Half-metal Research Articles

Terahertz Spectral Signatures of Ultrafast Spin Transports in Ferromagnetic Heusler Alloy

AbstractAlthough the Co‐based Heusler compounds are predicted to be half‐metals, their sub‐picosecond demagnetization dynamics upon laser excitation show a transition‐metal‐like behavior. Any possible role of ultrafast nonlocal spin transport on the ultrafast demagnetization of half‐metallic Heusler compounds has only been inferred indirectly by time‐resolved magneto‐optical Kerr effect. Here, an ultrafast optically driven spin current traveling from Co2FeSi half metal into an adjacent Pt layer by using terahertz (THz) emission time‐domain spectroscopy (TDS) is demonstrated. By varying the magnetic field and excitation symmetry, the sizable THz generation from Co2FeSi/Pt stack arises from optically induced spin transport across the Co2FeSi/Pt interface in conjunction with spin‐to‐charge current conversion, via the inverse spin Hall effect (ISHE). The chemical ordering, interface roughness and magnetization of the samples become vital to engineer the THz emission properties. The amplitude of THz emission is comparable to that of CoFeB/Pt stack, thereby indicating Co2FeSi as an efficient ultrafast light‐driven spin current injector. Finally, by varying the pumping energy, the contributions are distinguished to the ultrafast spin current from thermalization and optical excitation of majority spins in Heusler alloy. This work illustrates THz emission TDS as a powerful tool to investigate the ultrafast spintronic properties of Heusler alloy/normal‐metal bilayers.

Transition metal doping and co-doping effect on electronic and magnetic properties of zb-ScN

The ab-initio study of electronic and magnetic properties and Curie temperature of transition metal (TM) doped ScN diluted magnetic semiconductor (DMS) are calculated using generalized gradient approximation (GGA) implemented in AKAI-KKR-CPA package. The total and partial density of states (DOS) of pure zinc blend ScN as well as TM doped compounds are plotted for different concentrations of dopants. Our results shows that the Sc substituted by TM materials induces a half-metallic character in the system for different concentrations except for Sc1−xNixN (x > 8%). Also, We found that the Sc1−xVxN, Sc1−xCrxN, Sc1−xMnxN compounds are stable in ferromagnetic states, while Sc1−xCoxN and Sc1−xNixN compounds prefer antiferromagnetic phase. In addition, the minority-spin bands depicted a half-metallic ferromagnetic (HMF) gap and half-metallic (HM) gap. To improve this latest result, doping ScN with double impurities (Co, Ni) is also investigated. As a result, our results show a stable antiferromagnetic state in the majority of cases. The mechanism of exchange interaction is also discussed for all doped systems and the high curie temperature are found for most concentrations. The present results suggest TM doped ScN as potential candidate for spintronic devices.

Electronic and magnetic properties of MoTe2 monolayer doped with single and double transition metals: spin density functional theory

The spin density functional computations are exploited to determine the electronic and magnetic properties of MoTe2 monolayer doped with single and double transition metal atoms (V, Cr, Mn, Fe and Co). These properties are sensitive with the types and numbers of the doping transition metals. The semiconductors with narrow band gaps are shown in Cr and Co single-doped MoTe2 monolayer. V and Mn single-doped MoTe2 monolayer are metal. Fe single-doped MoTe2 monolayer reveals the half-metallic behaviours with a 100% spin polarization. V and Co provide the first-two lowest formation energies and are used for the co-doping studies. MoTe2 monolayers simultaneously doped with two Co are characterized as half metal, while the others are metal. The p-d and d-d hybridization around the Fermi level introduce the magnetism, called double exchange mechanism.

