange interaction between Cr cations and ligand anions. Specifically, Cr(1,2-oxazine)2 exhibits ferroelectric behavior with an out-of-plane polarization of 4.24 pC/m, whereas the other two manifest antiferroelectric characteristics. Notably, all three materials present suitable polarization switching barriers (0.18-0.31 eV). Furthermore, these MOFs are all bipolar magnetic semiconductors with moderate band gaps, in which the spin direction of carriers can be manipulated by electrical gating.

Carrier doping modulates the magnetoelectronic and magnetic anisotropic properties of two-dimensional MSi2N4 (M = Cr, Mn, Fe, and Co) monolayers

Through extensive density functional theory (DFT) calculations, our investigation delves into the stability, electrical characteristics, and magnetic behavior of monolayers (MLs) of MSi2N4. Computational analyses indicate intrinsic antiferromagnetic (AFM) orders within the MSi2N4 MLs, as a result of direct exchange interactions among transition metal (M) atoms. We further find that CrSi2N4 and CoSi2N4 MLs with primitive cells (pcells) exhibit half-metallic properties, with respective spin-β electron gaps of 3.661 and 2.021 eV. In contrast, MnSi2N4 and FeSi2N4 MLs with pcells act as semiconductors, having energy gaps of 0.427 and 0.282 eV, respectively. When the SOC is considered, the CrSi2N4, MnSi2N4 and FeSi2N4 MLs are metals, while the CoSi2N4 ML is a semiconductor. Our findings imply the dynamics and thermodynamic stability of MSi2N4 MLs. We have also explored the influence of carrier doping on the electromagnetic attributes of MSi2N4 MLs. Interestingly, charge doping could transform CrSi2N4, MnSi2N4, and CoSi2N4 MLs from their original AFM state into a ferromagnetic (FM) order. Moreover, carrier doping transformed CrSi2N4 and CoSi2N4 MLs from spin-polarized metals to half-metals (HMs). It is of particular note that doping of CrSi2N4 MLs with +0.9 e per pcell or more holes caused a switch in the easy axis (EA) to the [001] axis. The demonstrated intrinsic AFM order, excellent thermodynamic and kinetic stability, adjustable magnetism, and half-metallicity of the MSi2N4 family suggest its promising potential for applications in the realm of spintronics.

A novel 2D intrinsic metal-free ferromagnetic semiconductor Si3C8 monolayer

Metal-free magnets, a special kind of ferromagnetic (FM) material, have evolved into an important branch of magnetic materials for spintronic applications. We herein propose a silicon carbide (Si3C8) monolayer and investigate its geometric, electronic, and magnetic properties by using first-principles calculations. The thermal and dynamical stability of the Si3C8 monolayer was confirmed by ab initio molecular dynamics and phonon dispersion simulations. Our results show that the Si3C8 monolayer is a FM semiconductor with a band gap of 1.76 eV in the spin-down channel and a Curie temperature of 22 K. We demonstrate that the intrinsic magnetism of the Si3C8 monolayer is derived from pz orbitals of C atoms via superexchange interactions. Furthermore, the half-metallic state in the FM Si3C8 monolayer can be induced by electron doping. Our work not only illustrates that carrier doping could manipulate the magnetic states of the FM Si3C8 monolayer but also provides an idea to design two-dimensional metal-free magnetic materials for spintronic applications.

A Universal Strategy for Synthesis of 2D Ternary Transition Metal Phosphorous Chalcogenides

The 2D ternary transition metal phosphorous chalcogenides (TMPCs) have attracted extensive research interest due to their widely tunable band gap, rich electronic properties, inherent magnetic and ferroelectric properties. However, the synthesis of TMPCs via chemical vapor deposition (CVD) is still challenging since it is difficult to control reactions among multi-precursors. Here, a subtractive element growth mechanism is proposed to controllably synthesize the TMPCs. Based on the growth mechanism, the TMPCs including FePS3 , FePSe3 , MnPS3 , MnPSe3 , CdPS3 , CdPSe3 , In2 P3 S9 , and SnPS3 are achieved successfully and further confirmed by Raman, second-harmonic generation (SHG), and scanning transmission electron microscopy (STEM). The typical TMPCs-SnPS3 shows a strong SHG signal at 1064 nm, with an effective nonlinear susceptibility χ(2) of 8.41 × 10-11  m V-1 , which is about 8 times of that in MoS2 . And the photodetector based on CdPSe3 exhibits superior detection performances with responsivity of 582 mA W-1 , high detectivity of 3.19 × 1011  Jones, and fast rise time of 611 µs, which is better than most previously reported TMPCs-based photodetectors. These results demonstrate the high quality of TMPCs and promote the exploration of the optical properties of 2D TMPCs for their applications in optoelectronics.

Bipolar Rashba Semiconductors: A Class of Nonmagnetic Materials for Electrical Spin Manipulation

The realization of the electrical control of spin is highly desirable. One promising approach is by regulating the Rashba spin-orbit coupling effect of materials through external electric fields. However, this method requires materials to possess either a high electric field response and a large Rashba constant or the simultaneous presence of Rashba splitting and ferroelectric polarization. These stringent requirements result in a scarcity of suitable materials. In order to surpass these limitations and exploit a new prospect for spin manipulation via the Rashba effect, a conceptual class of materials named bipolar Rashba semiconductors (BRS) is proposed, whose valence band and conduction band possess opposite spin texture directions when approaching the Fermi level. The unique electronic structure of BRS makes it feasible to reverse the spin precession by simply applying a gate voltage. The existence of BRS is confirmed through first-principles calculations on the two-dimensional (2D) material AlBiS3.

