First-principles predictions of two-dimensional Ce-based ferromagnetic semiconductors: CeF2 and CeFCl monolayers.

2D honeycomb-Kagome (HK) lattices have attracted extensive attention in recent years due to the peculiar electronic and magnetic properties such as the Dirac band, the half-metallicity, and the high Curie temperature. In this Letter, we theoretically investigate the spin transport properties of a recently proposed 2D Dirac spin gapless semiconductor (also known as a Dirac half-metal with zero energy gap in one spin channel) of the Cr2S3 monolayer with the HK lattice. The excellent spin filtering effect and negative differential resistance effect are found at a bias voltage, and interestingly, a temperature difference can also drive the spin filtering effect. These peculiar transport properties can be understood from the Dirac spin gapless semiconductivity and the spin-dependent transmission spectrum. In addition, we predict that, similar to Cr2S3 and Cr2Se3, 2D Cr2Te3 is also a Dirac spin gapless semiconductor with the above room-temperature Curie temperature and a large magneto-crystalline anisotropic energy (MAE). Under a tensile biaxial strain, the MAE can be greatly increased, and the easy magnetization axis is still along the in-plane. All these results are achieved by the first-principles combined with nonequilibrium Green's function method. The present work will stimulate theoretical and experimental studies on spintronic devices and spin caloritronic devices based on more 2D Dirac HK lattices.

The pursuit of van der Waals (vdW) heterostructures with high Curie temperature and strong perpendicular magnetic anisotropy (PMA) is vital to the advancement of next generation spintronic devices. First-principles calculations are used to study the electronic structures and magnetic characteristics of GaN/VS2 vdW heterostructure under biaxial strain and electrostatic doping. Our findings show that a ferromagnetic ground state with a remarkable Curie temperature (477 K), much above room temperature, exists in GaN/VS2 vdW heterostructure and 100% spin polarization efficiency. Additionally, GaN/VS2 vdW heterostructure still maintains PMA under biaxial strain, which is indispensable for high-density information storage. We further explore the electron, magnetic, and transport properties of VS2/GaN/VS2 vdW sandwich heterostructure, where the magnetoresistivity can reach as high as 40%. Our research indicates that the heterostructure constructed by combining the ferromagnet VS2 and the non-magnetic semiconductor GaN is a promising material for vdW spin valve devices at room temperature.

Two-dimensional ferromagnetic semiconductors of rare-earth monolayer GdX2 (X = Cl, Br, I) with large perpendicular magnetic anisotropy and high Curie temperature

Two-dimensional (2D) ferromagnetic semiconductors with high Curie temperature (TC) and magnetic tunability have garnered significant research interest owing to their immense potential in the realm of spintronic devices. Herein, 2D Ising ferromagnetic semiconductor InMoTe3 monolayer with robust ferromagnetic coupling and TC above room temperature is predicted. Additionally, it has been shown that biaxial strain can notably affect the magnetic interactions and TC of InMoTe3 monolayer. The findings in this study suggest that InMoTe3 monolayer holds promise as a candidate for spintronic device applications, thereby encouraging further theoretical and experimental investigations in this field.

Two-dimensional (2D) intrinsic van der Waals ferromagnetic semiconductor (FMS) crystals with strong perpendicular magnetic anisotropy and high Curie temperature (TC) are highly desirable and hold great promise for applications in ultrahigh-speed spintronic devices. Here, we systematically investigated the effects of a biaxial strain ranging between -8% and +8% and doping with different charge carrier concentrations (≤0.7 electrons/holes per unit cell) on the electronic structure, magnetic properties, and TC of monolayer CrSeBr by combining first-principles calculations and Monte Carlo (MC) simulations. Our results demonstrate that the pristine CrSeBr monolayer possesses an intrinsic FMS character with a band gap as large as 1.03 eV, an in-plane magnetic anisotropy of 0.131 meV per unit cell, and a TC as high as 164 K. At a biaxial strain of only 0.8% and a hole density of 5.31 × 1013 cm-2, the easy magnetization axis direction transitions from in-plane to out-of-plane. More interestingly, the magnetic anisotropy energy and TC of monolayer CrSeBr are further enhanced to 1.882 meV per unit cell and 279 K, respectively, under application of a tensile biaxial strain of 8%, and the monolayer retains its semiconducting properties throughout the entire range of investigated strains. It was also found that upon doping monolayer CrSeBr with holes with a concentration of 0.7 holes per unit cell, the perpendicular magnetic anisotropy and TC are increased to 0.756 meV per cell and 235 K, respectively, and the system tends to become metallic. These findings will help to advance the application of 2D intrinsic ferromagnetic materials in spintronic devices.

