Antiferromagnetic Semiconductor Research Articles

Light-Controlled Ultrafast Magnetic State Transition in Antiferromagnetic-Ferromagnetic van der Waals Heterostructures.

Manipulating spin in antiferromagnetic (AFM) materials has great potential in AFM opto-spintronics. Laser pulses can induce a transient ferromagnetic (FM) state in AFM metallic systems but have never been proven in two-dimensional (2D) AFM semiconductors and related van der Waals (vdW) heterostructures. Herein, using 2D vdW heterostructures of FM MnS2 and AFM MXenes as prototypes, we investigated optically induced interlayer spin transfer dynamics based on real-time time-dependent density functional theory. We observed that laser pulses induce significant spin injection and interfacial atom-mediated spin transfer from MnS2 to Cr2CCl2. In particular, we first demonstrated the transient FM state in semiconducting AFM-FM heterostructures during photoexcited processes. The proximity magnetism breaks the magnetic symmetry of Cr2CCl2 in heterostructures. Our results provide a microscopic understanding of optically controlled interlayer spin dynamics in 2D magnetic heterostructures and open a new way to manipulate magnetic order in 2D materials for ultrafast opto-spintronics.

Two-dimensional transition metal triborides: Monolayers with robust intrinsic magnetism and high spin stability

Two-dimensional materials with intrinsic magnetism have provoked comprehensive attentions due to their potential application in spintronics. In this work, a class of stable transition metal triborides, $\mathrm{TM}{\mathrm{B}}_{3}$ ($\mathrm{TM}=\mathrm{Ti}$, V, Cr, Mn, Fe) with various electronic and magnetic features were predicted by density functional theory. Based on static energy, phonon spectrum, and $ab\phantom{\rule{0.16em}{0ex}}initio$ molecular dynamics simulations, all the $\mathrm{TM}{\mathrm{B}}_{3}$ monolayers have thermal and kinetic stability. Meanwhile, $\mathrm{TM}{\mathrm{B}}_{3}\mathrm{s}$ exhibit mechanical anisotropy reflected by Young's modulus and Poisson's ratio. Moreover, $\mathrm{Ti}{\mathrm{B}}_{3}$ and $\mathrm{Fe}{\mathrm{B}}_{3}$ are robust ferromagnetic metals with the respective Curie temperatures of 248 and 367 K. $\mathrm{Cr}{\mathrm{B}}_{3}$ is antiferromagnetic semiconductor with direct bandgap of 513.6 meV and magnetic transform temperatures of as high as 378 K. Finally, it is predicted that the magnetic properties can be further modulated by exerting external strains. Our results may provide new clues for searching and designing two-dimensional magnetic materials.

Strong Neel Ordering and Luminescence Correlation in a Two‐Dimensional Antiferromagnet

AbstractMagneto‐optical effect has been widely used in light modulation, optical sensing, and information storage. Recently discovered 2D van der Waals layered magnets are considered as promising platforms for investigating novel magneto‐optical phenomena and devices, due to the long‐range magnetic ordering down to atomically thin thickness, rich species, and tunable properties. However, majority 2D antiferromagnets suffer from low luminescence efficiency which hinders their magneto‐optical investigations and applications. This work uncovers strong light‐magnetic ordering interactions in 2D antiferromagnetic MnPS3 using a newly‐emerged near‐infrared photoluminescence (PL) mode far below its intrinsic bandgap. This ingap PL mode shows strong correlation with the Neel ordering and persists down to monolayer thickness. Combining the density‐functional theory (DFT), scanning transmission electron microscopy (STEM), and X‐ray photoelectron spectroscopy (XPS), this work illustrates the origin of the PL mode and its correlation with Neel ordering, which can be attributed to the oxygen ion‐mediated states. Moreover, the PL strength can be further tuned and enhanced using ultraviolet‐ozone (UVO) treatment. The studies offer an effective approach to investigate light‐magnetic ordering interactions in 2D antiferromagnetic semiconductors.

Structural, magnetic, and electronic diversity of VTe2 monolayer

Two-dimensional transition metal dichalcogenides (TMDs) exhibit many novel properties due to dimension, lattice distortion, electron-electron interaction etc. Here, we determine that 1T-VTe2 with space group P3‾m1 is an antiferromagnetic metal by first-principles calculations, and three metastable structures are predicted, i.e., the P21/m and C2/m antiferromagnetic semiconductor phases and P3m1 ferrimagnetic half-metal phase. Besides, the C2/m phase can be transfered to the P3m1 phase by electron doping, while hole doping can induce a transition from C2/m phase to P3‾m1 phase. These transitions could be ascribed to a strong coupling of charge, lattice, and spin degrees of freedom in VTe2. The diverse electronic and magnetic properties of VTe2 provide a good platform for researchers to understand the interactions between spin, charge and lattice.

