Antiferromagnetic Research Articles

Controllable half-metallicity in MnPX3 monolayer

Modulable electronic and magnetic structures significantly extend the properties and applications of two-dimensional (2D) materials. 2D antiferromagnets (AFM) can even become ferromagnets (FM) by various approaches, which ignites growing research interests in 2D AFM. Through first-principles calculations, we find that the adsorption of Li (electron doping) and F (hole doping) on the surface of MnPSe3 can induce half-metallicity with opposite spin polarizations. The adsorption site, concentration, charge transfer, and the exchange energy are investigated in detail, indicating the robustness of half-metallicity. At the interface of MnPS3/Au(111) heterostructure, we find electrons transfer from Au(111) to MnPS3, forming the Ohmic contact and inducing AFM-FM transition. All our results show that ferromagnetic MnPX3 (X = S and Se) monolayer with half-metallicity can be easily obtained, which may be of great significance in 2D spintronic materials and devices.

Designing van der Waals layers for ferromagnetic quantum spin Hall phase

Most theoretically predicted and experimentally confirmed quantum spin Hall effects (QSHEs) are limited to zero-moment magnets. In this study, we theoretically anticipate the QSHE in ferromagnets and the quantum anomalous Hall effect (QAHE) in antiferromagnets through van der Waals stacked layers, where the magnetization direction is confined to the in-plane. We introduce a search rule for constructing ferromagnetic (FM) quantum spin Hall insulator (QSHI) and antiferromagnetic (AFM) quantum anomalous Hall insulator (QAHI) and further predict a real material of the LuN2/GaS/LuN2 van der Waals multilayer by first-principles calculations. Our results demonstrate the superposition and elimination of Chern numbers under mirror symmetry and time-reversal symmetry, and they further indicate that FM QSHI and AFM QAHI can be converted through deflection magnetization. These findings broaden the material class for QSHE and QAHE and propose a scheme for constructing FM QSHI and AFM QAHI.

First-Principles Prediction of Structural Distortions in the Cuprates and Their Impact on the Electronic Structure

Materials-realistic microscopic theoretical descriptions of copper-based superconductors are challenging due to their complex crystal structures combined with strong electron interactions. Here, we demonstrate how density functional theory can accurately describe key structural, electronic, and magnetic properties of the normal state of the prototypical cuprate Bi2Sr2CaCu2O8+x (Bi-2212). We emphasize the importance of accounting for energy-lowering structural distortions, which then allows us to (a) accurately describe the insulating antiferromagnetic (AFM) ground state of the undoped parent compound (in contrast to the metallic state predicted by previous studies); (b) identify numerous low-energy competing spin and charge stripe orders in the hole-overdoped material nearly degenerate in energy with the AFM ordered state, indicating strong spin fluctuations; (c) predict the lowest-energy hole-doped crystal structure including its long-range structural distortions and oxygen dopant positions that match high-resolution scanning transmission electron microscopy measurements; and (d) describe electronic bands near the Fermi energy with flat antinodal dispersions and Fermi surfaces that are in agreement with angle-resolved photoemission spectroscopy (ARPES) measurements and provide a clear explanation for the structural origins of the so-called “shadow bands.” We also show how one must go beyond band theory and include fully dynamic spin fluctuations via a many-body approach when aiming to make quantitative predictions to measure the ARPES spectra in the overdoped material. Finally, regarding spatial inhomogeneity, we show that the local structure at the CuO2 layer, rather than dopant electrostatic effects, modulates the local charge-transfer gaps, local correlation strengths, and by extension the local superconducting gaps. Published by the American Physical Society 2024

Supramolecular Rotor Assembly for the Design of a Hybrid Ferroelectric‐Antiferromagnetic Multiferroic Semiconductor

