Exploring two-dimensional (2D) materials with magnetic ordering is a focus of current research. It remains a challenge to achieve tunable magnetism in a material of one-atom-thickness without introducing extrinsic magnetic atoms or defects. Here, based on first-principles calculations, we propose that tunable ferromagnetism can be realized in the recently synthesized holey 2D C$_2$N ($h$2D-C$_2$N) monolayer via purely electron doping that can be readily achieved by gating. We show that owing to the prominent van Hove singularity in the band structure, the material exhibits ferromagnetism even at a small doping level. Remarkably, over a wide doping range of 4$\times$10$^{13}$/cm$^2$ to 8$\times$10$^{13}$/cm$^2$, the system becomes half-metallic, with carriers fully spin-polarized. The estimated Curie temperature can be up to 320 K. Besides gating, we find that the magnetism can also be effectively tuned by lattice strain. Our result identifies $h$2D-C$_2$N as the first material with single-atom-thickness that can host gate-tunable room-temperature half-metallic magnetism, suggesting it as a promising platform to explore nanoscale magnetism and flexible spintronic devices.
Motivated by a recent experiment that reported the synthesis of a new 2D material nitrogenated holey graphene (C$_2$N) [Mahmood \textit{et al., Nat. Comm.}, 2015, \textbf{6}, 6486], electronic, magnetic, and mechanical properties of nitrogenated (C$_2$N), phosphorated (C$_2$P) and arsenicated (C$_2$As) monolayer holey graphene structures are investigated using first-principles calculations. Our total energy calculations indicate that, similar to the C$_2$N monolayer, the formation of the other two holey structures are also energetically feasible. Calculated cohesive energies for each monolayer…
A new two-dimensional material, the C$_2$N holey 2D (C$_2$N-$h$2D) crystal, has recently been synthesized. Here we investigate the strain effects on the properties of this new material by first-principles calculations. We show that the material is quite soft with a small stiffness constant and can sustain large strains $\geq 12\%$. It remains a direct gap semiconductor under strain and the bandgap size can be tuned in a wide range as large as 1 eV. Interestingly, for biaxial strain, a band crossing effect occurs at the valence band maximum close to a 8\% strain, leading to a dramatic increase …
The strain-induced magnetism is observed in single-layer MoS2 with atomic single vacancies from density functional calculations. Calculated magnetic moment is no less than 2muB per vacancy defect. The straininduced band gap closure is concurrent with the occurrence of the magnetism. Possible physical mechanism of the emergence of strain-induced magnetism is illustrated. We also demonstrate the possibility to test the predicted magnetism in experiment. Our study may provide an opportunity for the design of new type of memory-switching or logic devices by using earth-rich nonmagnetic materials M…
The effects of strain and hydrogenation on the electronic and magnetic properties of monolayers of Ta based dichalcogenides (TaX2; X = S, Se, Te) are investigated using density-functional theo-ry. We predict a complex scenario of strain-dependent magnetic phase transitions involving par-amagnetic, ferromagnetic, and modulated antiferromagnetic states. Covering one of the two chalcogenide surfaces with hydrogen switches the antiferromagnetic/nonmagnetic TaX2 mono-layers to a semiconductor. Our research opens new pathways towards the manipulation of mag-netic properties for future optoelectronic…
The realization of multiferroicity in 2D nanomaterials is crucially important for designing advanced nanoelectronic devices such as non-volatile multistate data storage. In this work, the coexistence of ferromagnetism and ferroelectricity is reported in monolayer SnTe system by transition metal (TM) doping. Based on first-principles calculations, the spontaneous spin polarization could be realized by TM doping in ferroelectric SnTe monolayer. In addition to in-plane ferroelectric polarization, the out-of-plane ferroelectric polarization emerges in Mn (Fe)-doped SnTe monolayer due to the intern…
Using first-principles calculations, we demonstrate that an Fe monolayer can assume very different magnetic phases on hexagonal hcp (0001) and fcc (111) surfaces of 4d- and 5d-transition metals. Due to the substrates' d-band filling, the nearest-neighbor exchange coupling of Fe changes gradually from antiferromagnetic (AFM) for Fe films on Tc, Re, Ru and Os to ferromagnetic on Rh, Ir, Pd, and Pt. In combination with the topological frustration on the triangular lattice of these surfaces the AFM coupling results in a 120-degree Neel structure for Fe on Re and Ru and an unexpected double-row-wis…
