Half-metallic State Research Articles

The effect of carrier concentration on the electronic structure and magnetothermal properties of a two-dimensional VTe2 monolayer with a high Curie temperature.

Two-dimensional (2D) magnetic transition metal dichalcogenides have unique electronic properties, ferromagnetism, and tunable properties in low-dimensional systems. In this paper, the structural, electronic, and magnetic properties of the VTe2 monolayer under different carrier concentrations were investigated using first-principles calculations and Monte Carlo (MC) simulations. It is found that by introducing a suitable number of electrons, the VTe2 monolayer can undergo a transition from a semiconductor to a half-metal state, with 100% spin polarization. The magnetocrystalline anisotropy energy is up to 1855.62 μeV in the z-axis direction, which is conducive to maintaining ferromagnetic order above room temperature. In particular, the easy magnetic axis can undergo an in-plane to out-of-plane transition when doped with a small number of holes. In addition, doping can sensitively enhance or weaken the ferromagnetic exchange coupling strength. The magnetothermal results show that the Curie temperature of the VTe2 monolayer is 547 K in the absence of a size effect, and can be further increased to 574 K when hole doping reaches 1.825 × 1013 cm-2 (0.02 holes per atom). Increasing magnetocrystalline anisotropy and magnetic field can also make the Curie temperature larger. Our results suggest the potential applications of VTe2 in spintronics and provide a deeper understanding of the modulation mechanism.

Magnetic structure and magnetic properties of Fe3BO5 and Mn3BO5 ludwigites

The magnetic ground state of transition metal ludwigites Fe3BO5and Mn3BO5was studied via the combination of representations analysis and the following DFT total energy calculations of possible magnetic configurations. The distinct in the magnetic properties of ludwigites was analyzed through estimation of exchange constants. The pressure evolution of manganese magnetic moments in Mn3BO5reveals the site-dependent behavior of magnetic moments. The manganese magnetic moments in 4-2-4 triads experience the sharp decrease above the pressure of 50 GPa, whereas magnetic moments in 3-1-3 triads have the weak dependence on pressure. The pressure-induced transition from half-metal state to metal state is also being found in Mn3BO5.

Design of spintronic devices based on adjustable half-metallicity induced by electric field in A-type antiferromagnetic bilayer NiI2

Exploring the attainment of half-metallic behavior in two-dimensional (2D) materials through external perturbations is a popular area of current research. In this work, we demonstrate, using first-principles calculations, that bilayer NiI2 (bi-NiI2) is an A-type antiferromagnetic (AFM) semiconductor with an indirect bandgap of 0.86 eV, with the most stable configuration being the AB stacking mode. Upon the application of a vertical electric field, the material transforms from its original semiconducting state into a half-metallic state. Moreover, the spin polarization reverses its orientation whenever the direction of the electric field is altered. This intriguing behavior has inspired us to design a spintronic device based on the A-type AFM bi-NiI2. By employing nonequilibrium Green's function (NEGF) combined with density functional theory (DFT) calculations, we find that the device achieves ON/OFF switching by applying vertical electric fields in parallel or anti-parallel configurations in the two leads. The device displays 100 % spin polarization in the parallel configuration (PC) scenario, driven by bias voltage or temperature differences. Utilizing either the parallel or antiparallel configuration (APC) for ON/OFF switching enables the device to exhibit tunneling magnetoresistance (TMR) of up to 1.45 × 1010 % due to bias voltage and up to 1011 % thermal TMR arising from temperature differences between the leads. These findings highlight the potential of NiI2 and A-type AFM bilayers in the design of spintronic devices.

Unveiling elevated curie temperature and exceptional perpendicular magnetic anisotropy in chlorinated monolayer CrI3

Due to the finite band gap and a ferromagnetic ground state, the CrI3 monolayer is attracting great research interests. However, the low Curie temperature of 46 K is one of the major obstacles for spintronics applications. Here, we have investigated the magnetic properties of chlorinated CrI3 monolayer with varying concentration of Cl. We investigated the dynamical and thermal stability by phonon dispersion and ab-initio molecular dynamic simulation. The band gap was decreasing with increasing Cl concentration and a half-metallic state is obtained at Cl concentration of 4.22 × 1014/cm2. The pristine CrI3 monolayer had perpendicular magnetic anisotropy energy of 0.84 meV/Cr. We find that this perpendicular magnetic anisotropy energy can be even enhanced twice by chlorination. Due to the hybridization of I and Cr atom, we found the spin asymmetric density of states in the iodine atom and this strong enhancement in the magnetic anisotropy originated from asymmetric spin features in iodine atom. We propose that the chlorination can increase the Curie temperature up to 204 K and this is almost four times enhanced value. Based on these finding, we propose that the chlorinated CrI3 system can be a promising material for spintronics applications.