Ferroelectric (FE)‐antiferromagnetic (AFM) multiferroic materials have sparked growing interest due to their huge possibilities in energy‐saving, photoelectric devices, nonvolatile storage, and switches. However, realizing FE‐AFM properties in a hybrid molecular material is difficult because ferroelectric and magnetic orders are commonly mutually exclusive. Here, we report an FE‐AFM multiferroic semiconductor [NH4(18‐crown‐6)]2[Mn(SCN)4] (NCMS) by supramolecular assembly approach via molecular rotor synthon [NH4(18‐crown‐6)] and inorganic magnetic module [Mn(SCN)4]. Interestingly, NCMS shows good ferroelectricity with a spontaneous polarization (Ps) of 5.94 μC cm−2 higher than most crown‐ether‐based ferroelectrics. Especially, the realization of antiferromagnetism is for the first time in the crown ether hybrid perovskite ferroic systems. Additionally, semiconductor NCMS displays an X‐ray radiation detection response with a large photo/dark current on‐off ratio (197). Our study not only gives a deep insight into understanding multiferroic properties but also provides a novel and efficient approach to realizing high‐performance hybrid multiferroic materials.

Supramolecular Rotor Assembly for the Design of a Hybrid Ferroelectric-Antiferromagnetic Multiferroic Semiconductor.

Ferroelectric (FE)-antiferromagnetic (AFM) multiferroic materials have sparked growing interest due to their huge possibilities in energy-saving, photoelectric devices, nonvolatile storage, and switches. However, realizing FE-AFM properties in a hybrid molecular material is difficult because ferroelectric and magnetic orders are commonly mutually exclusive. Here, we report an FE-AFM multiferroic semiconductor [NH4(18-crown-6)]2[Mn(SCN)4] (NCMS) by supramolecular assembly approach via molecular rotor synthon [NH4(18-crown-6)] and inorganic magnetic module [Mn(SCN)4]. Interestingly, NCMS shows good ferroelectricity with a spontaneous polarization (Ps) of 5.94 μC cm-2 higher than most crown-ether-based ferroelectrics. Especially, the realization of antiferromagnetism is for the first time in the crown ether hybrid perovskite ferroic systems. Additionally, semiconductor NCMS displays an X-ray radiation detection response with a large photo/dark current on-off ratio (197). Our study not only gives a deep insight into understanding multiferroic properties but also provides a novel and efficient approach to realizing high-performance hybrid multiferroic materials.

Advancing sustainable ammonia synthesis with the magnetic La-doped Ti3C2O2 MXenes

Developing an easy ammonia (NH3) production method to circumvent the demanding conditions of the Haber-Bosch process is a significant stride towards self-sufficiency in NH3 production and environment preservation. In pursuit of this goal, we carried out a theoretical approach to investigate the electrocatalytic N2 reduction reaction (eN2RR) using the magnetic La-doped Ti3C2O2 (La-Ti3C2O2) MXene electrocatalyst. The first principle calculations of the DFT, conducted using the Vienna Ab-Initio Storage Package (VASP) were instrumental in assessing the performance of ferromagnetic (FM) and antiferromagnetic (AFM) configurations of La-Ti3C2O2. While Ti3C2O2 reveals limitations in eN2RR efficiency attributed to its suboptimal surface reactivity, both FM and AFM structures of La-Ti3C2O2 exhibit enhanced electronic properties, enabling improved electron transfer features. La-Ti3C2O2 demonstrates heightened N2 adsorption capabilities and reduced energy barriers for transitional species towards NH3 production, presenting superior performance to Ti3C2O2. The density of states (DOS) analysis of La-Ti3C2O2 provided outcomes supporting the AFM as the credible magnetic configuration, a statement reinforced by the superior N2 conversion performance in the AFM structure compared to FM. During this process of eN2RR, a study focused on the favorable pathway with less energy consumption is directed.