We have studied the electronic, magnetic and linear phonon dispersion behavior of Phosphorene monolayer using rst principle based ab initio method. Phosphorene monolayer is a semiconducting system with a dimensional dependent variable range of band gap. Vacancy has been done to study the geometry and physical behavior of the monolayer system. Pristine, vacancy induced monolayer and vacancy induced doped monolayer are included in the calculation. Dopant concentration has been well checked via optimization algorithm to maintain the dilute magnetic semiconducting behavior of the monolayer system.…
Two-dimensional transition metal dichalcogenides have attracted great attention recently. Motivated by a recent study of crystalline bulk VTe$_2$, we theoretically investigated the spin-charge-lattice interplay in monolayer VTe$_2$. To understand the controversial experimental reports on several different charge density wave ground states, we paid special attention to the 'hidden' role of antiferromagnetism as its direct experimental detection may be challenging. Our first-principles calculations show that the 4$\times$1 charge density wave and the corresponding lattice deformation are accompa…
Two-dimensional van der Waals (2D vdW) materials that display ferromagnetism and piezoelectricity have received increased attention. Despite numerous 2D materials have so far been reported as ferromagnetic, developing an air stable and transferable vdW material that is multiferroic has been challenging. To address this problem, we report our work on layered transition metal silicates that are derivatives of kaolinites and lizardites with transition metal substituting on Al$^{3+}$ and Mg$^{2+}$ sites using ab-initio calculations. Using Density Functional Theory (DFT), we show that these compoun…
Magnetisms in $p$-type monolayer GaX (X=S,Se) is investigated by performing density-functional calculations. Due to the large density of states near the valence band edge, these monolayer semiconductors are ferromagnetic within a small range of hole doping. The intrinsic Ga vacancies can promote local magnetic moment while Se vacancies cannot. Magnetic coupling between vacancy-induced local moments is ferromagnetic and surprisingly long-range. The results indicate that magnetization can be induced by hole doping and can be tuned by controlled defect generation.
Two dimensional magnetic materials, with tunable electronic properties could lead to new spintronic, magnetic and magneto-optic applications. Here, we explore intrinsic magnetic ordering in two dimensional monolayers of transition metal tri-halides (MX$_3$, M = V, Cr, Mn, Fe and Ni, and X = F, Cl, Br and I), using density functional theory. We find that other than FeX$_3$ family which has an anti-ferromagnetic ground state, rest of the trihalides are ferromagnetic. Amongst these the VX$_3$ and NiX$_3$ family are found to have the highest magnetic transition temperature, beyond the room tempera…
When combined with transition metals with partially filled $d$-orbitals, magnetism can be incorporated in two-dimensional materials, which greatly expands the scope for fundamental researches and potential applications of these materials. Here, a first-principles study of a new two-dimensional ferromagnet VI$_3$ has been carried out. The structural symmetry, magnetic and electronic properties of VI$_3$ in its bulk and single layer forms have been confirmed and predicted, respectively. Its ferromagnetic Curie temperature is predicted to be reduced by half in its monolayer form. In addition, the…
Using first-principles calculations, we study the magnetic properties of a Co monolayer on a Pt(111) surface with a capping monolayer of selected $5d$ elements (Re, Os, Ir, Pt and Au). First we determine the tensorial exchange interactions and magnetic anisotropies characterizing the Co monolayer for all considered systems. We find a close relationship between the magnetic moment of the Co atoms and the nearest-neighbor isotropic exchange interaction, which is attributed to the electronic hybridization between the Co and the capping layers, in spirit of the Stoner picture of ferromagnetism. Th…
Giant magnetization of polyalanine monolayers on gold observed in resent years along with unusual large spin selectivity, the potential of the film and its temperature dependence are all explained in the context of vacuum polarization at the gold-monolayer interface. The enhancement is directly related to the fine structure constant, and involves a change in basic physical parameters including changes in the permeability of the vacuum and in the local zero point energy of the gold monolayer interface. Formation of an ordered state by the self-assembly process and the interaction of the monolay…
A systematic ab initio study is performed for the spin and orbital moments and for the validity of the sum rules for x-ray magnetic circular dichroism for Fe systems with various dimensionality (bulk, Pt-supported monolayers and monatomic wires, free-standing monolayers and monatomic wires). Qualitatively, the results are similar to those for the respective Co systems, with the main difference that for the monatomic Fe wires the <Tz> term in the spin sum rule is much larger than for the Co wires. The spin and orbital moments induced in the Pt substrate are also discussed.