Exploring Half-Metallicity in NiO via TM and NTM Doping: Insights from LDA and LDA-SIC approaches

This study utilizes first-principles calculations to investigate the magnetic properties of NiO doped and co-doped with transition metals (TM) such as vanadium (V), chromium (Cr), and manganese (Mn) at low concentrations. By employing local density approximation (LDA) and self-interaction corrected local density approximation (LDA-SIC), we uncover a pronounced half-metallic behavior in the modified NiO systems. Additionally, the introduction of nitrogen into the doped NiO results in a substantial shift in the density of states (DOS), transforming the material from a non-half-metallic to a distinctly half-metallic ferromagnetic state. These findings offer valuable insights into the potential of doped and co-doped NiO for advancing spintronic applications.

Insulating behaviour in room temperature rhombohedral LiNiO2 cathodes is driven by dynamic correlation

Abstract Inspired by the experimental finding of a paramagnetic insulating state in rhombohedral LiNiO2, a lithium-ion battery cathode of great interest, we calculate the electronic, magnetic, and optical properties of LiNiO2 employing a range of single-particle and many-body methods. Within density-functional theory (DFT) using the generalized-gradient approximation (GGA), meta-GGA, and hybrid functionals, we obtain a ferromagnetic half-metallic ground state for rhombohedral LiNiO2, as has been seen previously. Self-consistent GW calculations including self-interaction corrections beyond DFT for various flavours show an electronic band gap albeit with a small quasiparticle peak at the Fermi energy. Moving beyond this, room temperature state-of-the-art dynamical mean-field theory (DMFT) calculations on rhombohedral LiNiO2 show for the first time a gap of combined Mott and charge-transfer character. The paramagnetic insulating state has a band gap of ~0.6 eV, in excellent agreement with experiments and is in sharp contrast to DFT calculations that require the presence of an extra structural symmetry breaking in the form of Jahn–Teller distortions to open a gap. We observe Ni to be in a +2 state in a d 8L configuration, with a charge-transfer ligand hole in O p, and identify the ligand hole state from the DMFT DOS. We further show that whereas DFT shows the presence of an unphysical metallic Drude peak in the optical absorption spectra, DMFT calculations capture the correct form of the optical absorption spectra, and have an excellent match with the calculated band gap as well. Our results clarify that at room temperature, it is the charge transfer gap with a Mott character that causes rhombohedral LiNiO2’s insulating nature; a structural distortion is not required.

Unraveling the microscopic origin of out of plane magnetic anisotropy in VI3

Intrinsic two-dimensional (2D) ferromagnetic (FM) semiconductors have attracted extensive attentions for their potential applications in next-generation spintronics devices. In recent years, the van der Waals material VI3 has been experimentally found to be an intrinsic FM semiconductor. However, the electronic structure of the VI3 is not fully understood. To reveal why the VI3 is a ferromagnetic semiconductor with strong out-of-plane anisotropy, we systematically studied the electronic structure of the monolayer VI3. Our results confirm that the monolayer VI3 is a Mott insulator, and d2 electrons occupy ag and egπ+ orbitals. The half-metallic state is a metastable state with a total energy 0.7 eV higher than the ferromagnetic Mott insulating state. Furthermore, our study confirmed that the VI3 exhibits the out-of-plane magnetic anisotropy, which originates from d2 electrons occupying low-lying ag and egπ+ orbitals. Since the orbital angular momentum of the egπ+ state is not completely quenched, the VI3 has the out-of-plane anisotropy under interplay between the spin-orbit coupling and crystal field. Our study provides valuable guidance for the design of 2D magnetic materials with pronounced out-of-plane anisotropy.

Quantum anomalous Hall effect and half-metal state of valley in VGe2N4 monolayer

Understanding the physical properties of valley and achieving its half metal state is the key to applying the valley degree of freedom. In this study, by first-principles calculations, the VGe2N4 monolayer is demonstrated as a ferrovalley semiconductor with a valley polarization of 48 meV. Furthermore, two means of compressive strain and regulating the electron correlation effect are explored to achieve the half-metal state of valley in the present VGe2N4 monolayer. Interestingly, topological phase transitions from ferrovalley, half-valley metal to quantum anomalous Hall effect state appear with the increase of strain in the VGe2N4 monolayer. More interestingly, half-metal state of valley induced by electronic correlation or strain can occur in VGe2N4 monolayer, which means 100% spin-polarized valley carriers will be excited. In this case, with the action of an in-plane electric field, the VGe2N4 monolayer will present an anomalous valley Hall effect. Based on these results, the related valleytronics devices are designed. Our work emphasizes the entire process from ferrovalley to topological phase transition, and a method for achieving the half-metal state of valley is proposed. Our finding is of great significance for the development of valleytronics.