Designing a functionalized 2D-TMD (MoX2, X = S, Se) hosting half-metallicity for selective gas-sensing applications: Atomic-scale study

Half metallicity is a desirable property not only for spintronic devices but also for selective gas sensing applications. The scope of the present investigation is to search/design transition-metal “TM” doped transition-metal dichalcogenide “TMD” monolayers (MoX2, X = S, Se) that can host half-metallicity. The screening of various TMs, using spin-polarized DFT calculations, yielded positive results on (Mn, Fe, and Ni)-doped MoS2 MLs and (V, Mn, Fe, and Co)-doped MoSe2 to host half-metallicity when smaller samples of sizes 4 × 4, 5 × 5, and 6 × 6 primitive cells (PCs) are considered. The half-metallicity disappears for larger samples. The origin of this phenomenon can be attributed to the existence of ferromagnetic-coupling (FMC) interactions, governing the ground-state, involving the TM-dopant with its six mirror images, formed by the periodic-boundary conditions. The disappearance of half metallicity is also associated with a drastic change in magnetization (|ΔM|≫ 0). The critical length for the existence of FMC is found to be dependent on both the host crystal and the type of magnetic impurity; at the average is of the order of Lc ∼ 20 Å. Furthermore, we investigated the relevance of half-metallicity to gas-sensing applications (e.g., specifically, MoSe2:Mn ML was taken as an example). In this latter particular case, our results showed the half-metallicity to be a useful property that can be explored for selective gas-sensing of NO2 gas molecules. Our theoretical results are benchmarked to the available data in literature and found to be in good agreement with them.

Modulating spintronic properties of transition metals doped GaN nanotubes with high Curie temperature

AbstractBetween the ferromagnetic semiconductors of the III‐V group, the transition metals (TMs) doped gallium nitride (Ga, TM)N diluted magnetic semiconductor (DMS) shows the most well‐understood and promising applications in spintronic, due to its high Curie temperature. In this research, electronic and magnetic properties of pure armchair (3, 3) and zigzag (5, 0) gallium nitride nanotubes (GaNNTs) and doped with TMs are investigated using the spin‐polarized density functional theory. The spin‐polarized DOS revealed that pure zigzag and armchair GaNNTs are nonmagnetic semiconductors with a direct and indirect bandgap, respectively, in contrast, TMs doped GaNNTs are DMS or half metals (HM). Our results show a high Curie temperature of more than 823 K for Cr and Mn doping, indicating may be good room‐temperature ferromagnetic material for spintronic applications in the future. 11% Cr and Mn atoms doped (3, 3) GaNNT are HM with 100% spin polarization and appear to be good candidates for spintronic applications and especially as spin filter devices.

Transition metals doped (3,3) armchair boron nitride nanosheet as dilute magnetic semiconductors materials for the spintronic application

AbstractMagnetic 2D materials have attracted considerable attention for their significant potential application in spintronic. In this work, the effect of substitutional doping of 3d‐transition metals such as Co, Cr, Mn, and Fe on the magnetic and electronic properties of boron nitride nanosheet (BNNS) was studied based on the spin‐polarized density functional theory. The results revealed that the non‐magnetic and semiconducting behavior of BNNS can be altered by magnetically active dopants. The spin‐polarized density of states suggests that pure BNNS is a nonmagnetic semiconductor with a direct bandgap while transition metals doped BNNS are dilute magnetic semiconductors or half metals (HM). Co doping shows the most stable ferromagnetic phases in the nanosheet. A pair of Mn and Co atoms doped BNNS in edge structure show HM property with 100% spin polarization and seem to be good candidates for spintronic applications and especially as spin filter devices and spin current injectors.

Synergetic effects of combining TM single- and double-atom catalysts embedded in C2N on inducing half-metallicity: DFT study