Effects of Lu-doping on the magnetic behaviour and ordering of (Ho[formula omitted]Lu[formula omitted])2Fe2Si2C

We have investigated the effects of Lu substitution on the magnetic behaviour and ordering of (Ho1−xLux)2Fe2Si2C (x = 0.32 and 0.46) by high-resolution neutron powder diffraction, magnetisation and specific heat over the temperature range 2 to 300 K. Our study has establised that the antiferromagnetic (AFM) state is weakened upon Lu substitution and that the Néel temperature TN shifts towards lower temperature with increasing Lu content. The replacement of the magnetic Ho3+ ion by the non-magnetic Lu3+ ion of smaller atomic radius, leads to a modification of the crystal field levels, as indicated by the specific heat measurements. Neutron diffraction data analysis reveals that the magnetic structure of undoped Ho2Fe2Si2C, which exhibits a commensurate, antiferromagnetic ordering of the Ho sublattice along the b-axis with a propagation vector k = [0, 0, 12], is maintained in the Lu-doped (Ho1−xLux)2Fe2Si2C compounds.

Study of the magnetoelastic phase transition in near equiatomic FeRh alloys through T-FORC analysis and neutron diffraction

Fe100-xRhx alloys with x ∼ 50 undergo a first-order magnetoelastic phase transition close to room temperature from the low-temperature antiferromagnetic (AFM) to the high-temperature ferromagnetic (FM) state. For Fe50Rh50, the AFM-FM-AFM transitions may occur involving various coexistent mechanisms. Although the Fe49Rh51 composition closely resembles the equiatomic counterpart, its first-order phase transition exhibits notable disparities, whose underlying process remains unexplained. We combined neutron thermo-diffraction and magnetization measurements to study the phase transformation in the two alloys. The Kolmogorov-Johnson-Mehl-Avrami (KJMA) model and temperature first-order reversal curve (T-FORC) analysis are applied to explore this matter. The techniques were applied to both alloys, Fe50Rh50 and Fe49Rh51, to use the former as reference to emphasize the distinct characteristics of the latter. The study highlights the defect-based growth hindering in Fe50Rh50 and the almost complete absence of it in Fe49Rh51, accompanied by a significant effect of the FM phase magnetostatic field. This work presents a new way to obtain detailed information from the T-FORCs by analyzing their T-derivative curves. This method indicates that the superposition of applied and magnetostatic fields causes the notable differences observed in alloys with such close atomic composition. It reveals and explains peculiar features of the Fe49Rh51 temperature-driven transition, such as the anomalous cross-over of the first-order reversal magnetization curves at low temperatures, that could pave the way to a deeper understanding of the mechanisms driving the magnetostructural phase transition in these alloys.

Magnetic-Electrical Synergetic Control of Non-Volatile States in Bilayer Graphene-CrOCl Heterostructures.

Anti-ferromagnetic insulator chromium oxychloride (CrOCl) has shown peculiar charge transfer and correlation-enhanced emerging properties when interfaced with other van der Waals conductive channels. However, the influence of its spin states to the channel material remains largely unknown. Here, this issue is addressed by directly measuring the density of states in bilayer graphene (BLG) interfaced with CrOCl via a high-precision capacitance measurement technique and a surprising hysteretic behavior in the charging states of the heterostructure is observed. Such hysteretic behavior depends only on the history of magnetization, but not on the history of electrical gating; it can also be turned off electrically, providing a synergetic control of these non-volatile states. First-principles calculations attribute this observation to magnetic field-controlled charge transfer between BLG and CrOCl during the phase transition of CrOCl from antiferromagnetic (AFM) to ferrimagnetic-like (FiM) states. This magnetic-electrical synergetic control mechanism broadens the scope of proximity effects and opens new possibilities for the design of advanced 2D heterostructures and devices.

Coexisting Ferromagnetic-Antiferromagnetic State and Giant Anomalous Hall Effect in Chemical Vapor Deposition-Grown 2D Cr5Te8.