Emergence of half-semiconductor behavior and tunable magnetism via carrier doping in Janus VXSe (X=Cl, Br, I) monolayers
Southwest University（西南大学）；Hanhong College, Southwest University（汉弘学院，西南大学）；AECC Hunan Aviation Powerplant Research Institute（中国航发湖南航空发动机研究所）；Chengdu University of Technology（成都理工大学）；Leshan Normal University（乐山师范学院）；Shanghai Jiao Tong University（上海交通大学）
Designing two-dimensional (2D) materials with magnetic and topological properties has continuously attracted intense interest in fundamental science and potential applications. Here, on the basis of first-principles calculations, we predict the coexistence of antiferromagnetism and Dirac nodal loop (NL) in the monolayer MnB, where the band crossing points are very close to the Fermi Level. Remarkably, a moderate strain can induce an antiferromagnetic to ferromagnetic phase transition, driving the monolayer MnB to a ferromagnetic metal with Weyl NLs. Such a type of topological quantum phase tra…
Two-dimensional (2D) materials with robust magnetism have drawn immense attention for their promising applications in spintronics. Recently, intrinsic ferromagnetic vanadium triiodide (VI3) has been synthesized experimentally. To enhance its spintronic property, we modified VI3 by interstitial doping with 3d transition metals (TM) and used first-principles calculations to investigate the geometric structure, formation energy, electronic property, and magnetism of pristine VI3 and 3d TM-doped VI3 monolayer. Among eight transition metal (Sc-, Ti-, V-, Cr-, Mn-, Fe-, Co-, and Ni-) doped VI3 mater…
Emergent gold-induced interfacial magnetism in monolayer FePS$_3$
European Synchrotron Radiation Facility（欧洲同步辐射装置）；Université Grenoble Alpes, CNRS, Grenoble INP, Institut NEEL（格勒诺布尔阿尔卑斯大学、法国国家科学研究中心、格勒诺布尔理工学院、NEEL研究所）；Department of Physics Giuseppe Occhialini, University of Milano-Bicocca（米兰比可卡大学朱塞佩·奥基亚利尼物理系）；Université Grenoble Alpes, CEA, IRIG, MEM（格勒诺布尔阿尔卑斯大学、法国原子能和替代能源委员会、研究与信息技术部、材料与物理化学实验室）
Two-dimensional materials and their heterostructures have opened up new possibilities for magnetism at the nanoscale. In this study, we utilize first-principles simulations to investigate the structural, electronic, and magnetic properties of $\textrm{Fe}/\textrm{WSe}_2/\textrm{Pt}$ systems containing pristine, defective, or doped $\textrm{WSe}_2$ monolayers. The proximity effects of the ferromagnetic Fe layer are studied by considering defective and vanadium-doped $\textrm{WSe}_2$ monolayers. All heterostructures are found to be ferromagnetic, and the insertion of the transition-metal dichalc…
Two-dimensional (2D) magnetic materials hosting nontrivial topological states are interesting for fundamental research as well as practical applications. Recently, the topological state of 2D Weyl half-semimetal (WHS) was proposed, which hosts fully spin polarized Weyl points robust against spin-orbit coupling in a 2D ferromagnetic system, and single-layer PtCl$_3$ was predicted as a platform for realizing this state. Here, we perform an extensive search of 2D PtCl$_3$ structures, by using the particle swarm optimization technique and density functional theory calculation. We show that the des…
We find, through first-principles calculations, that hole doping induces a ferromagnetic phase transition in monolayer GaSe. Upon increasing hole density, the average spin magnetic moment per carrier increases and reaches a plateau near 1.0 $μ_{\rm{B}}$/carrier in a range of $3\times 10^{13}$/cm$^{2}$-$1\times 10^{14}$/cm$^{2}$ with the system in a half-metal state before the moment starts to descend abruptly. The predicted magnetism originates from an exchange splitting of electronic states at the top of the valence band where the density of states exhibits a sharp van Hove singularity in thi…
First-Principles Study of Two-Dimensional CeN: Interplay between Structural Stability, Electronic Structure, and Magnetism
Instituto de Física “Ing. Luis Rivera Terrazas”, Benemérita Universidad Autónoma de Puebla（普埃布拉自治大学路易斯·里韦拉·特拉亚斯物理研究所）；Facultad de Ingeniería, Benemérita Universidad Autónoma de Puebla（普埃布拉自治大学工程学院）