Designing 2D-materials that exhibit half-metallic properties is crucially important in spintronic devices that are used in low-power high-density logic circuits. The large pores in the C2N morphology can stably accommodate various configurations of transition-metal (TM) atoms that can lead to ferromagnetic (FMC) and anti-ferromagnetic coupling interactions among them, and thus paving the way for achieving half-metallic characteristics. In the present study, we use manganese ‘Mn’ as a promising catalyst and the spin-polarized density-functional theory to search for suitable configurations of metal atoms that yield half-metallicity. Test samples comprised of single-atom catalyst (SAC) and double-atom catalyst (DAC) of Mn embedded in a C2N sample of size 2 × 2 primitive cells as well as their combinations in neighboring large pores (i.e. SAC–SAC, SAC–DAC, and DAC–DAC). Tests were extended to screen many other TM catalysts and the results showed the existence of half metallicity in just five cases: (a) C2N:Mn (DAC, SAC–SAC, and SAC–DAC); (b) C2N:Fe (DAC); and (c) C2N:Ni (SAC–DAC). Our results further showed the origins of half-metallicity to be attributed to FMC interactions between the catalysts with the six mirror images, formed by the periodic-boundary conditions. The FMC interaction is found to have strength of about 20 meV and critical length scale up to about ∼21–29 Å, dependent on both the type of magnetic impurity and the synergetic effects. The potential relevance of half-metallicity to spintronic device application is discussed. Our theoretical results have been benchmarked to the available data in literature and they were found to be in good agreements.

Structure, half-metallic and magnetic properties of bulk and (001) surface of Rb2XMoO6 (X = Cr, Sc) double perovskites: a DFT + U study

Half-metallic (HM) ferromagnets (HM-FMs) with large HM gap and high Curie temperature (TC) have a great importance in the field of spintronics. In this study, the geometric features, electronic structure and magnetism of two new double perovskites (DPs) represented by Rb2XMoO6 (X = Cr, Sc) were explored in bulk phase and (001) surface using quantum mechanical total energy calculations based on density functional theory (DFT). The results showed that optimized lattice constant a is 7.96 Å and 8.26 Å for Rb2CrMoO6 (RCMO) and Rb2ScMoO6 (RSMO), respectively, in the cubic phase (space group Fm-3m, #225). The cohesive energy Ecoh, formation energy Efor and elastic constants (mechanical) calculations proved that present materials are stable. The magnetic properties were explored in terms of ground state magnetic coupling, total magnetic moment (M) and atomic magnetic moment (m), exchange energy (J), and Curie temperature. It was found that both materials have ferromagnetic coupling in the ground state, with M of integer value of 8.0 μ B (4.0 μ B), J value of 47 meV(72 meV) and TC of 365 K (557 K) in Rb2CrMoO6 (Rb2ScMoO6). The electronic properties computed with electronic band structure and density of states demonstrated both DPs to be half-metal with HM gap of 1.61 eV (2.1 eV) in Rb2Cr-based (Rb2Sc-based) system. Finally the electronic and magnetic properties of (001) surfaces were investigated and compared with that of bulk phase. Interestingly, bulk HM property was retained in RSMO, but disappeared in RCMO due the emergence of defect states at Fermi level (EF). The reported results suggest that Rb-based DPs carry some fascinating properties for spin-based devices.

Tuning the magnetic and electronic properties of monolayer SnS2 by 3d transition metal doping: A DFT study

Tin disulfide (SnS 2 ) is a member of the layered metal dichalcogenides family. Monolayer SnS 2 is a semiconductor with an indirect bandgap of 2.43 eV. It is a nonmagnetic semiconductor. In this article, we systematically study the electronic and magnetic properties of 3 d transition metal atom-doped monolayer SnS 2 . The spin-polarized First-principles calculations reveal that Sn-poor condition is the energetically favourable condition to substitute all the 3 d transition metal atoms into SnS 2 monolayer at the Sn-site. We observe that, in all the doped systems, the denser valence bands are filled with the hybridized impurity 3 d and S-3 p orbitals. Here we show that, Sc-doped SnS 2 is a nonmagnetic metal, and Ti and Ni-doped systems are nonmagnetic semiconductors. Single V, Cr, Mn, Fe, Co, Cu, and Zn atom doped systems with a dopant concentration of 6.25% are semiconductors with an induced magnetic moment of 1, 2, 3, 2, 1, 0.688, and 1.275 μ B , respectively. Among them, Cu and Zn-doped systems are direct bandgap semiconductors. With a dopant concentration of 4.08%, the double Fe and Co-doped SnS 2 monolayers are ferromagnetic half metals with 4 and 2 μ B , respectively. The double V, Cr, Mn and Zn-doped SnS 2 are ferromagnetic semiconductors with 2, 4, 6 and 2.56 μ B , respectively. Ferromagnetic coupling between the two identical transition metal atoms is attributed to 90° superexchange. These results emphasize the importance of 3 d transition metal doped monolayer SnS 2 for spin injection, spin polarized current generation and other spintronics device applications.