Gap switching in metal-organic coordination chains

We predict two switchable one-dimensional (1D) spin-polarized semiconductors based on metal-organic coordination chains constructed out of Fe, V, and zwitterionic quinone (ZQ) molecules using first-principle density functional theoretical analysis. The Fe-ZQ coordination chain can be converted from a semiconductor to a half-metal when oxidized by chlorine (Cl). Upon chlorination, the magnetic moment of the Fe-ZQ is increased from 4 μB to 5 μB, per iron atom. In addition, the bimetallic (Fe-ZQ-V-ZQ) ferromagnetic semiconducting coordination chain with a very small energy gap of only 90 meV can be converted to an antiferromagnetic semiconductor with a large gap of more than 1 eV when oxidized by chlorine. Its magnetic moment is found to be 8 μB per heterobimetallic unit (Fe and V) after chlorination, and 7 μB without chlorine. These unique properties, namely a switchable or reversible electronic and magnetic characteristics with a transition between different semiconducting states, make these coordination chains to be highly promising candidates for specific applications as multi-functional switch in nanoelectronics and spintronics.

First-principles study on the magnetic and electronic properties of quadruple perovskite CeCu3Co4O12

We used the first-principles calculations to investigate the magnetic structure and electronic properties of quadruple perovskite CeCu3Co4O12. Our calculations demonstrate that CeCu3Co4O12 is an antiferromagnetic semiconductor, in which the A′-site Cu plays a decisive role in magnetic properties. The chemical combination is proved to be Ce4+Cu2.67+3Co3+4O2-12. The mixed-valence Cu2.67+ at A′-site shows A-type antiferromagnetic coupling, whereas the B-site Co3+ with 3d6 (t2g6eg0) electronic configuration is nonmagnetic in the low-spin state. Moreover, the spin-orbital coupling (SOC) effect does not alter the semiconducting performance of CeCu3Co4O12, although the bandgap is sharply reduced when SOC effect was taken into consideration.

Ultrathin Van der Waals Antiferromagnet CrTe3 for Fabrication of In-Plane CrTe3 /CrTe2 Monolayer Magnetic Heterostructures.

Ultrathin van der Waals (vdW) magnets are heavily pursued for potential applications in developing high-density miniaturized electronic/spintronic devices as well as for topological physics in low-dimensional structures. Despite the rapid advances in ultrathin ferromagnetic vdW magnets, the antiferromagnetic counterparts, as well as the antiferromagnetic junctions, are much less studied owing to the difficulties in both material fabrication and magnetism characterization. Ultrathin CrTe3 layers have been theoretically proposed to be a vdW antiferromagnetic semiconductor with intrinsic intralayer antiferromagnetism. Herein, the epitaxial growth of monolayer (ML) and bilayer CrTe3 on graphite surface is demonstrated. The structure, electronic and magnetic properties of the ML CrTe3 are characterized by combining scanning tunneling microscopy/spectroscopy and non-contact atomic force microscopy and confirmed by density functional theory calculations. The CrTe3 MLs can be further utilized for the fabrication of a lateral heterojunction consisting of ML CrTe2 and ML CrTe3 with an atomically sharp and seamless interface. Since ML CrTe2 is a metallic vdW magnet, such a heterostructure presents the first in-plane magnetic metal-semiconductor heterojunction made of two vdW materials. The successful fabrication of ultrathin antiferromagnetic CrTe3 , as well as the magnetic heterojunction, will stimulate the development of miniaturized antiferromagnetic spintronic devices based on vdW materials.

Two-Dimensional Quaternary Transition Metal Sulfide CrMoA2S6 (A = C, Si, or Ge): A Bipolar Antiferromagnetic Semiconductor with a High Néel Temperature.