Materials with large intrinsic valley splitting and high Curie temperature are a huge advantage for studying valleytronics and practical applications. In this work, using first-principles calculations, a new Janus TaNF monolayer is predicted to exhibit excellent piezoelectric properties and intrinsic valley splitting, resulting from the spontaneous spin polarization, the spatial inversion symmetry breaking and strong spin-orbit coupling (SOC). TaNF is also a potential two-dimensional (2D) magnetic material due to its high Curie temperature and large magnetic anisotropy energy. The effective control of the band gap of TaNF can be achieved by biaxial strain, which can transform TaNF monolayer from semiconductor to semi-metal. The magnitude of valley splitting at the CBM can be effectively tuned by biaxial strain due to the changes of orbital composition at the valleys. The magnetic anisotropy energy (MAE) can be manipulated by changing the energy and occupation (unoccupation) states of d orbital compositions through biaxial strain. In addition, Curie temperature reaches 373 K under only −3% biaxial strain, indicating that Janus TaNF monolayer can be used at high temperatures for spintronic and valleytronic devices.

The effects of V doping on the intrinsic properties of SmFe10Co2 alloys: A theoretical investigation

Two-dimensional (2D) magnetic materials have flourished to date, with ferromagnetic (FM) materials providing a broad platform for exploring the novel quantum anomalous Hall (QAH) effect. However, the extremely low working temperature in most QAH candidates significantly limits the experimental realization. Herein, we designed a series of transition metal chalcogenide VX2 (X = S, Se, Te) monolayers using first-principles calculations and investigated their electronic and topological properties. The results indicate that all these materials are dynamically stable FM 2D materials. Notably, VTe2 is identified as an intrinsic room-temperature QAH insulator with the Chern number of C = 1 and a sizable bandgap of 0.14 eV. This large bandgap arises from the band inversion between the spin-up bands contributed by the px and py orbitals of Te atoms. Additionally, VTe2 exhibits a Curie temperature of 444 K, exceeding the room temperature. VS2 and VSe2 monolayers are FM semiconductors whose electronic properties can be turned by applying external strains. Among them, the VSe2 monolayer becomes a QAH insulator with C = 1 under suitable biaxial compressive strains. This study introduces a category of QAH candidates that show significant promise for implementation in spintronic devices.

In recent years, much attention has been paid to new rare-earth-free magnetic materials to avoid using the expensive and limited availability of rare earths. The Mn-based alloys with high magnetic anisotropy and Curie temperature well above room temperature have been regard as good candidate materials in spintronic devices and rare-earth-free magnets. In which, Mn-Ga binary compounds are such materials that exhibit a combination of various technologically important properties including high spin polarization, high perpendicular anisotropy, and high Curie temperature, multiple structures, temperature-induced phase transitions. An important feature of this kind of materials is that their structural and magnetic properties can be tuned with the changes of elemental compositions and annealing conditions to fit a specific practical application [1]. On the other hand, the Mn 3 Ga compound has the hexagonal structure of Ni 3 Sn (D0 19 ) type similar to Mn 3 Ge and Mn 3 Sn, which are known to have the triangular antiferromagnetic spin structure with a small ferromagnetic moment in the c plane. In 1993, H. Niida reported the phase structure and magnetic properties of pseudobinary system Mn 3+δ Ga 1−x Ge x ingots [2]. It was found that the D0 19 -type structure is stable at 873 K in the whole composition range 0 ≤ x ≤ 1.0 with appropriate values of δ. In previous work, we reported the phase evolution, electric and magnetic properties of the annealed Mn 60+x Ga 40-x (x = 0−15) melt-spun ribbons [3]. In this work, Mn 70 Ga 30−x Sn x (x = 5, 10, 15, 20, 30) melt-spun ribbons were prepared by using melt-spinning and subsequently annealing. The effects of Sn substitution for Ga on phase structure, Curie temperature T C , magnetic properties of these annealed Mn-Ga-Sn ribbons have been investigated.

Two-dimensional (2D) intrinsic ferromagnetic materials with large magnetic anisotropy (MA) and high Curie temperature (TC) are desirable for low-dimensional spintronic applications. In this work, a highly stable Janus NbXY (X, Y = S, Se and Te, X ≠ Y) monolayers with intrinsic ferromagnetism is investigated by using first-principles calculations. The results demonstrate that the MAE values of the NbSSe, NbSTe and NbSeTe MLs are as high as −2.185 meV, −4.013 meV and −4.495 meV per unit cell, respectively, which is higher than the previously reported 2D intrinsic ferromagnetic materials such as FeBrI, NiI2, and VSSe MLs etc. And they are still large enough for practical applications. The Curie temperature (Tc) is estimated to be 160 K for NbSSe monolayer, 260 K for NbSTe monolayer, and 200 K for NbSeTe monolayer based on Monte Carlo simulation. The MAE and Tc could be effectively controlled and enhanced by the biaxial strains. The MAE of NbSSe, NbSTe and NbSeTe MLs can be increased by 8.7%, 24.9% and 14.1%, and reach up to −2.375, −5.015 and −5.131 meV at 5% compressive strain, respectively. Remarkably, at 5% tensile strain, the room temperature Tc of 300 K can be reached for NbSTe monolayer, which is rather promising for its practical application. The large magnetic anisotropy energy and controllable Curie temperature make the NbXY monolayers a promising candidate for applications in spintronic devices at the nanoscale and in high-density data storage.