Recent progress in 2D bipolar magnetic semiconductors

Bipolar magnetic semiconductor (BMS) is a class of magnetic semiconductors, whose valence band maximum and conduction band minimum are fully spin-polarized with opposite spin directions. Due to the special energy band, half-metallicity can be easily obtained in BMS by gate voltage, and the spin polarization can be reversed between spin-up and down when the gate voltage switches from positive to negative. BMSs have great potential applications in spintronic devices, such as the field-effect spin valves, spin filters and spin transistors,etc. With the rapid progress of the two-dimensional (2D) magnetic materials, researchers have identified a series of potential intrinsic 2D BMS materials using high-throughput computational methods. Additionally, methods such as doping, application of external stress, introduction of external fields, stacking of interlayer antiferromagnetic semiconductors, and construction of Janus structures have endowed existing materials with BMS properties. This paper reviews the research progress of 2D BMS. These advancements provide crucial guidance for the design and synthesis of BMS materials and offer innovative pathways for the future development of spintronics.

Metal Phosphorous Chalcogenide: A Promising Material for Advanced Energy Storage Systems

The development of efficient and affordable electrode materials is crucial for clean energy storage systems, which are considered a promising strategy for addressing energy crises and environmental issues. Metal phosphorous chalcogenides (MPX3 ) are a fascinating class of two-dimensional materials with a tunable layered structure and high ion conductivity, making them particularly attractive for energy storage applications. This review article aims to comprehensively summarize the latest research progress on MPX3 materials, with a focus on their preparation methods and modulation strategies. Additionally, the diverse applications of these novel materials in alkali metal ion batteries, metal-air batteries, and all-solid-state batteries are highlighted. Finally, the challenges and opportunities of MPX3 materials are presented to inspire their better potential in energy storage applications. This review provides valuable insights into the promising future of MPX3 materials in clean energy storage systems.

Chemically Controlled Reversible Magnetic Phase Transition in Two-Dimensional Organometallic Lattices

Developing an efficient method to reversibly control materials' spin order is urgently needed but challenging in spintronics. Though various physical field control methods have been advancing, the chemical control of spin is little exploited. Here, we propose a chemical means for such spin manipulation, i.e., utilizing the well-known lactim-lactam tautomerization to reversibly modulate the magnetic phase transition in two-dimensional (2D) organometallic lattices. The proposal is verified by theoretically designing several 2D organometallic frameworks with antiferromagnetic to ferrimagnetic spin order transformation modulated by lactim-lactam tautomerization on organic linkers. The transition originates from the change in spin states of organic linkers (from singlet to doublet) via tautomerization. Such a transition further switches materials' electronic structures from normal semiconductors with zero spin polarization to bipolar magnetic semiconductors with valence and conduction band edges 100% spin polarized in opposite spin channels. Moreover, the magnitude of magnetic anisotropy energy also enhances by 5- to 9-fold.

Probing Active Sites on Pristine and Defective MnPX3 (X: S and Se) Monolayers for Electrocatalytic Water Splitting

The state-of-the-art density functional theory approach was used to study the structural and electronic properties of pristine and defective MnPX3 monolayers as well as their activity toward water and hydrogen evolution reaction (HER) catalytic performance. The adsorption behavior of H2O on a pristine MnPX3 structure is of physisorption nature, whereas the adsorption energy is significantly increased for the defective structures. At the same time, the water dissociation process is more energetically favorable, and the reactivity of MnPX3 is determined by the vacancy configuration. Following Nørskov's approach, the HER catalytic performance is evaluated by calculating the hydrogen adsorption free energy on the respective MnPX3 surface. Our calculation results demonstrate that defective 2D MnPX3 with low coordinated P shows significantly higher HER performance compared to the pristine counterpart.

Bilayer hexagonal structure MnN2 nanosheets with room-temperature ferromagnetic half-metal behavior and a tunable electronic structure

Two-dimensional (2D) layered materials have atomically thin thickness and outstanding physical properties, attracting intensive research in the past year. As one of these materials, a 2D magnet is an ideal platform for fundamental physics research and magnetic device development. Recently, a non-MoS2-type geometry was found to be more favorable in 2D transition-metal dinitrides. In this work, driven by this new configuration, we perform a comprehensive first-principles study on the bilayer hexagonal structure of 2D manganese dinitrides. Our results show that 2D MnN2 is a ferromagnetic half-metal at its ground state with 100% spin-polarization ratio at the Fermi energy level. The phonon spectrum calculation and ab initio molecular dynamics simulation show that the 2D MnN2 crystal has a high thermodynamic stability and its 2D lattice can be retained at room-temperature. Monte Carlo simulations based on the Heisenberg model predict a Curie temperature of over 563 K and its electronic properties can be regulated by biaxial strain. The half-metallic states are mainly contributed by Mn d orbitals, and the magnetic exchange of the system mainly comes from the Mn-N-Mn super-exchange. The p-d orbital hybridization will provide a small antiparallel magnetic moment of N atoms, and the p-orbital dangling bond can be eliminated by oxidation to enhance the total magnetic moment of the system. The study of magnetic anisotropy energy indicates that the easy magnetization axis is in-plane and hybridization between Mn dyz and dz2 orbitals gives the largest magnetic anisotropy contribution. In view of these results, we consider that novel 2D MnN2 is one of the most promising two-dimensional materials for nano-spintronic applications.

Magnetism-Induced Band-Edge Shift as the Mechanism for Magnetoconductance in CrPS4 Transistors

Transistors realized on the 2D antiferromagnetic semiconductor CrPS4 exhibit large magnetoconductance due to magnetic-field-induced changes in the magnetic state. The microscopic mechanism coupling the conductance and magnetic state is not understood. We identify it by analyzing the evolution of the parameters determining the transistor behavior─carrier mobility and threshold voltage─with temperature and magnetic field. For temperatures T near the Néel temperature TN, the magnetoconductance originates from a mobility increase due to the applied magnetic field that reduces spin fluctuation induced disorder. For T ≪ TN, instead, what changes is the threshold voltage, so that increasing the field at fixed gate voltage increases the density of accumulated electrons. The phenomenon is explained by a conduction band-edge shift correctly predicted by the ab initio calculations. Our results demonstrate that the band structure of CrPS4 depends on its magnetic state and reveal a mechanism for magnetoconductance that had not been identified earlier.