Bipolar antiferromagnetic semiconductors (BAFSs) make up a class of spintronic materials, holding great promise for the manipulation of spin-polarized currents simply upon application of a voltage gate, but only a few two-dimensional (2D) BAFSs with a high Néel temperature (TN) have been reported. Here, we report a family of magnetic quaternary MM'A2S6 (M = V, Cr, Mn, or Fe; M' = Nb, Mo, Tc, or Ru; A = C, Si, Ge, or Sn) nanosheets by isovalent alloying layered transitional metal trisulfides (MAS3) based on first-principles calculations. Our results show that 2D CrMoA2S6 (A = C, Si, or Ge) nanosheets are BAFSs with band gaps ranging from 1.89 to 2.23 eV. Among them, 2D CrMoC2S6 has the highest TN of 556 K with robust magnetism against carrier doping and external in-plane strain due to a strong delocalization superexchange interaction between the Cr3+ and Mo3+ cations. This study establishes that CrMoC2S6 is an ideal prototype platform for realizing electric control of spin polarization in 2D materials.

Real-space visualization of short-range antiferromagnetic correlations in a magnetically enhanced thermoelectric

Short-range magnetic correlations can significantly increase the thermopower of magnetic semiconductors, representing a noteworthy development in the decades-long effort to develop high-performance thermoelectric materials. Here, we reveal the nature of the thermopower-enhancing magnetic correlations in the antiferromagnetic semiconductor MnTe. Using magnetic pair distribution function analysis of neutron scattering data, we obtain a detailed, real-space view of robust, nanometer-scale, antiferromagnetic correlations that persist into the paramagnetic phase above the N\'eel temperature $T_{\mathrm{N}}$ = 307 K. The magnetic correlation length in the paramagnetic state is significantly longer along the crystallographic $c$ axis than within the $ab$ plane, pointing to anisotropic magnetic interactions. Ab initio calculations of the spin-spin correlations using density functional theory in the disordered local moment approach reproduce this result with quantitative accuracy. These findings constitute the first real-space picture of short-range spin correlations in a magnetically enhanced thermoelectric and inform future efforts to optimize thermoelectric performance by magnetic means.

XGT (X=Fe, Mn, Cr; G=Ge; T=Te) : A family of two-dimensional ternary intrinsic magnetic materials

Two-dimensional (2D) magnetic materials have attracted tremendous attention in the spintronics and nanoelectronics fields. However, intrinsic and robust 2D magnetism is hard to achieve. Using high-throughput first-principles calculations, herein we have explored 2D ternary compounds of a transition metal $(\mathrm{X}=\mathrm{Fe}, \mathrm{Mn}, \mathrm{Cr})$, Ge, and Te, with diverse stoichiometries and geometric configurations. We screened 34 ferromagnetic and 111 antiferromagnetic XGT monolayer structures, including metals, half-metals, and semiconductors, with high magnetic transition temperatures for practical uses. The coupling strength of ferromagnetism in XGT monolayers is related to the ratio of the transition metal element, while the band gap opening is affected by the occupancy of transition metal $d$ states and the Te content. Therefore, the electronic and magnetic structures of XGT monolayers can be manipulated by their stoichiometries. This work delivers a unique perspective for designing compound functional materials and enriches the family of 2D magnets for technological applications.

Layered TiCl2 Monolayer as an Antiferromagnetic Semiconductor

We report layered TiCl2 monolayer to be a robust antiferromagnetic (AFM) semiconductor by investigating its geometry, stability, electronic and magnetic properties using first-principles calculation and Monte Carlo (MC) simulation. The TiCl2 monolayer exfoliated from layered TiCl2 bulk is verified to be an AFM semiconductor with a relatively wide band gap by spin-polarized density of states and energy band structure calculations. Phonon dispersion and elastic modulus calculations show that the TiCl2 monolayer is dynamically and mechanically stable, respectively. The Néel temperature is evaluated to be 368[Formula: see text]K by MC simulation based on Ising model. Additionally, the band gap, the magnetic moment of a single Ti atom and the Néel temperature can be significantly tuned by applied biaxial strain, but the AFM semiconducting behavior is robust against the applied strains, indicating that the TiCl2 monolayer is a potential candidate for high-speed AFM spintronic applications.