CrP2Se6 monolayer: Two-dimensional intrinsic ferromagnetic half-metal with large magnetic anisotropy and high Curie temperature

Two-dimensional magnetic materials have been increasingly studied and discussed in the field of spintronics due to their unique electronic properties, high spin polarizability, and a variety of magnetic properties. In this paper, we report a new two-dimensional bilayer hexagonal monolayer material bilayer hexagonal structure (BHS)-CrN2 by first-principles calculations. The BHS-CrN2 nanosheet is an intrinsic ferromagnetic semiconductor material, and the Curie temperature obtained by Monte Carlo simulation is 343 K. The absence of a significant imaginary frequency in the phonon spectrum indicates the dynamic stability of BHS-CrN2. After ab initio molecular dynamics simulation, the supercell of BHS-CrN2 remains a complete structure, indicating its thermal stability. The calculated elastic moduli satisfy the Born–Huang criterion, indicating that the BHS-CrN2 system has good mechanical stability. Interestingly, the compressive strain and O atom doping can transform the electronic structure of BHS-CrN2 from a semiconductor to a half-metal, and the Curie temperature of BHS-CrN2 can be further increased to 1059 K when a 5% tensile strain is applied. Furthermore, the BHS-CrN2 in the ferromagnetic state shows a significant in-plane magnetic anisotropy energy of 0.01 meV per Cr, and the CrP2 and CrAs2 show a large out-of-plane magnetic anisotropy energy of 0.207 and 0.988 meV per Cr, respectively. The results show that the intrinsic ferromagnetic semiconductor BHS-CrN2 has good stability, high Curie temperature, and tunable magnetic properties, which is a promising material for room-temperature spintronic devices.

Prediction of two-dimensional M2As (M = Mn, Fe) with high Curie temperature and large perpendicular magnetic anisotropy

Nonmagnetic nitride-based van der Waals magnetic heterostructures, introducing magnetism by constructing heterostructures with a two-dimensional room-temperature intrinsic ferromagnet and manipulating both the charge and the spin degrees of freedom, are important materials for developing high-performance low-dimensional spintronic devices. To obtain the unique physical properties of novel devices, a fundamental physical understanding of this material system is highly desired. The electronic and magnetic properties of the $\mathrm{Al}\mathrm{N}/{\mathrm{VSe}}_{2}$ van der Waals heterostructure are studied systematically by combining first-principles calculations and Schr\"odinger-Poisson simulations. The $\mathrm{Al}\mathrm{N}/{\mathrm{VSe}}_{2}$ van der Waals heterostructure presents superior physical properties such as a large conduction band offset, ferromagnetic ground state, magnetic anisotropy, and high Curie temperature. Meanwhile, the band alignment and Curie temperature of the $\mathrm{Al}\mathrm{N}/{\mathrm{VSe}}_{2}$ van der Waals heterostructure can be modulated by biaxial strain or an electric field, while the easy magnetization axis remains the in-plane direction. Varying the sheet carrier density changes the energy levels, shifts the average charge position, and tilts the conduction band profile. Our method can also be applied to study the interface properties of other van der Waals heterostructure systems.

In the past few years, two-dimensional (2D) high-temperature ferromagnetic semiconductor (FMS) materials with novelty and excellent properties have attracted much attention due to their potential in spintronics applications. In this work, using first-principles calculations, we predict that the H-MnN2 monolayer with the H-MoS2-type structure is a stable intrinsic FMS with an indirect band gap of 0.79 eV and a high Curie temperature (Tc) of 380 K. The monolayer also has a considerable in-plane magnetic anisotropy energy (IMAE) of 1005.70 μeV/atom, including a magnetic shape anisotropy energy induced by the dipole-dipole interaction (shape-MAE) of 168.37 μeV/atom and a magnetic crystalline anisotropy energy resulting from spin-orbit coupling (SOC-MAE) of 837.33 μeV/atom. Further, based on the second-order perturbation theory, its in-plane SOC-MAE of 837.33 μeV/atom is revealed to mainly derive from the couplings of Mn-dxz,dyz and Mn-dx2-y2,dxy orbitals through Lz in the same spin channel. In addition, the biaxial strain and carrier doping can effectively tune the monolayer's magnetic and electronic properties. Such as, under the hole and few electrons doping, the transition from semiconductor to half-metal can be realized, and its Tc can go up to 520 and 620 K under 5% tensile strain and 0.3 hole doping, respectively. Therefore, our research will provide a new, promising 2D FMS for spintronics devices.