First-Principles Study on Mechanical, Electronic, and Magnetic Properties of Room Temperature Ferromagnetic Half-Metal MnNCl Monolayer

Two-dimensional ferromagnetic (FM) half-metals are highly desirable for the development of multifunctional spintronic nano-devices due to their 100% spin polarization and possible interesting single-spin electronic states. Herein, using first-principles calculations based on density functional theory (DFT) with the Perdew-Burke-Ernzerhof (PBE) functional, we demonstrate that the MnNCl monolayer is a promising FM half-metal for spintronics. Specifically, we systematically investigated its mechanical, magnetic, and electronic properties. The results reveal that the MnNCl monolayer has superb mechanic, dynamic, and thermal (ab initio molecular dynamics (AIMD) simulation at 900 K) stability. More importantly, its intrinsic FM ground state has a large magnetic moment (6.16 μ_B), a large magnet anisotropy energy (184.5 μeV), an ultra-high Curie temperature (952 K), and a wide direct band gap (3.10 eV) in the spin-down channel. Furthermore, by applying biaxial strain, the MnNCl monolayer can still maintain its half-metallic properties and shows an enhancement of magnetic properties. These findings establish a promising new two-dimensional (2D) magnetic half-metal material, which should expand the library of 2D magnetic materials.

Transmutation Engineering Makes a Large Class of Stable and Exfoliable A3BX2 Compounds with Exceptional High Magnetic Critical Temperatures and Exotic Electronic Properties

We establish a robust protocol for materials innovation based on our proposed transmutation engineering strategy combined with combinatorial chemistry and hierarchical high-throughput screening to make a large class of layered 2D A₃BX₂ materials. After several rounds of efficient screening, 60 types of easily exfoliable and highly stable A₃BX₂ monolayers have been obtained. Excitingly, four representative monolayers (ferromagnetic Fe₃SiS₂ and Fe₃GeS₂, antiferromagnetic Mn₃PbTe₂ and Co₃GeSe₂) demonstrate quite high magnetic critical temperatures of 600 (T_C), 630 (T_C), 770 (T_N), and 510 K (T_N), respectively. Through electronic fingerprint identification, the magnetic exchange mechanism is fundamentally unveiled at the atomic level in combination with a local chemical topology environment and crystal/exchange field. Furthermore, two simple and effective unified descriptors are proposed to perfectly explain the origin of magnetic strain regulation. Some intriguing materials (featuring double Dirac cones, node-loops, and ultrahigh Fermi velocities) are expected to be used in high-speed and low-dissipation nanodevices. This material family forms a dataset, which establishes a platform to discover and explore unexpected physicochemcial properties and develop promising applications under different circumstances. The chemical trends of diverse properties for this class of materials are revealed, which offers guiding insights for the development of spintronics and nanoelectronics with the target of exploiting both spin and charge degrees of freedom directed functional materials design and screening.

Gate-Controlled Magnetotransport and Electrostatic Modulation of Magnetism in 2D Magnetic Semiconductor CrPS4

Using field-effect transistors (FETs) to explore atomically thin magnetic semiconductors with transport measurements is difficult, because the very narrow bands of most 2D magnetic semiconductors cause carrier localization, preventing transistor operation. Here, it is shown that exfoliated layers of CrPS₄ -a 2D layered antiferromagnetic semiconductor whose bandwidth approaches 1 eV-allow the realization of FETs that operate properly down to cryogenic temperature. Using these devices, conductance measurements as a function of temperature and magnetic field are performed to determine the full magnetic phase diagram, which includes a spin-flop and a spin-flip phase. The magnetoconductance, which depends strongly on gate voltage, is determined. reaching values as high as 5000% near the threshold for electron conduction. The gate voltage also allows the magnetic states to be tuned, despite the relatively large thickness of the CrPS₄ multilayers employed in the study. The results show the need to employ 2D magnetic semiconductors with sufficiently large bandwidth to realize properly functioning transistors, and identify a candidate material to realize a fully gate-tunable half-metallic conductor.

Spontaneous valley polarization and valley-nonequilibrium quantum anomalous Hall effect in Janus monolayer ScBrI

Topology and ferrovalley (FV) are two essential concepts in emerging device applications and the fundamental research field. To date, relevant reports are extremely rare about the coupling of FV and topology in a single system. By Monte Carlo (MC) simulations and first-principles calculations, a stable intrinsic FV ScBrI semiconductor with high Curie temperature (T_C) is predicted. Because of the combination of spin-orbital coupling (SOC) and exchange interaction, the Janus monolayer ScBrI shows a spontaneous valley polarization of 90 meV, which is located in the top valence band. For the magnetization direction perpendicular to the plane, the changes from FV to half-valley-metal (HVM), to valley-nonequilibrium quantum anomalous Hall effect (VQAHE), to HVM, and to FV can be induced by strain engineering. It is worth noting that there are no particular valley polarization and VQAHE states for in-plane (IP) magnetic anisotropy. By obtaining the real magnetic anisotropy energy (MAE) under different strains, due to spontaneous valley polarization, intrinsic out-of-plane (OOP) magnetic anisotropy, a chiral edge state, and a unit Chern number, the VQAHE can reliably appear between two HVM states. The increasing strains can induce VQAHE, which can be clarified by a band inversion between d_x²-y²/d_xy and d_z² orbitals, and a sign-reversible Berry curvature. Once synthesized, the Janus monolayer ScBrI would find more significant applications in topological electronic, valleytronic, and spintronic nanodevices.

Quintuple Function Integration in Two-Dimensional Cr(II) Five-Membered Heterocyclic Metal Organic Frameworks via Tuning Ligand Spin and Lattice Symmetry

Two-dimensional (2D) semiconductors (SCs) integrated with two or more functions are the cornerstone for constructing multifunctional nanodevices but remain largely limited. Here, by tuning the spin state of organic linkers and the symmetry/topology of crystal lattices, we predict a class of unprecedented multifunctional SCs in 2D Cr(II) five-membered heterocyclic metal organic frameworks that simultaneously possess auxetic effect, room-temperature ferrimagnetism, chiral ferroelectricity (FE), electrically reversible spin polarization, and topological nodal lines/points. Taking 2D Cr(TDZ)₂ (TDZ = 1.2.5-thiadiazole) as an exemplification, the auxetic effect is produced by the antitetra-chiral lattice structure. The high temperature ferrimagnetism originates from the strong d-p direct magnetic exchange interaction between Cr cations and TDZ doublet radical anions. Meanwhile, the clockwise-counterclockwise alignment of TDZ's dipoles results in unique 2D chiral FE with atomic-scale vortex-antivortex states. 2D Cr(TDZ)₂ is an intrinsic bipolar magnetic SC where half-metallic conduction with switchable spin-polarization direction can be induced by applying a gate voltage. In addition, the symmetry of the little group C₄ of the lattice structure endows 2D Cr(TDZ)₂ with topological nodal lines and a quadratic nodal point in the Brillouin zone near the Fermi level.