Tunable Sensing and Transport Properties of Doped Hexagonal Boron Nitride Quantum Dots for Efficient Gas Sensors

The electronic, sensing, and transport properties of doped square hexagonal boron nitride (shBN) quantum dots were investigated using density functional theory calculations. The electronic and magnetic properties were controlled by substitutional doping. For instance, heterodoping with Si and C atoms decreased the energy gap to half its value and converted the insulator shBN quantum dot to a semiconductor. Doping with a single O atom transformed the dot to spin half metal with a tiny spin-up energy gap and a wide spin-down gap. Moreover, doping and vacancies formed low-energy interactive molecular orbitals which were important for boosting sensing properties. The unmodified shBN quantum dot showed moderate physical adsorption of NO2, acetone, CH4, and ethanol. This adsorption was elevated by doping due to interactions between electrons in the low-energy orbitals from the doped-shBN dot and π-bond electrons from the gas. The transport properties also showed a significant change in the current by doping. For instance, the spin-up current was very high compared to the spin-down current in the shBN dots doped with an O atom, confirming the formation of spin half metal. The spin-up/down currents were strongly affected by gas adsorption, which can be used as an indicator of the sensing process.

Structural, elastic, thermodynamic, electronic, magnetic, thermoelectric and optical investigation of chromate spinels TCr2O4 [T = V2+, Mn2+, Fe2+] for optoelectronic applications

Spinel oxides (TM2O4) containing transition metals are gaining vast momentum not only for advanced exploration of fundamental properties but also because of their potential as promising materials for various technological applications, such as microwaves, fuel cells, sensors, information storage, supercapacitors, magnetic fluids, photocatalysis and biomedical devices. In this regard, the structural, elastic, thermodynamic, electronic, magnetic, thermoelectric and optical properties of three related chromate spinels (TCr2O4) with 3d transition metals (T2+ = V, Mn, Fe) have been systematically investigated. The Perdew-Burke-Ernzerh (PBE) functional and the exchange-correlation method (PBE + U) based on the generalized gradient approximation were used to investigate these properties. The elastic parameters confirm that TCr2O4 compounds are mechanically stable and possess stiffness and anisotropic properties. The calculated band structures, DOSs and magnetic moments show that the cubic TCr2O4 (Fd-3m) are half-metallic (HM) ferromagnetic compounds due to strong hybridization between their T-3d, Cr-3d and O-2p states. The thermodynamic properties are explained by calculating the melting temperature (Tm), average sound velocity (vm) and Debye temperature (ƟD). High values of these parameters, Tm, νm and ƟD, indicate the high thermodynamic stability of TCr2O4, which allows them to maintain their ground state structures at high temperatures. The thermoelectric properties as a function of temperature illustrate the stability of the current spinel structures. We have also calculated the optical properties, including real ε1(ω) and imaginary ε2(ω) parts of dielectric function ε(ω), conductivity σ(ω), absorption coefficient α(ω), reflectivity R(ω), refractive index n(ω), extinctive index k(ω) and energy loss function L(ω). TCr2O4 exhibits high dielectric constants; low reflectivity and minimal energy loss in the range VL-UV, making these FM-HM compounds promising materials for many optoelectronics devices.