Electrostatic doping tunable magnetic transition and half-metallicity in the monolayer CrCTe3

The electrical manipulation of the magnetic transition and spin-polarized states has attracted extensive attention in the field of spintronics. In this work, we perform a detailed study on the electronic and magnetic properties of the carrier-doped monolayer CrCTe3 by using first-principles calculation. It is found that, the magnetic transition from Néel-antiferomagnetic (nAFM) to ferromagnetic (FM) is observed in the case of the electron doping, while for hole doping a magnetic transition sequence of nAFM → zigzag-AFM → FM is observed in the monolayer CrCTe3. Interestingly, the carrier doping induced FM ground state always exhibits half-metallicity with full spin polarization. Moreover, the spin polarity of the half-metallic electronic states is opposite for electron and hole doping, meaning that the spin polarization direction can be tuned by manipulating a gate voltage. The Monte Carlo calculations show that the magnetic transition temperature of the doped FM CrCTe3 is rapidly increased with the increasing doping concentration and is extremely expected to achieve room temperature at a suitable doping concentration. These findings demonstrate that the monolayer AFM system possesses a potential application in spintronic devices with electrically tunable spin polarization.

Crystal structure, magnetic and electrical transport properties of titanium-doped half-Heusler alloys Ni1−xTixMnSb

Ni[Formula: see text]TixMnSb polycrystalline alloys in the range [Formula: see text] were synthesized employing the standard solid-phase synthesis method. The crystal, magnetic, as well as electrical properties of the alloys were investigated using neutron powder diffraction and magneto-resistance measurements. The results reveal that the substitution of Ti for Ni within the temperature range of 2.5–300 K does not induce alterations in the crystal and magnetic structures of NiMnSb. The ordered Ni magnetic moment approaches zero. The study of the electrical transport properties of the Ni[Formula: see text]TixMnSb alloys, where [Formula: see text], has demonstrated a half-metallic state at low temperatures and metallic conductivity for temperatures exceeding 160 K. A semiconductor state manifests at titanium concentrations of x = 0.2 and was observed at temperatures below 21 K. The obtained experimental results are elucidated through first-principles theoretical calculations.

Magnetic quadratic nodal lines in half-metallic anode material TiF3: A first-principles study

It is anticipated that nodal line materials may demonstrate unique physical phenomena. The traditional nodal line materials have a linear energy distribution surrounding them. A recent prediction is that systems may similarly stabilize nodal lines with a quadratic or cubic energy dispersion. This work focuses on a half-metal anode material, TiF3, which has already been predicted to host stable ferromagnetism and half-metallicity under Li insertion. Using first-principles calculation, we predicted for the first time that TiF3, a ferromagnetic material, has completely spin-polarized quadratic nodal lines along the Γ-X path. The half-metallic state and the spin-polarized quadratic nodal lines are robust to uniform strains (from −3 to +3 %). TiF3 can be regarded as a promising platform for deepening our comprehension of magnetic quadratic nodal lines in half-metals.

Design of 2D half-metallic [formula omitted] with robust ferromagnetism and high Curie temperature

Two-dimensional 2D ferromagnetic materials featuring intrinsic half-metallicity (HM) and high critical temperature Tc emerge as promising candidates for innovative low-dimensional spintronic devices. In this study, we employ first-principles calculations to predict a novel 2D half-metallic ferromagnet CoAl2S4 monolayer, a member of the layered AB2X4 family. The material’s energetic, mechanical, and dynamical stability is affirmed through analyses of its cohesive energy, elastic constants, and phonon spectrum, respectively. The ferromagnetic behavior observed in CoAl2S4 can be explained by the superexchange interaction of Co-S-Co bonds, consistent with the Goodenough–Kanamori rules. Notably, CoAl2S4 displays robust ferromagnetism with a Curie temperature reaching up to 435 K. The band structures show a large half-metal gap (2.83eV), ensuring the stability of the half-metallic state. Additionally, the CoAl2S4 monolayer demonstrates a preferential easy magnetization along the out-of-plane direction. Consequently, the rich CoAl2S4 monolayer is expected to boost advancements in spintronics, magnetostrictive materials, and magnetic memory devices.