Enhanced Curie temperature and conductivity of van der Waals ferromagnet MgV2S4via electrostatic doping

A van der Waals intrinsic ferromagnet with double magnetic atom layers is of great interest for both revealing fundamental physics and exploring promising applications in low-dimensional spintronics. Here, the magnetic and electronic properties of the van der Waals ferromagnet MgV₂S₄ monolayer are studied under electrostatic doping using first-principles calculations. A MgV₂S₄ monolayer presents the desired physical properties such as that of being a half-semiconductor with a direct bandgap of 1.21 eV and a ferromagnetic ground state, and having a high Curie temperature of 462 K. Unlike the robust ferromagnetic ground state, magnetic anisotropy and Curie temperature are sensitive to electrostatic doping. Meanwhile, the transition from a semiconductor to a half-metal and the significant improvement in conductivity under electrostatic doping make the MgV₂S₄ monolayer a promising candidate for low-dimensional spintronic field-effect transistors.

Tunable Valley and Spin Splittings in VSi2N4 Bilayers

The control and manipulation of the valley and spin degrees of freedom have received great interest in fundamental studies and advanced information technologies. Compared with magnetic means, it is highly desirable to realize more energy-efficient electric control of valley and spin. Using the first-principles calculations, we demonstrate tunable valley and spin degeneracy splittings in VSi₂N₄ bilayers, with the aid of the layered structure and associated electric control. Depending on different interlayer magnetic couplings and stacking orders, the VSi₂N₄ bilayers exhibit a variety of combinations of valley and spin degeneracies. Under the action of a vertical electric field, the degeneracy splittings become highly tunable for both the sign and the magnitude. As a result, a series of anomalous Hall currents can be selectively realized with varied indices of valley and spin. These intriguing features offer a practical way for designing energy-efficient devices based on the couplings between multiple electronic degrees of freedom.

Unexpected spontaneous symmetry breaking and diverse ferroicity in two-dimensional mono-metal phosphorus chalcogenides

Mono-metal phosphorus trichalcogenides (MPX₃) have attracted intensive interest due to their intriguing magnetic properties and potential applications. Generally, single-layer two-dimensional (2D) MPX₃ are believed to be centrosymmetric. However, we discovered that unexpected spontaneous symmetry breaking may occur in some 2D MPX₃, i.e., vertical P-P dimers move out of the plane and become tilted, leading to the structural stability being enhanced, the inversion symmetry being simultaneously broken, and ferroelectricity or ferroelasticity emerging. By systematically investigating the family (176) of 2D MPX₃, we found that 34 members undergo such symmetry breaking during geometric optimization, in which ten are identified to be dynamically stable. We show that the mismatch between the triangular sublattice of P-P dimers and the hexagonal sublattice of M atoms and the variable accommodation of P lone-pair electrons in different valence states of M atoms play dominant roles in the inversion symmetry breaking and the emergence of ferroicity. We obtained a ferroic atlas of the whole 2D MPX₃ family, which also includes many stable antiferromagnetic and non-ferroic members that have never been reported. Our work not only presents ferroelectricity in the 2D MPX₃ family but also reveals how diverse ferroicity emerges with various spontaneous symmetry breakings, which will be helpful for further exploration of 2D ferroic materials.

Designing a ferrimagnetic-ferroelastic multiferroic semiconductor in FeMoClO4 nanosheets via element substitution

Exploring two-dimensional multiferroic semiconductors, combined with ferro-/ferrimagnetism and ferroelasticity as well as large spin polarization around the valence band maximum (VBM) and conduction band minimum (CBM), is highly desirable but remains a challenging task. Here, via first-principles calculations, we predict such a material based on the square phase FeMoClO₄ nanosheet, which is experimentally accessible by exfoliating its layered bulk. Pristine FeMoClO₄ nanosheets are a weak antiferromagnet with zero spin polarization. After substituting nonmagnetic Mo with magnetic Mn, the resulting FeMnClO₄ nanosheet becomes ferrimagnetic with magnetic ordering temperature significantly enhanced from 14 to 127 K. Besides, the FeMnClO₄ nanosheet is a half semiconductor with its VBM and CBM 100% spin-polarized in the same spin direction. Interestingly, the initial square lattice is distorted into a rectangular one, inducing an in-plane ferroelasticity in the FeMnClO₄ nanosheet with a switching barrier of 27 meV per atom. Moreover, under ferroelastic transition, the orientation of the magnetic easy axis can be reversibly rotated by 90°, indicating a strong magnetoelastic coupling.

2D electrene LaH2monolayer: an ideal ferrovalley direct semiconductor with room-temperature ferromagnetic stability

In developing nonvolatile valleytronic devices, ferromagnetic (FM) ferrovalley semiconductors are critically needed due to the existence of spontaneous valley polarization. At present, however, the known real materials have various drawbacks towards practical applications, including the in-plane FM ground state, low Curie temperature (TC), small valley polarization, narrow energy window with clean polarized valley, and indirect bandgap. From first-principles calculations, here we predict anideal ferrovalley semiconductor, honeycomb LaH₂monolayer (ML), whose intrinsic properties can overcome all these shortcomings. We demonstrate that LaH₂ML, having satisfied structural stability, is a FM half-semiconducting electrene (La3+2H-⋅e-) with its magnetic moments localized at the lattice interstitial sites rather than La atoms. At the same time, LaH₂ML holds the following desired attributes: a robust out-of-plane FM ground state with a highTC(334 K), a sizable valley polarization (166 meV), a wide energy window (137 meV) harboring clean single-valley carriers, and a direct bandgap. These results identify a much needed ideal ferrovalley semiconductor candidate, holding the promising application potential in valleytronics and spintronics devices.