Two-dimensional (2D) magnets, as an important member of the 2D material family, have emerged as a promising platform for spintronic devices. Herein, we report the chemical vapor deposition (CVD) growth of highly crystalline submillimeter-scale self-intercalated metallic 2D ferromagnetic (FM) trigonal chromium telluride (Cr5Te8) flakes on inert mica substrates. Through magneto-optical and magnetotransport measurements, we unveil the exceptional magnetic properties of these 2D flakes. The trigonal Cr5Te8 flakes exhibit a strong anisotropic FM order with a Curie temperature above 220 K. Notably, an emergent antiferromagnetic (AFM) state is observed in the MOKE signal from ultrathin Cr5Te8 flakes around the Curie temperature. The AFM state has a relatively weak interlayer exchange coupling, allowing a switching between the interlayer AFM and FM states by tuning the temperature. Meanwhile, the trigonal Cr5Te8 flakes exhibit a giant anomalous Hall effect (AHE), with an anomalous Hall conductivity of 710 Ω-1 cm-1 and an anomalous Hall angle of 3.5% at zero magnetic field, surpassing typical itinerant ferromagnets. Further analysis suggests that the AHE in trigonal Cr5Te8 is primarily driven by the skew-scattering mechanism rather than the intrinsic or extrinsic side-jump mechanism. These findings demonstrate the potential of CVD-grown ultrathin Cr5Te8 flakes as a promising 2D magnetic material with exceptional AHE properties for future spintronic applications.

Giant Topological Hall Effect and Colossal Magnetoresistance in Heusler Ferromagnet near Room Temperature.

Colossal magnetoresistance (CMR) is an exotic phenomenon that allows for the efficient magnetic control of electrical resistivity and has attracted significant attention in condensed matter due to its potential for memory and spintronic applications. Heusler alloys are the subject of considerable interest in this context due to the electronic properties that result from the nontrivial band topology. Here, the observation of CMR near room temperature is reported in the shape memory Heusler alloy Ni2Mn1.4In0.6, which is attributed to the combined effects of magnetic field-induced martensite twin variant reorientation (MFIR) and magnetic field-induced structural phase transformation (MFIPT). This compound undergoes a structural phase transition from a cubic (austenite-L21) ferromagnetic (FM) to a monoclinic (martensite) antiferromagnetic (AFM), which leads to an effective increase in the size of the Fermi surface and consequently in CMR. Additionally, it exhibits significant anomalous Hall conductivity in both antiferromagnetic and ferromagnetic phases. Furthermore, it demonstrates a giant topological Hall resistivity (THR) ≈6µΩ.cm in the vicinity of martensite transition due to the enhanced spin chirality resulting from the formation of magnetic domains with Bloch-type domain walls. The findings contribute to the understanding of the magnetotransport of Ni-Mn-In Heusler alloys, which are prospective candidates for room-temperature spintronic applications.

UOTe: Kondo-Interacting Topological Antiferromagnet in a Van der Waals Lattice.

Since the initial discovery of 2D van der Waals (vdW) materials, significant effort has been made to incorporate the three properties of magnetism, band structure topology, and strong electron correlations-to leverage emergent quantum phenomena and expand their potential applications. However, the discovery of a single vdW material that intrinsically hosts all three ingredients has remained an outstanding challenge. Here, the discovery of a Kondo-interacting topological antiferromagnet is reported in the vdW 5f electron system UOTe. It has a high antiferromagnetic (AFM) transition temperature of 150K, with a unique AFM configuration that breaks the combined parity and time reversal (PT) symmetry in an even number of layers while maintaining zero net magnetic moment. This angle-resolved photoemission spectroscopy (ARPES) measurements reveal Dirac bands near the Fermi level, which combined with the theoretical calculations demonstrate UOTe as an AFM Dirac semimetal. Within the AFM order, the presence of the Kondo interaction is observed, as evidenced by the emergence of a 5f flat band near the Fermi level below 100 K and hybridization between the Kondo band and the Dirac band. The density functional theory calculations in its bilayer form predict UOTe as a rare example of a fully-compensated AFM Cherninsulator.