Half-metallicity induced by out-of-plane electric field on phosphorene nanoribbons

Exploring the half-metallic nanostructures with large band gap and high carrier mobility is a crucial solution for developing high-performance spintronic devices. The electric and magnetic properties of monolayer zigzag black-phosphorene nanoribbons (ZBPNRs) with various widths are analyzed by means of the first-principles calculations. Our results show that the magnetic ground state is dependent on the width of the nanoribbons. The ground state of narrow nanoribbons smaller than 8ZBPNRs prefers ferromagnetic order in the same edge but antiferromagnetic order between two opposite edges. In addition, we also calculate the electronic band dispersion, density of states and charge density difference of 8ZBPNRs under the action of out-of-plane electric field. More interesting, the addition of out-of-plane field can modulate antiferromagnetic semiconductor to the half metal by splitting the antiferromagnetic degeneracy. Our results propose a new approach to realize half-metal in phosphorene, which overcomes the drawbacks of graphene/silicene with negligible band gap as well as the transitional metal sulfide (TMS) with low carrier mobility.

Prediction of antiferromagnetic metal-rich chalcogenide monolayers M2X (M = Ti, Zr, Hf and X = S, Se, Te) with high Néel temperature

We predict by first-principles calculations a new kind of binary metal-rich chalcogenide monolayers M2X (M = Ti, Zr, Hf and X = S, Se, Te), anti-structure of transition metal dichalcogenides, and study their stability, electronic structures and magnetic properties. This system is an intrinsic two-dimensional antiferromagnetic semiconductor. The magnetic ground state can be expressed as ferromagnetic ordering in a M atomic layer with antiferromagnetic coupling between two M atomic layers. The intralayer ferromagnetic ordering originates from the intralayer ferromagnetic d-px / py-d super-exchange interaction and the interlayer antiferromagnetism comes from the interlayer d-pz-d antiferromagnetic coupling through chalcogenide elements. The monolayers have large perpendicular magnetic anisotropic energy and can be up to 2000 μeV/cell for Hf2X. The anisotropy energy decreases by one order of magnitude when the metal atom M changes from Hf to Ti. In addition, the calculated Néel temperature can reach or even exceed the room temperature. Our findings suggest that the M2X may have potential application in the fields of spintronics, and will promote further theoretical and experimental study of the compounds with the anti-structure of transition metal dichalcogenides.

Reversible strain-induced magnetic phase transition in a van der Waals magnet.

Mechanical deformation of a crystal can have a profound effect on its physical properties. Notably, even small modifications of bond geometry can completely change the size and sign of magnetic exchange interactions and thus the magnetic ground state. Here we report the strain tuning of the magnetic properties of the A-type layered antiferromagnetic semiconductor CrSBr achieved by designing a strain device that can apply continuous, in situ uniaxial tensile strain to two-dimensional materials, reaching several percent at cryogenic temperatures. Using this apparatus, we realize a reversible strain-induced antiferromagnetic-to-ferromagnetic phase transition at zero magnetic field and strain control of the out-of-plane spin-canting process. First-principles calculations reveal that the tuning of the in-plane lattice constant strongly modifies the interlayer magnetic exchange interaction, which changes sign at the critical strain. Our work creates new opportunities for harnessing the strain control of magnetism and other electronic states in low-dimensional materials and heterostructures.

High-throughput analysis of tetragonal transition metal Xenes.

We report a high-throughput first-principles characterization of the structural, mechanical, electronic, and vibrational properties of tetragonal single-layer transition metal Xenes (t-TMXs). Our calculations revealed 22 dynamically, mechanically and chemically stable structures among the 96 possible free-standing layers present in the t-TMX family. As a fingerprint for their structural identification, we identified four characteristic Raman active phonon modes, namely three in-plane and one out-of-plane optical branches, with various intensities and frequencies depending on the material in question. Spin-polarized electronic calculations demonstrated that anti-ferromagnetic (AFM) metals, ferromagnetic (FM) metals, AFM semiconductors, and non-magnetic semiconductor materials exist within this family, evidencing the potential of t-TMXs for further use in multifunctional heterostructures.

Дважды отрицательные среды на основе антиферромагнитных полупроводников для терагерцевого диапазона частот

The paper presents the results of a theoretical study of the dispersion characteristics of electromagnetic waves (EMW) existing in a transversely magnetized antiferromagnetic (AFM) semiconductor with loss. An AFM semiconductor is an infinite bi-gyrotropic medium, the effective material parameters of which are twice negative in several frequency ranges. It was found that these frequency regions are in the terahertz range and there are four backward EMEs in them, two of which are TE waves, and the other two are TM waves.