A novel exfoliated manganese phosphoselenide as a high-performance anode material for lithium ions storage

Layered manganese phosphoselenide (MnPSe3) is expected to be a potential anode for Li ions storage due to it combines the merits of phosphorus with metal selenide. It promotes charge transfer and ensures a high theoretical capacity of up to 746 mA h g−1. In this work, a comprehensive study clearly demonstrated that bulk MnPSe3 electrode is the inability to maintain the integrity of the structure with severe detectable fracture or pulverization after full lithiation/delithiation, resulting in poor rate capability and cycling stability. Additionally, exfoliated few-layered MnPSe3 nanoflakes by the ultrasonic method show enhanced electrical conductivity and resistance to volume expansion. It has a high initial discharge/charge capacity reaching to 524/796 mA h g−1 and outstanding cycling stability with charge capacities of 709 mA h g−1 after 100 cycles at 0.2 A g−1 within the potential window of 0.005–3 V vs. Li+/Li. While further improving the cycles, the retention rate was still held at ∼72% after 350 cycles. This work provides new insights into exploiting new novel layered materials, such as MnPSe3 as anodes for lithium-ion batteries.

Emergence of ferrimagnetism in Li-intercalated NiPS3

Intercalation has become a powerful approach to tune the intrinsic properties and introduce novel phenomena in layered materials. Intercalating van der Waals (vdW) magnetic materials is a promising route to engineer the low-dimensional magnetism. Recently, metal thiophosphates,MPX₃, has been widely studied because their magnetic orders are highly tunable and persist down to the two-dimensional limit. In this work, we used electrochemical technique to intercalate Li into NiPS₃single crystals and found the emergence of ferrimagnetism at low temperature in Li-intercalated NiPS₃. Such tuning of magnetic properties highlights the effectiveness of intercalation, providing a novel strategy to manipulate the magnetism in vdW magnets.

A review of bipolar magnetic semiconductors from theoretical aspects

Spintronics, which employs electrons' spin degree of freedom in data storage and transmission, acts as a promising candidate for next-generation information technology owing to its improved processing speed and reduced power consumption. To seek and design materials with highly spin polarized carriers and find an efficient way to control the spin polarization direction of carriers are critical and urgent to spintronics applications. In this aspect, the bipolar magnetic semiconductor (BMS) serves as an ideal solution since it can generate currents with 100% spin polarization, and the direction of spin polarization is easily tunable by an external gate voltage. Up to now, there have been lots of BMSs predicted by first-principles calculations, however, most of them are extrinsically induced by chemical or physical modifications, and a generalized scheme for designing BMS materials is still lacking. This paper is aimed to briefly review the existing BMS materials designed by theoretical simulations, analyze the main obstacles to experimental realization, and put forward suggestions for future development.

Engineering van der Waals Materials for Advanced Metaphotonics

The outstanding chemical and physical properties of 2D materials, together with their atomically thin nature, make them ideal candidates for metaphotonic device integration and construction, which requires deep subwavelength light-matter interaction to achieve optical functionalities beyond conventional optical phenomena observed in naturally available materials. In addition to their intrinsic properties, the possibility to further manipulate the properties of 2D materials via chemical or physical engineering dramatically enhances their capability, evoking new science on light-matter interaction, leading to leaped performance of existing functional devices and giving birth to new metaphotonic devices that were unattainable previously. Comprehensive understanding of the intrinsic properties of 2D materials, approaches and capabilities for chemical and physical engineering methods, the resulting property modifications and novel functionalities, and applications of metaphotonic devices are provided in this review. Through reviewing the detailed progress in each aspect and the state-of-the-art achievement, insightful analyses of the outstanding challenges and future directions are elucidated in this cross-disciplinary comprehensive review with the aim to provide an overall development picture in the field of 2D material metaphotonics and promote rapid progress in this fast emerging and prosperous field.

The Magnetic Genome of Two-Dimensional van der Waals Materials

Magnetism in two-dimensional (2D) van der Waals (vdW) materials has recently emerged as one of the most promising areas in condensed matter research, with many exciting emerging properties and significant potential for applications ranging from topological magnonics to low-power spintronics, quantum computing, and optical communications. In the brief time after their discovery, 2D magnets have blossomed into a rich area for investigation, where fundamental concepts in magnetism are challenged by the behavior of spins that can develop at the single layer limit. However, much effort is still needed in multiple fronts before 2D magnets can be routinely used for practical implementations. In this comprehensive review, prominent authors with expertise in complementary fields of 2D magnetism (i.e., synthesis, device engineering, magneto-optics, imaging, transport, mechanics, spin excitations, and theory and simulations) have joined together to provide a genome of current knowledge and a guideline for future developments in 2D magnetic materials research.

Magnesene: a theoretical prediction of a metallic, fast, high-capacity, and reversible anode material for sodium-ion batteries

Sodium-ion batteries (SIBs) have attracted great attention owing to their low cost and inherent safety. High-performance anode materials for SIBs should possess intrinsically metallic characteristic and be composed of non-toxic, earth abundant, and lightweight elements. We predict a two-dimensional Mg material (named magnesene) to be an excellent anode material, which can meet these design requirements. It is demonstrated to be stable in terms of the cohesive energy, phonon spectrum, ab initio molecular dynamics simulation, and elastic constants. The magnesene monolayer exhibits good SIB performances, including a high storage capacity of 551.3 mA h g^-1, low diffusion energy barrier (0.16-0.19 eV), low open-circuit voltage (0.71-0.82 V), and small volume change (4.7%). Moreover, graphene or h-BN on top of magnesene could serve as a protective cover to preserve the performances of pristine magnesene, such as metallicity, strong Na adsorption capability, and fast ionic mobility. These intriguing theoretical findings make magnesene a promising anode material for SIBs.