First-principles study to probe the effect of substitution at X and Z sites on the electronic, magnetic and transport properties of Co2X(V, Nb, Ta)Z(Al, Ga, In, Si, Ge, Sn) Heusler alloys

In the present work, we have used density functional theory based electronic structure calculations to probe the role of isovalent substitution at X@(0.5, 0.5, 0.5) and Z@(0, 0, 0) site of Co2X(= Ta, Nb, V)Z(= Al, Ga, In). Further, we probed the role of electron-rich substitution at Z site on the electronic, magnetic and transport properties of half-metallic(HM) Co2TaZ( = Al,Ga,In) full Heusler alloys(FHA). One of our main aims is to study the effect of electron-rich substitution at Z site on the total and partial moments of X and Z sites. We have used the modified Becke–Johnson(mBJ) exchange–correlation term to calculate the HM band-gap. We observe that, isovalent substitution at X and Z sites provides a way to tune the lattice constant in range of ∼5.75 Å to ∼6.16 Å with sustained HM character. Further, it is noticed that the HM band-gap decreases with isovalent substitution (with low atomic number) at X site with maximum and minimum values of 1.09 eV and 0.5 eV, respectively. Isovalent substitution does not affect the total magnetic moment, however, it affects the atomic magnetic moment values. Further, we observe that 25% of substitution of tetravalent atoms (Si, Ge, Sn) at atomic site Z (having Al, Ga, In) enhances the total magnetic moment with a small decrease in the minority band-gap. However, 75 to 100 % of substitutions destroy the half-metallicity, showing an enhancement in the magnetic moment. Temperature dependent spin Seebeck coefficients corresponding to the 25% and 75% of substitution of tetravalent element at Z site exhibit values close to 150 μV/K and 25–75 μV/K, respectively, for temperatures above 400 K. Interestingly, electron rich substitution at Z cite, changes the orientation of the magnetic moment corresponding to the X (Ta) site element. In order to understand in detail the impact of substitution on the local magnetic moment of Co and X site atoms (V, Nb, Ta), we have performed calculations of respective X-ray magnetic circular dichroism(XMCD) spectra and analyzed the results in terms of unoccupied density of states. XMCD spectra of L2,3 edges of Co atom show only small deviation (in the intensity) with the changes in the X and Z sites. Unlike the case of Co atom, we find that the XMCD spectra of M2,3 edges of Ta atom exhibit substantial changes when tetravalent atoms replace the trivalent atoms at the Z site.

Electronic, Magnetic and Optical Properties of Double Perovskite Compounds: A First Principle Approach

Double perovskite compounds (DPCs) have gained much more attention due to their versatile character in the fields of electronics and spintronics. Using density functional theory (DFT) we investigated the electronic, magnetic and optical properties of DPC La2BB′O6 where B = Cr, Sc and V and B′ = Co, Ni. The electronic band gaps suggest these compounds are half-metallic (HF) semiconductors in the spin-up channel and metallic in the spin-down channel. Magnetic properties suggest these are ferromagnetic in nature, so all DPCs are half-metallic ferromagnetic (HM-FM). Furthermore, the compound La2CrCoO6 shows outstanding electronic and optical properties, so it can be used in optoelectronic/spintronic devices.

Emergence of robust half-metallic spin gap and a sizeable magnetic anisotropy in electron-doped Ca[formula omitted]FeOsO[formula omitted

Half-metallic materials having a large band gap (Eg) along with giant magnetocrystalline anisotropy energy (MAE) have been proposed to be crucial for the development of magnetic tunnel junctions. Herein, electron-doped Ca2FeOsO6 (CFOO) double perovskite oxide is investigated by employing ab-initio calculations with the inclusion of Hubbard U and spin–orbit coupling effects. Electron doping is realized by introducing Co+2/Ni+2 ion with 3d7 (t2g3↑t2g2↓eg2↑eg0↓)/3d8 (t2g3↑t2g3↓eg2↑eg0↓) configuration at Fe+33d5 (t2g3↑t2g0↓eg2↑eg0↓) site. The thermodynamical, mechanical, and dynamical stability of these motifs for determining the synthesis feasibility at ambient conditions is established by calculating the formation energetics, elastic constants, and phonon band structure, respectively. The undoped CFOO system displays a ferrimagnetic Mott-insulating behavior due to a strong antiferromagnetic coupling between Fe and Os ions. On the other hand, electron doping induces half metallicity in CFOO, where extra electrons provided by TM-dopants produce a repulsion in the partially filled Os t2g3↓ spin-minority channel. As a consequence, the Os bands near the Fermi level are shifted to higher energetics; resulting in a conducting nature for the doped motifs. Therefore, Os ion remains in the mixed formal valence states of Os+5 and Os+6/Os+7, which reduces the moments as well. Most remarkably, a large Eg of 1.26/1.65 eV exists in the spin-majority channel of Co/Ni-doped structure, which is highly desired to effectively suppress the spin-flipping and affirm the large mean free path for spins along with a high spin-filtering response. Our results also demonstrated that the half metallicity of the studied TM-doped CFOO is robust and can be preserved under a reasonable magnitude of biaxial strains ([110]). Additionally, a sizeable MAE constant of ∼×107 erg/cm3 indicates that these materials could be potential candidates for the data storage devices.