Magnetic Structure of Ba2CaCo2Si6O17 with Zigzag Spin Chains of Co2+ in High Spin‐3/2 State

The magnetic properties and crystal chemistry of the novel Ba2CaCo2Si6O17 compound exhibiting one‐dimensional zigzag chains of Co2+ ions (S = 3/2) are investigated using powder X‐ray diffraction (PXRD), scanning lectron microscopy, energy dispersive‐Xray spectroscopy, and temperature and field‐dependent magnetic measurements. The refinement of PXRD data suggests a Cmcm space group in orthorhombic symmetry for Ba2CaCo2Si6O17 compound, consisting of a CoO4 tetrahedral network including 1‐D zigzag Co2+ chains. Microstructural and elemental analysis substantiate the proper stoichiometry of the synthesized material. Magnetic measurements show paramagnetic characteristics at room temperature, followed by a transition from paramagnetic to antiferromagnetic (AFM) ordering near 17 K, superimposed with weak ferromagnetic ordering (WFM) characteristics. Magnetic hysteresis (M–H) at 5 K depicts a sigmoid curve with unsaturated magnetization even at high fields. The negative Weiss temperature value ≈−98 K substantiates the strong antiferromagnetic exchange interaction with a frustration index of ≈5.76. The effective paramagnetic moment is 3.34μB, close to the spin‐only value 3.87μB of Co2+ (S = 3/2). The competing and short‐range FM‐AFM interaction is observed because of the zigzag Co2+ chain in the compound. The onset of WFM is attributed to the zigzag magnetic chain‐induced lattice and spin distortion in Ba2CaCo2Si6O17 compound.

An Open-Shell Functionalization of Inorganic Benzene.

A borazine derivative functionalized by nitroxide free radicals, N,N',N″-(tris(4-Bromophenyl))-B,B',B″-tris((2,6-dimethyl-4-(N-tert-butyl-N-oxyamino)phenyl) borazine (TriBNit), was synthesized as a milestone of open-shell inorganic benzene. The crystal structure determined from X-ray diffraction on a single crystal ascertains the grafting of three nitroxide radicals. The temperature dependence of the magnetic susceptibility evidences weak intramolecular antiferromagnetic interactions between the radicals with strong intermolecular antiferromagnetic interactions between two nitroxide moieties of two neighboring molecules. EPR spectroscopy at 80 K on a frozen glassy solution evidences the coexistence of S = 1/2 and S = 3/2 ground-spin state species. This is ascribed to the nitroxide radicals having different orientations with respect to the borazine core giving rise either to antiferromagnetic interaction with a low ground-spin state S = 1/2 or to ferromagnetic interaction with a high ground-spin state S = 3/2 as supported by theoretical data. At room temperature, because of nitroxide mobility, the EPR spectrum is averaged to a ground-spin state S = 1/2.

Copper bromide complexes with triethylbenzylammonium (TEBA): the ladder complex (TEBA)2Cu2Br6, the polymorph dimer α-(TEBA)2Cu2Br6, and the monomeric salt (TEBA)2CuBr4

Two new complexes of copper(II) with bromide ligands and triethylbenzylammonium (TEBA) cations are reported, α-(TEBA)2[Cu2Br6] (1), and (TEBA)2[CuBr4] (2). The syntheses, crystal structures, and magnetic properties are described. 1 crystallizes as bibromide bridged dimers which are linked into square layers via short Br…Br contacts. Variable temperature magnetic susceptibility data indicate ferromagnetic interactions within the dimers (J/kB = 107(4) K) with weak interdimer antiferromagnetic interactions (θ = −3.47(6) K). 2 crystallizes as discrete tetrabromidocuprate anions which are well isolated by the bulk of the TEBA cations. Magnetic susceptibility measurements indicate negligible magnetic interactions in the material. The magnetic properties of the known polymorph (TEBA)2[Cu2Br6] (3) were reexamined in light of the properties of 1 and suggest a significantly stronger interaction within the dimer (J/kB ∼ 110(4) K) than originally proposed. These findings are in agreement considering the nearly identical structures of the Cu2Br6 2- dimers in 1 and 3.