Limited Ferromagnetic Interactions in Monolayers of MPS3 (M = Mn and Ni)

We present a systematic study of the electronic and magnetic properties of two-dimensional ordered alloys, consisting of two representative hosts (MnPS3 and NiPS3) of transition metal phosphorus trichalcogenides doped with 3d elements. For both hosts, our DFT + U calculations are able to qualitatively reproduce the ratios and signs of all experimentally observed magnetic couplings. The relative strength of all antiferromagnetic exchange couplings, both in MnPS3 and in NiPS3, can successfully be explained using an effective direct exchange model: it reveals that the third-neighbor exchange dominates in NiPS3 due to the filling of the t2g subshell, whereas for MnPS3, the first-neighbor exchange prevails, owing to the presence of the t2g magnetism. On the other hand, the nearest neighbor ferromagnetic coupling in NiPS3 can only be explained using a more complex superexchange model and is (also) largely triggered by the absence of the t2g magnetism. For the doped systems, the DFT + U calculations revealed that magnetic impurities do not affect the magnetic ordering observed in the pure phases, and thus, in general in these systems, ferromagnetism may not be easily induced by such a kind of elemental doping. However, unlike for the hosts, the first and second (dopant-host) exchange couplings are of similar order of magnitude. This leads to frustration in the case of antiferromagnetic coupling and may be one of the reasons of the observed lower magnetic ordering temperature of the doped systems.

Half-integer anomalous currents in 2D materials from a QFT viewpoint

Charge carriers in Dirac/Weyl semi-metals exhibit a relativistic-like behavior. In this work we propose a novel type of intrinsic half-integer Quantum Hall effect in 2D materials, thereby also offering a topological protection mechanism for the current. Its existence is rooted in the 2D parity anomaly, without any need for a perpendicular magnetic field. We conjecture that it may occur in disturbed honeycomb lattices where both spin degeneracy and time reversal symmetry are broken. These configurations harbor two distinct gap-opening mechanisms that, when occurring simultaneously, drive slightly different gaps in each valley, causing a net anomalous conductivity when the chemical potential is tuned to be between the distinct gaps. Some examples of promising material setups that fulfill the prerequisites of our proposal are also listed to motivate looking for the effect at the numerical and experimental level.

An intrinsic room-temperature half-metallic ferromagnet in a metal-free PN2 monolayer

In spintronics, the embodiment of abundance availability, long spin relaxation time, complete spin-polarization and high Curie temperature (T_C) in intrinsic metal-free half-metallic ferromagnets (MFHMFs) are highly desirable and challenging. In this work, employing density functional theory, we first propose a dynamically, thermally, and mechanically stable two-dimensional (2D) intrinsic MFHMF, i.e. a MoS₂-like PN₂ monolayer, which possesses not only completely spin-polarized half-metallicity, but also an above-room-temperature T_C (385 K). The half-metallic gap is calculated to be 1.70 eV, which can effectively prevent the spin-flip transition caused by thermal agitation. The mechanism of magnetism in the PN₂ monolayer is mainly derived from the p electron direct exchange interaction that separates from usual d-state magnetic materials. Moreover, the robustness of the ferromagnetism and half-metallicity is observed against an external strain and carrier (electron or hole) doping. Surprisingly, electron doping can effectively increase the Curie temperature of the PN₂ monolayer. The proposed research work provides an insight that PN₂ can be a promising candidate for realistic room-temperature metal-free spintronic applications.

Enhanced Curie Temperature of Two-Dimensional Cr(II) Aromatic Heterocyclic Metal-Organic Framework Magnets via Strengthened Orbital Hybridization

Two-dimensional (2D) metal-organic frameworks (MOFs) with room-temperature magnetism are highly desirable but challenging due to the weak superexchange interaction between metal atoms. For this purpose, strengthening the hybridization between metal ion and organic linkage presents an experiment-feasible chemical solution to enhance the Curie temperature. Here, we report three 2D Cr(II) aromatic heterocyclic MOF magnets with enhanced Curie temperature by bridging Cr(II) ions with pyrazine, 1,4-diphosphinine, and 1,4-diarsenin linkers, i.e., Cr(pyz)₂, Cr(diphos)₂, and Cr(diarse)₂, and using first-principles calculations. Our results show that Cr(pyz)₂, Cr(diphos)₂, and Cr(diarse)₂ are ferrimagnetic semiconductors. In particular, the Curie temperature of Cr(pyz)₂ is estimated to be about 344 K and could be enhanced to 512 and 437 K in Cr(diphos)₂ and Cr(diarse)₂ by strengthening the hybridization between Cr ions and organic linkers via d-π* direct exchange interaction. This study presents a prototype to obtain room-temperature magnetism in 2D Cr(II)-based MOF magnets for nanoscale spintronics applications.

Magnetism and perfect spin filtering in pristine MgCl2 nanoribbons modulated by edge modification

The search for new materials, with ideal electronic and magnetic properties for potential applications in nanoelectronics, has been extremely successful so far, and has paved the way for us to reimagine all technological devices. In the present work, we study the design of MgCl₂ nanoribbons for applications in nanoelectronics and spintronics, by employing first-principles calculations based on density functional theory (DFT) and non-equilibrium Greens function techniques. Our results show that the properties of MgCl₂ nanoribbons depend strongly not only on their geometrical form (armchair or zigzag) but also on the atoms at their edges. The armchair MgCl₂ nanoribbon is a semiconductor and the zigzag nanoribbons vary from semiconducting, to metallic, to ferromagnetic, and to half-metallic, depending on the edge terminations. All these nanoribbons are very stable, with a relatively low cohesive energy per atom, and their attributes are not affected by the width of the nanoribbon. From transport calculations, we observed partial spin filtering in the ferromagnetic nanoribbon and perfect spin filtering in the two half-metallic nanoribbons. Moreover, we show how the current versus voltage curves can be fully understood by analysing the alignment of the energy levels of the electrodes. Our results corroborate the promising use of single-layer MgCl₂ for the development of spintronics devices.