Two-dimensional ferromagnetic V2Cl3Br3 with tunable topological phases

In recent years, there has been significant research focus on topological states in two-dimensional materials, particularly those exhibiting intrinsic magnetic orderings. In this study, we employ theoretical calculations to uncover the remarkable band topology of monolayer V2Cl3Br3. This two-dimensional compound not only possesses a half-metallic ferromagnetic ground state but also demonstrates exceptional thermodynamic and mechanical stabilities. Notably, we observe clean band crossings with complete spin polarization, which manifest as phase transitions between Weyl semimetal states and quantum anomalous Hall states under different magnetization directions. Both of these topological phases exhibit pronounced edge states. Furthermore, utilizing Monte Carlo simulations with the Heisenberg model, we estimate a high Curie temperature of up to 79.2 K, indicating its potential for spintronic development. Additionally, we analyze the mechanical properties of the material, emphasizing its isotropic mechanical behavior, which offers advantageous features for practical applications. These findings establish the foundation for further exploration of practical applications involving two-dimensional ferromagnetic topological states. Importantly, the identified material candidate can be readily incorporated into experimental preparation, thus accelerating progress in topological quantum applications and the development of half-metallic spintronic devices.

Two-dimensional carbon allotrope with remarkable electron mobility and tunable band gap under uniaxial strain engineering

Exploring two-dimensional (2D) materials with unique structures and excellent photoelectric properties has always been the foundation content of carbon-based material science and condensed matter physics research. In this work, on the basis of density functional theory, the structural, mechanical, electrical and optical properties of the pure sp2 hybrid 2D carbon allotropes Orth-C14 and Orth-C16 were comprehensively predicted, and the regulatory mechanism of the uniaxial strain on the stability, elastic mechanics and electronic properties were analysed. Orth-C16 and Orth-C14 are semiconductors and metals with extremely narrow bandgaps, respectively. Interestingly, their electronic properties could be tuned to indirect band gap semiconductors, metals or half-metallic states with Dirac cones by applying uniaxial strain. In addition, the extremely low effective mass (0.009 m0) and remarkable room temperature electron mobility (69,708 cm2V-1s-1) of approximately 70 times greater than that of black phosphorene (1100 ∼ 1140 cm2V-1s-1), as well as the strong absorption capacity of visible light, all of these advantages indicate that Orth-C16 has crucial development potential in the field of electronic information and optoelectronics.

High spin polarization in quaternary Heusler Fe–Rh–Mn–Al alloys

In this theoretical study, we investigate novel quaternary Heusler Fe–Rh–Mn–Al alloys in the X-type structure with different types of atomic ordering in the unit cell within the spin-polarized density functional calculations. The calculations showed that the 24 possible configurations converge to the 6 nonequivalent solutions. Two types of atomic ordering with the lowest total energy Fe(4c)Rh(4d)Al(4b)Mn(4a) and Mn(4c)Al(4d)Fe(4b)Rh(4a) are half-metallic ferrimagnets in which the spin polarization at the Fermi level is close to 100 %. However, no gap is open in the majority spin projection. The following values of the total magnetic moments for these alloys were obtained: 3.01 and 3.19 μB/f.u., respectively. In the other types of atomic ordering, the half-metallic state is not formed. In FeAlRhMn, the magnetic moment on the manganese ion compensates for the moments on the other ions, and the total moment is close to zero. In the types (MnFeRhAl, AlRhFeMn) of atomic ordering with high energies, the metallic state is also realized, and the magnetic moments on the ions are ordered ferrimagnetically. In this work, we analyzed novel quaternary alloys with different types of atomic ordering motivated by the demand for alloys with a high spin polarization, among which the FeRhAlMn and MnAlFeRh alloys were found. Both with a half-metallic ferrimagnetic state and the lowest total energy among these alloys with the same chemical composition, which indicates the stability of the half-metallic state. The other types of atomic ordering are less energetically favorable, those alloys are ferrimagnetic metals with the low spin polarization. Taking into account the half-metallic state and high spin polarization, the quaternary FeRhAlMn and MnAlFeRh alloys have prospects for use in spintronic devices.