Double negative media based on antiferromagnetic semiconductors for the terahertz frequency range

The paper presents the results of a theoretical study of the dispersion characteristics of electromagnetic waves (EMW) existing in a transversely magnetized antiferromagnetic (AFM) semiconductor with loss. An AFM semiconductor is an infinite bi-gyrotropic medium, the effective material parameters of which are twice negative in several frequency ranges. It was found that these frequency bands are in the terahertz range, and there are four backward EMEs in them, two of which are TE waves, and the other two are TM waves. Keywords: left-handed media, antiferromagnets, semiconductors, spin waves.

Two-dimensional heterotriangulene-based manganese organic frameworks: bipolar magnetic and half semiconductors with perpendicular magnetocrystalline anisotropy

Two-dimensional (2D) organic intrinsic magnetic semiconductors have potential applications in low-dimensional organic spintronic devices due to their remarkable physical properties. However, 2D metal-organic frameworks with magnetic and semiconducting properties are rare. In this work, the electronic and magnetic properties of 2D heterotriangulene-based manganese organic frameworks including triphenylamine (TPA) and triphenylborane (TPB) organic ligands with methylene (M), carbonyl (C) or oxygen (O) coordination groups were studied by first-principles calculations. XTPA-Mn (X = M and O) is a bipolar magnetic semiconductor with a large spin-flip band gap. CTPA-Mn and XTPB-Mn (X = M, C and O) are half semiconductors with perpendicular magnetocrystalline anisotropy. The electronic properties of materials ranging from half semiconductors to bipolar magnetic semiconductors appear in CTPA-Mn and XTPB-Mn (X = M and C) at biaxial strains. XTPA-Mn and XTPB-Mn with a frustrated antiferromagnetic configuration are semiconductors with good ductility and stability. These results enrich the diversity of 2D organic intrinsic magnetic semiconductors, which have potential applications in spintronic devices.

Hydrogen-Intercalated 2D Magnetic Bilayer: Controlled Magnetic Phase Transition and Half-Metallicity via Ferroelectric Switching.

Electrically controlled magnetism in two-dimensional (2D) multiferroics is highly desirable for both fundamental research and the future development of low-power nanodevices. Herein, inspired by the recently experimentally realized 2D antiferromagnetic MnPSe3 [ Nat. Nanotechnol. 2021, 16 (7), 782] and guided by a heteromagnetic structural design, we engineer strong magnetoelectric coupling in a hydrogen-intercalated 2D MnPSe3 bilayer. Hydrogen functionalization breaks the centrosymmetry of bilayer MnPSe3, leading to out-of-plane ferroelectricity. Moreover, there is a phase transition from antiferromagnetic semiconductor to ferromagnetic half-metal in the H-bonded MnPSe3 layer, while the other remains antiferromagnetic and semiconducting. When reversing the electrical polarization, the intercalated H atom can flip between the top and bottom layers with an ultralow switching barrier, which allows one to tune the magnetic order and conductivity of the individual layers via an external electric field. Our results pave a new avenue to realize strong magnetoelectric coupling in single-phase multiferroic material. The ferroelectricity-controlled magnetic phase transition and half-metallicity offer promising applications in nanoscale spintronics such as electrically written and magnetically read memories.

Femtosecond phononic coupling to both spins and charges in a room-temperature antiferromagnetic semiconductor

Spintronics is postulated on the possibility to employ the magnetic degree of freedom of electrons for computation and couple it to charges. In this view, the combination of the high-frequency of spin manipulations offered by antiferromagnets, with the wide tunability of the electronic properties peculiar of semiconductors provides a promising and intriguing platform. Here we explore this scenario in $\alpha$-MnTe, which is a semiconductor antiferromagnetically ordered at room temperature. Relying on a Raman mechanism and femtosecond laser pulses, we drive degenerate modes of coherent optical phonons, which modulate the chemical bonds involved in the super-exchange interaction. The spectrally-resolved measurements of the transient reflectivity reveal a coherent modulation of the band-gap at the frequency of 5.3 THz. The detection of the rotation of the polarisation, typically associated with magneto-optical effects, shows coherent and incoherent contributions. Modelling how the ionic motion induced by the phonons affects the exchange interaction in the material, we calculate the photoinduced THz spin dynamics: the results predict both a coherent and incoherent response, the latter of which is consistent with the experimental observation. Our work demonstrates that the same phonon modes modulate both the charge and magnetic degree of freedom, suggesting the resonant pumping of phonons as a viable way to link spin and charge dynamics even in nonlinear regimes.