Mott-Hubbard insulating state for the layered van der Waals [Formula: see text] (X: S, Se) as revealed by NEXAFS and resonant photoelectron spectroscopy

A broad family of the nowadays studied low-dimensional systems, including 2D materials, demonstrate many fascinating properties, which however depend on the atomic composition as well as on the system dimensionality. Therefore, the studies of the electronic correlation effects in the new 2D materials is of paramount importance for the understanding of their transport, optical and catalytic properties. Here, by means of electron spectroscopy methods in combination with density functional theory calculations we investigate the electronic structure of a new layered van der Waals [Formula: see text] (X: S, Se) materials. Using systematic resonant photoelectron spectroscopy studies we observed strong resonant behavior for the peaks associated with the [Formula: see text] final state at low binding energies for these materials. Such observations clearly assign [Formula: see text] to the class of Mott-Hubbard type insulators for which the top of the valence band is formed by the hybrid Fe-S/Se electronic states. These observations are important for the deep understanding of this new class of materials and draw perspectives for their further applications in different application areas, like (opto)spintronics and catalysis.

Transition Metal-Free Half-Metallicity in Two-Dimensional Gallium Nitride with a Quasi-Flat Band

Two-dimensional half-metallicity without a transition metal is an attractive attribute for spintronics applications. On the basis of first-principles calculation, we revealed that a two-dimensional gallium nitride (2D-GaN), which was recently synthesized between graphene and SiC or wurtzite GaN substrate, exhibits half-metallicity due to its half-filled quasi-flat band. We found that graphene plays a crucial role in stabilizing a local octahedral structure, whose unusually high density of states due to a flat band leads to a spontaneous phase transition to its half-metallic phase from normal metal. It was also found that its half-metallicity is strongly correlated to the in-plane lattice constants and thus subjected to substrate modification. To investigate the magnetic property, we simplified its magnetic structure with a two-dimensional Heisenberg model and performed Monte Carlo simulation. Our simulation estimated its Curie temperature (T_C) to be ∼165 K under a weak external magnetic field, suggesting that transition metal-free 2D-GaN exhibiting p orbital-based half-metallicity can be utilized in future spintronics.

High Curie Temperature and Intrinsic Ferromagnetic Half-Metallicity in Mn2X3 (X = S, Se, Te) Nanosheets

Two-dimensional (2D) intrinsic half-metallic materials with room-temperature ferromagnetism, sizable magnetic anisotropy energy (MAE), and wide half-metallic gap are excellent candidates for pure spin generation, injection, and transport in nanospintronic applications. However, until now, such 2D half metallicity has been rarely observed in experiment. In this work, by using first-principles calculations, we design a series of such materials, namely, Mn₂X₃ (X = S, Se, Te) nanosheets, which could be obtained by controlling the thickness of synthesized α-MnX(111) nanofilm to a quintuple X-Mn-X-Mn-X layer. All these nanosheets are dynamically and thermally stable. Electronic and magnetic studies reveal they are intrinsic half metals with high Curie temperatures between 718 and 820 K, sizable MAEs with -1.843 meV/Mn for Mn₂Te₃ nanosheet, and wide half-metallic gaps from 1.55 to 1.94 eV. Above all, the outstanding features of Mn₂X₃ nanosheets make them promising in fabricating nanospintronic devices working at room temperature.

Tuning magnetism at the two-dimensional limit: a theoretical perspective

The discovery of two-dimensional (2D) magnetic materials provides an ideal testbed for manipulating the magnetic properties at the atomically thin and 2D limit. This review gives recent progress in the emergent 2D magnets and heterostructures, focusing on the theory side. We summarize different theoretical models, ranging from the atomic to micrometer-scale, used to describe magnetic orders. Then, the current strategies for tuning magnetism in 2D materials are further discussed, such as electric field, magnetic field, strain, optics, chemical functionalization, and spin-orbit engineering. Finally, we conclude with the future challenges and opportunities for 2D magnetism.

Ni(NCS)2 monolayer: a robust bipolar magnetic semiconductor

Searching for experimentally feasible intrinsic two-dimensional ferromagnetic semiconductors is of great significance for applications of nanoscale spintronic devices. Here, based on the first-principles calculations, an Ni(NCS)₂ monolayer was systematically investigated. The results showed that the Ni(NCS)₂ monolayer was a robust bipolar ferromagnetic semiconductor with a moderate bandgap of ∼1.5 eV. Based on the Monte Carlo simulation, its Curie temperature was about 37 K. Interestingly, the Ni(NCS)₂ monolayer remains ferromagnetic ordering when strain and electron doping were applied. However, ferromagnetic-to-antiferromagnetic phase transition occurred when high concentrations of holes were doped. Besides, the Ni(NCS)₂ monolayer is confirmed to be potentially exfoliated from its bulk forms due to its small exfoliated energy. Finally, the Ni(NCS)₂ monolayer's thermodynamic, dynamic, and mechanical stabilities were confirmed by the phonon spectrum calculation, ab initio molecular dynamics simulation and elastic constants calculation, respectively. The results showed that the Ni(NCS)₂ monolayer, as a novel 2D ferromagnetic candidate material of new magnetic molecular framework materials, may have a promising potential for magnetic nanoelectronic devices.

Enhancing the Curie temperature of two-dimensional monolayer CrI3 by introducing I-vacancies and interstitial H-atoms

The discovery of two-dimensional monolayer CrI₃ provides a promising possibility for developing spintronic devices. However, the low Curie temperature is an obstacle for practical applications. Here, based on the consideration of the superexchange interaction of ferromagnetic coupling, we investigate the effect of introducing I-vacancies and interstitial H-atoms on the Curie temperature of monolayer CrI₃ by using first-principles calculations and Monte Carlo simulations. Our theoretical conclusions show that the Curie temperature of Cr₈I₂₃ (CrI_2.875), Cr₈I₂₂ (CrI_2.75) and Cr₈I₂₄H (CrI₃H_0.125) significantly increases to 97.0, 82.5 and 112.4 K, respectively. Moreover, the magnetic moment of the Cr atom increases from 3.10 to 3.45 and 3.46μ_B in monolayers Cr₈I₂₃ and Cr₈I₂₂, respectively. We provide more alternative approaches to effectively enhance the Curie temperature of monolayer CrI₃, which will help both theoretical and experimental researchers to directly predict the change in Curie temperature of CrI₃ and its analogs through structural information.