Experimental study of the structural, magnetic, electrical, and mechanical properties of possible half-metallic Co[formula omitted]V[formula omitted]FeGe Heusler alloys

In this study, we experimentally investigated quaternary Heusler alloys Co2−xVxFeGe with 0≤x≤1 prepared by arc melting and annealing, and showed that they are promising candidates for spintronics applications. Single phase microstructures were observed for V compositions from x=0.25 to x=0.625. Other V concentrations were multi-phased. All single phase samples had a face centered cubic crystal structure with a lattice constant that increased linearly with the V concentration. The low-temperature saturation magnetic moments were shown to obey the Slater–Pauling rule of thumb for half-metals, which is a prerequisite for half metallicity. All alloys had high Curie temperatures, which scaled linearly with the saturation magnetic moment, thereby facilitating applications at room temperature and above. Electrical transport measurements were performed to elucidate the electronic structures of the alloys. The temperature dependence of the electrical resistivity was analyzed and discussed in the framework of the two-current conduction model by considering the existence of an energy gap in the electronic spectrum around the Fermi level of the spin down sub-band. High mechanical hardness values were also observed.

Electronic and transport properties of Heusler alloy based magnetic tunneling junctions: A first principles study

In this work, employing density functional theory based electronic structure calculations, we search for an alternative to MgO as a spacer layer in a magnetic tunneling junction(MTJ), with half-metallic(HM) Co2MnSb as an electrode. First, we demonstrate the possibility of designing an all-Heusler alloy based MTJ with semi-conducting(SC) TiCoSb alloy as the spacer material. We probe the robustness of the HM properties of the Mn–Sb/Co interface and show that the HM property is preserved, even with various disorders and defects. The spin-dependent transport behavior indicates that these properties depend sensitively on the heterojunction interfaces and thickness of the spacer material. Further, we study the transport properties of the heterojunctions of Co2MnSb alloy with the well-studied insulator MgO as well as the less-explored systems like, NaCl and AlN. In these three insulating materials, the smallest complex band decay coefficient is associated with Δ1 symmetry, unlike TiCoSb. This feature enables more desirable symmetry-based spin-filtering properties at the Γ point in the 2D Brillouin zone. We further calculate the resistance area (RA) product for all the heterojunctions, important for the realization of highly sensitive magnetic sensors and it is found that the other spacer layers yield a RA product, several orders less in magnitude compared to that of TiCoSb. Our results indicate that NaCl and AlN may be promising as an alternative to MgO as a spacer material. With the chemical compatibilities resulting into minimal interface buckling and an ultra-low RA product, TiCoSb may also be a promising new material for a MTJ with Co2MnSb as electrode, specifically in relation to overcoming the variability and current-injection challenges.

Cr2Ge2Te6 nanoribbons with perpendicular magnetic anisotropy and half metallicity: a DFT study

Cr2Ge2Te6 is an intrinsic ferromagnetic material with a van der Waals layered structure and it shows promise in spintronics applications. In this work, we investigated the edge effects in Cr2Ge2Te6 nanoribbons and the change in magnetic properties considering spin-orbit effects. Edge formation energies evidenced stability in nanoribbons with TeCr edges. Stability remains in these nanoribbons in presence of Te vacancies at the edge. New bonds appear in the nanoribbons due to edge effects and induce half-metal (HM) behavior. The metallic part is dominated by Te-p, Ge-p, and Cr-d orbitals. Both stable nanoribbons present perpendicular magnetic anisotropy. Our results point Cr2Ge2Te6 nanoribbons as key for the construction of spintronic devices since HM materials with perpendicular magnetic anisotropy produce 100% spin-polarized out-of-plane current.