Monolayer M2X2O as potential 2D altermagnets and half-metals: a first principles study

Realizing novel two-dimensional (2D) magnetic states would accelerate the development of advanced spintronic devices and the understandings of 2D magnetic physics. In this paper, we have examined the magnetic and electronic properties of 20 dynamically stable and exfoliable M2X2O (M = Ti-Ni; X = S-Te; excluding Co2Te2O). It has been unveiled that [X4O2]-D2hand [M4]-D4hcrystal fields govern the M-3dorbital splittings in M2X2O. The splittings further lead to the antiferromagnetic (AFM) orderings in Ti2S2O/Fe2S2O/Fe2Se2O/M2X2O (M = V, Cr, Mn and Ni; X = S-Se) as well as the ferromagnetic orderings in Ti2Se2O/Ti2Te2O/Fe2Te2O/Co2S2O/Co2Se2O through kinetic and superexchange mechanisms. Notably, all the AFM M2X2O are 2D altermagnets, and Ti2Se2O/Ti2Te2O/Co2S2O/Co2Se2O are 2D half-metals. In particular, the anisotropicd-d/phoppings lead to the tunable altermagnetic splitting in Ti2S2O/Cr2Te2O, while the parity of V-3dyzorbital contributes to the symmetry-protected altermagnetic splitting within V2X2O. These altermagnetic and half-metallic monolayer M2X2O provide promising candidates applied in low-dimensional spintronic devices. In addition, the potential 2D altermagnetic Weyl semimetal of Fe2S2O/Fe2Se2O, nodal-loop half-metal of Ti2Se2O and half-semi metal of Ti2Te2O facilitate to uncover novel low-dimensional topological physics. These theoretical results would expand the platform in particular for 2D altermagnets and nontrivial systems.

Design, Synthesis, Magnetic Properties, and Hydrogen Evolution Reaction of a Butterfly-like Heterometallic Trinuclear [CuII2MnII] Cluster.

A novel heterometallic trinuclear cluster [CuII2MnII(cpdp)(NO3)2(Cl)] (1) has been designed and synthesized by employing a molecular library approach that uses CuCl2·2H2O and Mn(NO3)2·4H2O as inorganic metal salts and H3cpdp as a multifunctional organic scaffold (H3cpdp = N,N'-bis[2-carboxybenzomethyl]-N,N'-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol). This heterometallic cluster has emerged as an unusual ferromagnetic material and promising electrocatalyst for hydrogen evolution reaction (HER) in the domain of inorganic and materials chemistry. Crystal structure analysis establishes the structural arrangement of 1, revealing a butterfly-like topology with an unusual seven-coordinated Mn(II) center. Formation of this cluster is accomplished by a self-assembly process through functionalization of 1 with one μ2:η1:η1-nitrate and two μ2:η2:η1-benzoate groups via the CuII(μ2-NO3)CuII} and {CuII(μ2-O2CC6H5)MnII} linkages, respectively. Variable-temperature SQUID magnetometry revealed the coexistence of ferromagnetic and antiferromagnetic interactions in 1. The observed magnetic behavior in 1 is unexpected because of a large Cu-O-Mn angle with a value of 132.05°, indicating that the correlation between coupling constants and the structural parameters is a multifactor problem. This cluster shows excellent electrocatalytic performance for the HER attaining a current density of 10 mA/cm2 with a Tafel slope of 183 mV dec-1 at a 310 mV overpotential value. Essentially, cluster 1 shows exceptional electrochemical stability at ambient temperature, accompanied by minimal degradation of the current density as examined by chronoamperometric studies. Density functional theory calculations establish the mechanistic insight into the HER process, indicating that the CuII-OCO-MnII site is the active site for formation of molecular hydrogen.

Antiferromagnetic Spin Wave Amplification by Scattering in the Presence of Non-Uniform Dzyaloshinskii-Moriya Interaction.