Room temperature spontaneous valley polarization in two-dimensional FeClBr monolayer

The valley degrees of freedom of Bloch electrons provide a proper platform to realize information storage and processing. Using first principles calculations, we propose that the FeClBr monolayer is a ferromagnetic semiconductor with spontaneous valley polarization owing to the combined effect of magnetic exchange interaction and spin-orbit coupling effect. The FeClBr monolayer shows perpendicular magnetic anisotropy, a high Curie temperature of 651 K and a large valley splitting of 188 meV, which are beneficial for the practical applications in valleytronics. Then, the anomalous valley Hall effect can be realized under an in-plane electrical field due to the valley-contrasting berry curvature. According to the optical selectivity rule, the different valleys at K and K^- points in momentum space can be excited by the circularly polarized light in honeycomb structures; however, the FeClBr monolayer can also respond to the linear light. Therefore, the valley degree of freedom of the FeClBr monolayer can be modulated by circularly polarized light, linear light and hole doping. Our work enriches the library of valley materials and provides a candidate for the study of spintronics and valleytronics field.

Ferromagnetic Cr4PtGa17: A Half-Heusler-Type Compound with a Breathing Pyrochlore Lattice

We describe the crystal structure and elementary magnetic properties of a previously unreported ternary intermetallic compound, Cr₄PtGa₁₇, which crystallizes in a rhombohedral unit cell in the noncentrosymmetric space group R3m. The crystal structure is closely related to those of XYZ half-Heusler compounds, where X, Y, and Z are reported to be single elements only, occupying three different face-centered-cubic sublattices. The new material, Cr₄PtGa₁₇, can be most straightforwardly illustrated by writing the formula as (PtGa₂)(Cr₄Ga₁₄)Ga (X = PtGa₂, Y = Cr₄Ga₁₄, Z = Ga); that is, the X and Y sites are occupied by clusters instead of single elements. The magnetic Cr occupies a breathing pyrochlore lattice. Ferromagnetic ordering is found below T_C ∼ 61 K, by both neutron diffraction and magnetometer studies, with a small, saturated moment of ∼0.25 μ_B/Cr observed at 2 K, making Cr₄PtGa₁₇ the first ferromagnetically ordered material with a breathing pyrochlore lattice. A magnetoresistance of ∼140% was observed at 2 K. DFT calculations suggest that the material has a nearly half-metallic electronic structure. The new material, Cr₄PtGa₁₇, the first realization of both a half-Heusler-type structure and a breathing pyrochlore lattice, might pave a new way to achieve novel types of half-Heusler compounds.

CrSbS3 monolayer: a potential phase transition ferromagnetic semiconductor

Two dimensional intrinsic ferromagnetic semiconductors with controllable magnetic phase transition are highly desirable for spintronics. Nevertheless, reports on their successful experimental realization are still rare. Herein, based on first principles calculations, we propose to achieve such a functional material, namely CrSbS₃ monolayer by exfoliating from its bulk crystal. Intrinsic CrSbS₃ monolayer is a ferromagnetic half semiconductor with a moderate bandgap of 1.90 eV. It features an intriguing magnetic phase transition from ferromagnetic to antiferromagnetic when applying a small compressive strain (∼2%), making it ideal for fabricating strain-controlled magnetic switches or memories. In addition, the predicted strong anisotropic absorption of visible light and small effective masses make the CrSbS₃ monolayer promising for optoelectronic applications.

Two-Dimensional Janus FeXY (X, Y = Cl, Br, and I, X ≠ Y) Monolayers: Half-Metallic Ferromagnets with Tunable Magnetic Properties under Strain

Two-dimensional (2D) ferromagnetic materials with high spin polarization are highly desirable for spintronic devices. 2D Janus materials exhibit novel properties due to their broken symmetry. However, the electronic structure and magnetic properties of 2D Janus magnetic materials with high spin polarization are still unclear. Inspired by the successful synthesis of a ferromagnetic FeCl₂ monolayer and 2D Janus MoSSe and WSSe, we systematically study the electronic structure and magnetic properties of Janus FeXY (X, Y = Cl, Br, and I, X ≠ Y) monolayers. Based on the Goodenough-Kanamori-Anderson theory, the ferromagnetism stems from the superexchange interaction mediated by Fe-X/Y-Fe bonds. The band gaps of spin-up channels are large enough (>4 eV) to prevent spin flipping, which is beneficial for spintronic devices. Additionally, the sizable magnetocrystalline anisotropy energy (MAE) indicates that Janus FeXY monolayers are suitable for information storage. More importantly, the half-metallic character is still kept in Janus FeXY monolayers, and their magnetic properties are enhanced by the biaxial compressive strain. The MAE of FeClI and FeBrI increases by 1 order of magnitude, and the Curie temperature of FeXY monolayers enhances by 100%. These results provide an example of the 2D Janus half-metallic materials and enrich the 2D magnetic material library.

Strain modulation of the spin-valley polarization in monolayer manganese chalcogenophosphates alloys

Inspired by the profound physical connotations and potential applications of the spintronics and valleytronics, two-dimensional (2D) monolayer manganese chalcogenophosphates alloys are constructed, and the strain modulated spin-valley characteristics are investigated through the first principles calculations. For both the MnFePS₃and MnFePSe₃, the conductivity can be tuned reversibly between semiconductive and half-metallic, while and magnetic stability is controllable between ferromagnetism and antiferromagnetism. Large valley splitting of up to 1000 meV is achieved in MnFePS₃under a -4% strain. Simultaneous spin splitting of 219 meV and valley splitting of 160 meV are acquired in MnFePS₃under a 4% strain. Strain tunable magnetic moment and interaction between Mn, Fe and S/Se atoms are revealed as the internal mechanisms of controlling the magnetic stability, spin and valley polarizations in the two structures. All the findings in this work provide a strategy for the manipulation of spin and valley degrees of freedom in 2D magnetic materials.