Localization effects and anomalous hall conductivity in a disordered 3D ferromagnet

We have prepared the ferromagnetic Heusler alloy CoFeV0.5Mn0.5Si in bulk form via arc melting. The longitudinal resistivity exhibits a minimum at 150 K, which is attributable to competition between quantum interference corrections at low temperatures and inelastic scattering at higher temperatures. The magnetoresistance (MR) is positive and nearly linear at low temperatures and becomes negative at temperatures close to room temperature. The positive MR in the quantum correction regime is evidence of the presence of the enhanced electron interaction as a contributor to the longitudinal resistivity. Hall effect measurements indicate a carrier concentration of the order of 1022 cm−3, which is nearly 3 orders of magnitude higher than that found in the “parent” material CoFeMnSi. The higher carrier concentration is consistent with the predicted half metallicity of CoFeV0.5Mn0.5Si. The anomalous Hall conductivity of CoFeV0.5Mn0.5Si is temperature independent for temperatures below the resistivity minimum, which is strong evidence of the absence of quantum interference effects on the anomalous Hall conductivity in a 3D ferromagnet.

Quantum anomalous Hall effect in M2X3 honeycomb Kagome lattice

The quantum anomalous Hall (QAH) effect has recently drawn great attention in spintronics with extraordinary property of chiral edge states without dissipation in absence of magnetic field. In M2X3 honeycomb Kagome lattice, numerous two-dimensional materials are predicted to be QAH insulators including metal oxides/sulfides and metal organic lattice. In this work, we proposed a general model to explain the mechanism of Dirac half metal with absence of spin orbital coupling and the nontrivial topological property with spin orbital coupling, which could be induced by combination of electron counting rule, crystal field effect and orbitals hybridization. Based on the mechanism, we further predict that triphenyl-metal lattice M2(C6H4)3 (M = V, Nb, Ta) are all QAH insulators with high Curie temperature and large nontrivial band gap for triphenyl-Nb and triphenyl-Ta lattice.

Two-dimensional intrinsic ferrovalley Janus 2H-VSeS monolayer with high Curie temperature and robust valley polarization

Inspired by the successful synthesis of two-dimensional (2D) V-based Janus dichloride monolayers with intrinsic ferromagnetism and high Curie temperature (T$_{c}$), the electronic structure, spin-valley splitting and magnetic anisotropy of Janus 2H-VSeS monolayers are investigated in detailed using first-principles calculations. The results show that the Janus 2H-VSeS monolayer exhibits a large valley splitting of 105meV, high T$_{c}$ of 278K and good magnetocrystalline anisotropy (0.31meV) contributed by the in-plane d$_{x^{2}-y^{2}}$/d$_{xy}$ orbitals of V atoms. The biaxial strain ($-$8%<$\varepsilon$<8%) can effectively tune the magnetic moments of V atom, valley splitting $\Delta$E, T$_{c}$ and MAE of Janus 2H-VSeS monolayer. The corresponding $\Delta$E and T$_{c}$ are adjusted from 72meV to 106.8meV and from 180K to 340K, respectively. The electronic phase transition from bipolar magnetic semiconductor (BMS) to half-semiconductor (HSC), spin gapless semiconductor (SGS), and half-metal (HM) is also observed due to the change of V 3d-orbital occupation. Due to the broken space- and time-reversal symmetry, the opposite valley charge carriers carry opposite Berry curvature, which leads to prominent anomalous Hall conductivity at the K and K$^{\prime}$ valleys. The maximum modulation of Berry curvature can reach to 45% and 9.5% by applying the biaxial strain and charge carrier doping, respectively. The stable in-plane magnetocrystalline anisotropy and large spontaneous valley polarization make the ferromagnetic Janus 2H-VSeS monolayer a promising material for achieving the spintronics and valleytronics devices.