Next-generation spintronic devices will benefit from low-dimensionality, ferromagnetism, and half-metallicity, possibly controlled by electric fields. We find these technologically-appealing features to be combined with an exotic microscopic origin of magnetism in doped CdOHCl, a van der Waals material from which 2D layers may be exfoliated. By means of first principles simulations, we predict homogeneous hole-doping to give rise to $p$-band magnetism in both the bulk and monolayer phases and interpret our findings in terms of Stoner instability: as the Fermi level is tuned via hole-doping thr…
The discovery of monolayer graphene has initiated two fertile fields in modern condensed matter physics, Dirac semimetals and atomically-thin layered materials. When these trends meet again in transition metal compounds, which possess spin and orbital degrees of freedom and strong electron correlations, more exotic phenomena are expected to emerge in the cross section of topological states of matter and Mott physics. Here, we show by using ab initio calculations that a monolayer form of transition metal trichalcogenides (TMTs), which has a honeycomb network of transition metal cations, may exh…
The atomic thickness of two-dimensional (2D) materials provides a unique opportunity to control material properties and engineer new functionalities by electrostatic doping. Electrostatic doping has been demonstrated to tune the electrical and optical properties of 2D materials in a wide range, as well as to drive the electronic phase transitions. The recent discovery of atomically thin magnetic insulators has opened up the prospect of electrical control of magnetism and new devices with unprecedented performance. Here we demonstrate control of the magnetic properties of monolayer and bilayer …
Graphene-based materials have been suggested for applications ranging from nanoelectronics to nanobiotechnology. However, the realization of graphene-based technologies will require large quantities of free-standing two-dimensional (2D) carbon materials with tuneable physical and chemical properties. Bottom-up approaches via molecular self-assembly have great potential to fulfil this demand. Here, we report on the fabrication and characterization of graphene made by electron-radiation induced cross-linking of aromatic self-assembled monolayers (SAMs) and their subsequent annealing. In this pro…
Recent studies on superconductivity in NbSe$_2$ have demonstrated a large anisotropy in the superconducting critical field when the material is reduced to a single monolayer. Motivated by this recent discovery, we use density functional theory (DFT) calculations to quantitatively address the superconducting properties of bulk and monolayer NbSe$_2$. We demonstrate that NbSe$_2$ is close to a ferromagnetic instability, and analyze our results in the context of experimental measurements of the spin susceptibility in NbSe$_2$. We show how this magnetic instability, which is pronounced in a single…
Two-dimensional electron gas due to semiconductor interfaces can have high mobility and exhibits superconductivity, magnetism, and other exotic properties that are unexpected in constituent bulk materials. We study crystal structures, electronic states, and magnetism of short-period (BTO)$_m$/(GTO)$_2$ ($m$=2 and 4) superlattices consisting of ferroelectric BaTiO$_3$ (BTO) and ferrimagnetic insulating polar GdTiO$_3$ (GTO) by first principles calculations. Our investigation shows that the middle Ti-O monolayer in the GTO layer becomes metallic because the ferroelectricity in the insulating BTO…
Magnetic two-dimensional (2D) materials have received tremendous attention recently due to its potential application in spintronics and other magnetism related fields. To our knowledge, five kinds of 2D materials with intrinsic magnetism have been synthesized in experiment. They are CrI3, Cr2Ge2Te6, FePS3, Fe3GeTe2 and VSe2. Apart from the above intrinsic magnetic 2D materials, many strategies have also been proposed to induce magnetism in normal 2D materials such as atomic modification, spin valve and proximity effect. Various devices have also been designed to fulfill the basic functions of …