In this study, we suggest a method to amplify spin waves (SWs) in antiferromagnets (AFMs). By introducing a non-uniform Dzyaloshinskii-Moriya (DM) interaction, the potential barrier forms a resonant cavity. SWs with an opposite chirality undergo scattering and are resonantly amplified at a phase-matching condition. The calculation is performed in the insulating AFMs where the electric-field-induced DM interaction and pseudo-dipole anisotropy broaden the parabolic-like SW band for multiple resonant modes. Using a transfer matrix method, we also show numerically that scattering between SWs contributes significantly to the SW amplification. Since the electric field selectively amplifies the SWs with resonant frequencies, the proposed device works as an SW transistor and rectifier. This finding will contribute to insulating AFM-based magnon devices where Joule heating is, in principle, avoided.

Spin-Orbit Torque Booster in an Antiferromagnet via Facilitating a Global Antiferromagnetic Order: A Route toward an Energy-Efficient Memory.

Spin transport and the associated spin torque effects in antiferromagnets (AFMs) are scientifically interesting but have remained elusive due to the varied observations of spin transport in AFMs. This study revisits the role of a global Néel order in nickel oxide (NiO) facilitated through a spin-orbit torque (SOT) and examines the enhanced SOT efficiency in a heavy metal (W)/AFM (NiO)/ferromagnet (FM, CoFeB) trilayer with varying NiO thicknesses ranging from 1 to 5 nm. At the as-grown state, the Néel order of NiO is randomly oriented due to the polycrystalline nature of the film structure, leading to increased spin absorption and blocking spin transport from the adjacent W layer. When the spin current amplitude exceeds a threshold value, SOT enables reorientation of the Néel order in NiO to an equilibrium state, forming a global Néel order aligned with the applied current. This long-range Néel order reduces spin absorption and enhances spin transport through NiO, hence boosting the SOT efficiency in the adjacent CoFeB layer. X-ray magnetic linear dichroism spectroscopy and rewritable Néel order reorientation experiments in a device with orthogonal geometry confirmed the strong correlation between the global Néel order facilitation and the boosted SOT efficiency, which is enhanced larger than 4-fold for both damping- and field-like torques in the trilayer with 5 nm NiO. This study not only reveals the strong correlation between globally facilitated Néel order and spin transport in NiO but also offers a promising manner to promote AFM-based SOT devices toward energy-efficient computing technology.

Electric‐Field‐ and Stacking‐Tuned Antiferromagnetic FeClF Bilayer: The Coexistence of Bipolar Magnetic Semiconductor and Anomalous Valley Hall Effect

AbstractValley polarization from broken inversion symmetry provides a new degree of freedom for carriers, bipolar magnetic semiconductor (BMS) generates a purely spin‐polarized current under a gate voltage, but few systems possess the coexistence of valley polarization and BMS. Based on the recent experimental FeCl2 flakes, reversible electric‐field effect on the valley‐ and spin‐polarized Janus FeClF bilayer with different stackings are investigated herein. Janus FeClF bilayers in all three stacks possess interlayer antiferromagnetic (AFM) and intralayer ferromagnetic (FM) couplings. The most stable A (Cl‐Fe‐F‐Cl‐Fe‐F) stack possesses concurrent and spontaneous BMS nature and valley polarization with perpendicular magnetic anisotropy (PMA), while B (Cl‐Fe‐F‐F‐Fe‐Cl) and C (F‐Fe‐Cl‐Cl‐Fe‐F) stacks exhibit AFM semiconductor characters without valley polarization. Electric‐field achieves a transition of BMS and AFM semiconductor. Large ferrovalley (≈108 meV) exists and is mainly contributed by Fe‐dxy and orbitals. With the out‐of‐plane to in‐plane to out‐of‐plane transition of the easy axis, anomalous valley Hall effect (AVHE) can be manipulated to presence and disappearance by perpendicular electric‐field, indicating the valley switch effect (VSE). The coexisting BMS feature, PMA, AVHE and VSE make Janus FeClF bilayer a promising candidate for multifunctional valleytronic and spintronic applications, favoring broad explorations for the low‐dimensional Janus family.