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

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

Ferromagnetic topological states in monolayer vanadium halides toward heterostructure applications

Topological states in two-dimensional materials have garnered significant research attention in recent years, particularly those with intrinsic magnetic orderings, which hold great potential for spintronic applications. Through theoretical calculations, we unveil the superior band topology of monolayer vanadium trihalides, with a specific focus on V2Cl6. These two-dimensional compounds exhibit a half-metallic ferromagnetic ground state, showcasing excellent thermodynamic and mechanical stabilities. Remarkably, clean band crossings with complete spin polarization manifest as phase transitions between Weyl semimetal states and quantum anomalous Hall states under different magnetization directions, and both topological phases yield prominent edge states. Furthermore, Monte Carlo simulations estimate a high Curie temperature of up to 381.3 K, suggesting the potential for spintronic development above room temperature. Taking a step forward, we construct two heterojunctions utilizing selected substrates, MoS2 and h-BN. These substrates not only facilitate a suitable lattice integration but also have a negligible impact on the half-metallicity and band topology. These findings lay the groundwork for exploring practical applications of two-dimensional ferromagnetic topological states. Importantly, the presented material candidates have the potential to accelerate the development of room temperature applications and integrate spintronic devices.

Half-metallic state of two-dimensional InO induced by a gate voltage

Half-metallic state of two-dimensional InO induced by a gate voltage

Perovskite-based two-dimensional ferromagnet Sr<sub>2</sub>RuO<sub>4</sub> monolayer

At present, the research on two-dimensional (2D) ferromagnets is mainly concentrated on van der Waals materials, while the successful preparation of strain-free freestanding 2D perovskite films provides a great opportunity for designing 2D ferromagnets beyond van der Waals materials. Perovskite oxide SrRuO<sub>3</sub>, a typical perovskite itinerant ferromagnet, has broad application prospects in many fields. In this work, the lattice dynamics, ground-state structure, electronic and magnetic properties of its perovskite monolayer with formula Sr<sub>2</sub>RuO<sub>4</sub>, as well as the effect of external electric field, are studied by combining first-principles calculation, symmetry analysis and Monte Carlo simulation. The influence of the Hubbard parameter <i>U</i> is also revealed. The results indicate that the ground-state structure under all <i>U</i> values presents the structural phase (space group <i>P</i>4/<i>mbm</i>) generated by octahedral rotation distortion. Similar to the SrRuO<sub>3</sub> bulk, Sr<sub>2</sub>RuO<sub>4</sub> has a monolayer ground-state phase that exhibits ferromagnetism, which is independent of the <i>U</i> value and thus robust. Density functional theory calculation using Hubbard parameter <i>U</i> predicts the ground-state phase of the monolayer to be a ferromagnetic half metal with an out-of-plane easy-magnetization axis, while excluding that the <i>U</i> parameter predicts the ground-state phase to be a ferromagnetic metallic state. The ferromagnetism mainly originates from the strong ferromagnetic exchange interaction between the nearest neighbor spin pairs. The simulated Curie temperature of the Sr<sub>2</sub>RuO<sub>4</sub> monolayer is 177 K, which is close to the value (150 K) of its bulk phase. The out-of-plane electric field does not change the ground-state structure nor ferromagnetism of the Sr<sub>2</sub>RuO<sub>4</sub> monolayer, but can significantly modulate its electronic property and magnetic property. When an external electric field exceeding 0.3 V/Å is applied, the system undergoes a transition from a ferromagnetic half-metal state to a ferromagnetic metallic state. This work indicates the potential application of Sr<sub>2</sub>RuO<sub>4</sub> monolayer in low-dimensional spintrnic devices, and provides a reference for developing perovskite-based 2D ferromagnets and realizing the control of 2D magnetism by electric field.

Magneto-electric coupling beyond van der Waals interaction in two-dimensional multiferroic heterostructures

Exploring two-dimensional (2D) multiferroic systems with strong magneto-electric coupling properties holds significant application value in nanoscale spintronics devices. However, due to the weak interlayer van der Waals interactions, strong magneto-electric coupling in 2D heterostructures is relatively rare. By using first-principles simulations, we demonstrate that in the NiPS3/Sc2CO2 heterostructure, the ferroelectric polarization switching of the Sc2CO2 layer induces a transition in the magnetic ground state of the NiPS3 layer from the ferromagnetic state to antiferromagnetic ordering, accompanied by a transformation from a semiconductor to a half-metallic state. This magnetic phase transition is caused by a novel magneto-electric coupling mechanism: the polarization switching changes the band alignment between the two materials and then induces a significant interlayer charge transfer, leading to the emergence of Stoner itinerant ferromagnetism. In addition, the polarization switching can also change the magnetic anisotropy from an easy magnetization plane to an easy magnetization axis. These results not only offer a promising multiferroic heterostructure for nonvolatile memory devices and magnetic sensors but also provide a feasible approach for designing multiferroic system with strong magneto-electric coupling.