We examine the adsorption of a single Ni atom on a monolayer of MgO on a Ag substrate using DFT and DFT+U computational approaches. We find that the electronic and magnetic properties vary considerably across the three binding sites of the surface. Two of the binding sites are competitive in energy, and the preferred site depends on the strength of the on-site Coulomb interaction U. These results can be understood in terms of the competition between bonding and magnetism for surface adsorbed transition metal atoms. Comparisons are made with a recent experimental and theoretical study of Co on …
Two-dimensional (2D) palladium ditelluride (PdTe2) and platinum ditelluride (PtTe2) are two Dirac semimetals which demonstrate fascinating quantum properties such as superconductivity, magnetism and topological order, illustrating promising applications in future nanoelectronics and optoelectronics. However, the synthesis of their monolayers is dramatically hindered by strong interlayer coupling and orbital hybridization. In this study, an efficient synthesis method for monolayer PdTe2 and PtTe2 is demonstrated. Taking advantages of the surface reaction, epitaxial growth of large-area and high…
Controlling magnetism and electronic properties of two-dimensional (2D) materials by purely electrical means is crucial and highly sought for high-efficiency spintronics devices since electric field can be easily applied locally compared with magnetic field. The recently discover 2D Janus crystals has provide a new platform for nanoscale electronics and spintronics due to their broken inversion symmetry nature. The intrinsic ferromagnetic Jauns monolayer, and hence the tunable physical properties, is therefore of great interest. Here, through comprehensive density functional theory calculation…
Flat band moiré superlattices have recently emerged as unique platforms for investigating the interplay between strong electronic correlations, nontrivial band topology, and multiple isospin 'flavor' symmetries. Twisted monolayer-bilayer graphene (tMBG) is an especially rich system owing to its low crystal symmetry and the tunability of its bandwidth and topology with an external electric field. Here, we find that orbital magnetism is abundant within the correlated phase diagram of tMBG, giving rise to the anomalous Hall effect (AHE) in correlated metallic states nearby most odd integer fillin…
Doping a two-dimensional semiconductor with magnetic atoms is a possible route to induce magnetism in the material. We report on the atomic structure and electronic properties of monolayer WSe$_2$ intentionally doped with vanadium atoms by means of scanning transmission electron microscopy and scanning tunneling microscopy and spectroscopy. Most of the V atoms incorporate at W sites. These V$_W$ dopants are negatively charged, which induces a localized bound state located 140 meV above the valence band maximum. The overlap of the electronic potential of two charged V$_W$ dopants generates addi…
We use density-functional theory to describe the initial stages of Fe film growth on GaAs(001), focusing on the interplay between chemistry and magnetism at the interface. Four features appear to be generic: (1) At submonolayer coverages, a strong chemical interaction between Fe and substrate atoms leads to substitutional adsorption and intermixing. (2) For films of several monolayers and more, atomically abrupt interfaces are energetically favored. (3) For Fe films over a range of thicknesses, both Ga- and As-adlayers dramatically reduce the formation energies of the films, suggesting a surfa…
A description of non-collinear magnetism in the framework of spin-density functional theory is presented for the exact exchange energy functional which depends explicitly on two-component spinor orbitals. The equations for the effective Kohn-Sham scalar potential and magnetic field are derived within the optimized effective potential (OEP) framework. With the example of a magnetically frustrated Cr monolayer it is shown that the resulting magnetization density exhibits much more non-collinear structure than standard calculations. Furthermore, a time-dependent generalization of the non-collinea…
Recently intrinsic ferromagnetism in two-dimensional(2D) van der Waals materials was discovered [1, 2, 3]. A monolayer of Chromiun triiodide(CrI3) is ferromagnetic while a bilayer structure was reported to be anti-ferro magnetic, moreover an external electric field changes its magnetic phase [4]. We have studied the two found in nature stackings of CrI3 bilayers and found that indeed the magnetic phase of one of them can be tuned by an external electric field while the other remains ferromagnetic. We simulate those results with ab initio calculations and explain them with a simple model based …
The epitaxial system Sm/Co(0001) was studied for Sm coverages up to 1 monolayer (ML) on top of ultrathin Co/W(110) epitaxial films. Two ordered phases were found for 1/3 and 1 ML Sm, respectively. The valence state of Sm was determined by means of photoemission and magnetic properties were measured by magneto-optical Kerr effect. We find that 1 ML Sm causes a strong increase of the coercivity with respect to that of the underlying 10 ML Co film. Element-specific hysteresis loops, measured by using resonant soft x-ray reflectivity, show the same magnetic behaviour for the two elements.
The discovery of monolayer MA$_2$Z$_4$ (M = transition metals; A = IVA elements; Z = VA elements, Science 369, 2020, 670-674) family has led another advance for facilitating and harnessing magnetism in low-dimensional materials. However, only Cr and V based MA$_2$N$_4$ compounds exhibit intrinsic magnetism yet with unsatisfied magnetic ordering temperature. Herein, we identify a stable ferromagnetic number of this family, i.e., VGe$_2$Z$_4$ monolayer, by means of first-principles calculations. It is found that the magnetic configuration sustains under both compression and tensile uniaxial in-p…
The discovery of archetypal two-dimensional (2D) materials provides enormous opportunities in both fundamental breakthroughs and device applications, as evident by the research booming in graphene, atomically thin transition-metal chalcogenides, and few-layer black phosphorous in the past decade. Here, we report a new, large family of semiconducting dialkali-metal monochalcogenides (DMMCs) with an inherent A$_{2}$X monolayer structure, in which two alkali sub-monolayers form hexagonal close packing and sandwich the triangular chalcogen atomic plane. Such unique lattice structure leads to extra…
A combined experimental, using X-ray Magnetic Circular Dichroism and theoretical investigation, using full-potential Korringa-Kohn-Rostoker (KKR) Green function method, is carried out to study the spin structure of small magnetic Cr adatom--clusters on the surface of 3 monolayers of $fcc$ Fe deposited on Cu(001). The exchange interaction between the different Cr adatoms as well as between the Cr atoms and the Fe atoms is of antiferromagnetic nature and of comparable magnitude, leading due to frustration to complex non-collinear magnetic configurations. The presence of non-collinear magnetic co…
Recent experimental discoveries of two-dimensional (2D) magnets have triggered intense research activities to search for atomically thin magnetic systems. Using first-principles calculations, we predict the emergence of 2D magnetism in the monolayers (MLs), few layers, and surfaces of nonmagnetic layered electrides Hf2X (X = S, Se, Te) consisting of three-atom-thick Hf-X-Hf stacks. It is revealed that each bulk Hf2X hosts a novel quantum state of Dirac nodal lines with a high density of states arising from Hf-5d cationic and interlayer anionic electrons around -0.9 eV below the Fermi level EF.…
