An intrinsic room-temperature half-metallic ferromagnet in a metal-free PN2 monolayer

In spintronics, the embodiment of abundance availability, long spin relaxation time, complete spin-polarization and high Curie temperature (T_C) in intrinsic metal-free half-metallic ferromagnets (MFHMFs) are highly desirable and challenging. In this work, employing density functional theory, we first propose a dynamically, thermally, and mechanically stable two-dimensional (2D) intrinsic MFHMF, i.e. a MoS₂-like PN₂ monolayer, which possesses not only completely spin-polarized half-metallicity, but also an above-room-temperature T_C (385 K). The half-metallic gap is calculated to be 1.70 eV, which can effectively prevent the spin-flip transition caused by thermal agitation. The mechanism of magnetism in the PN₂ monolayer is mainly derived from the p electron direct exchange interaction that separates from usual d-state magnetic materials. Moreover, the robustness of the ferromagnetism and half-metallicity is observed against an external strain and carrier (electron or hole) doping. Surprisingly, electron doping can effectively increase the Curie temperature of the PN₂ monolayer. The proposed research work provides an insight that PN₂ can be a promising candidate for realistic room-temperature metal-free spintronic applications.

High-Throughput Computational Screening for Bipolar Magnetic Semiconductors

Searching ferromagnetic semiconductor materials with electrically controllable spin polarization is a long-term challenge for spintronics. Bipolar magnetic semiconductors (BMS), with valence and conduction band edges fully spin polarized in different spin directions, show great promise in this aspect because the carrier spin polarization direction can be easily tuned by voltage gate. Here, we propose a standard high-throughput computational screening scheme for searching BMS materials. The application of this scheme to the Materials Project database gives 11 intrinsic BMS materials (1 experimental and 10 theoretical) from nearly ~40000 structures. Among them, a room-temperature BMS Li₂V₃TeO₈ (mp-771246) is discovered with a Curie temperature of 478 K. Moreover, the BMS feature can be maintained well when cutting the bulk Li₂V₃TeO₈ into (001) nanofilms for realistic applications. This work provides a feasible solution for discovering novel intrinsic BMS materials from various crystal structure databases, paving the way for realizing electric-field controlled spintronics devices.

Ferromagnetic Double Perovskite Semiconductors with Tunable Properties

The authors successfully dope the magnetically silent double perovskite semiconductor Sr₂ GaSbO₆  to induce ferromagnetism and tune its bandgap, with Ga³⁺ partially substituted by the magnetic trivalent cation Mn³⁺ , in a rigid cation ordering with Sb⁵⁺ . The new ferromagnetic semiconducting Sr₂ Ga_{1- x} Mn_x SbO₆  double perovskite, which crystallizes in tetragonal symmetry (space group I4/m) and has tunable ferromagnetic ordering temperature and bandgap, suggests that magnetic ion doping of double perovskites is a productive avenue toward obtaining materials for application in next-generation oxide-based spintronic devices.

Computational design of double transition metal MXenes with intrinsic magnetic properties

Two-dimensional transition metal carbides (MXenes) have great potential to achieve intrinsic magnetism due to their available chemical and structural diversity. In this work, by spin-polarized density functional theory calculations, we designed and comprehensively investigated 50 double transition metal (DTM) MXenes MCr₂CT_x (T = H, O, F, OH, or bare) based on the chemical formula of M₂C (M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Mo, W). We highlight that ferromagnetic half-metallicity, antiferromagnetic semiconduction, as well as antiferromagnetic half-metallicity have been achieved in the DTM MXenes. Herein, ferromagnetic half-metallic ScCr₂C₂, ScCr₂C₂H₂, ScCr₂C₂F₂, and YCr₂C₂H₂ are characterized with wide band gaps and high Curie temperatures. Very interestingly, the ScCr₂C₂-based magnetic tunnel junction presents a tunnel magnetoresistance ratio as high as 176 000%. In addition, the antiferromagnetic semiconducting TiCr₂C₂, ZrCr₂C₂, and ZrCr₂C₂(OH)₂, possessing moderate band gaps and high Néel temperatures, have been predicted. Especially, the Néel temperature of ZrCr₂C₂(OH)₂ can reach 425 K. Moreover, the Dirac cone-like band structure feature is highlighted in antiferromagnetic half-metallic ZrCr₂C₂H₂. Our study provides a new potential strategy for designing MXenes in spintronics.

Prediction of two-dimensional monolayer C2O2Fe with chiral magnetic and ferroelectric orders

Low-dimensional multiferroics are highly desired for applications and contain exotic physics properties. Here we predict a two-dimensional material, C2O2Fe monolayer, through Fe intercalation in the graphene oxide monolayer. The crystal...

Understanding the role of 5d electrons in ferromagnetism and spin-based transport properties of K2W(Cl/Br)6 for spintronics and thermoelectric applications

The DFT calculation showed the half-metallic nature of K2WCl6 and K2WBr6 with their high Tc. Furthermore, the thermoelectric calculation showed that higher ZT values of K2WCl6 and K2WBr6 originated from ultra-low ke and high PF.

Above-room Curie temperature and barrier-layer-dependent tunneling magnetoresistance in 1T-CrO2 monolayer based magnetic tunnel junction

Van der Waals (vdW) heterostructures based on two-dimensional (2D) ferromagnetic materials hold great potential applications in spintronics. Owing to high Curie temperature (TC) of 392 K as well as moderate...

A new iron-phosphate compound (Fe7P11O38) obtained by pyrophosphate stoichiometric glass devitrification

Iron phosphates are a wide group of compounds that possess versatile applications. Their properties are strongly dependent on the role and position of iron in their structure. Iron, because of its chemical character, is able to easily change its redox state and accommodate different chemical surroundings. Thus, iron-phosphate crystallography is relatively complex. In addition, the compounds possess intriguing magnetic and electric properties. In this paper, we present crystal structure properties of a newly developed iron-phosphate compound that was obtained by devitrification from iron-phosphate glass of pyrophosphate stoichiometry. Based on X-ray diffraction (XRD) studies, the new compound (Fe₇P₁₁O₃₈) was shown to adopt the hexagonal space group P6₃ (No. 173) in which iron is present as Fe³⁺ in two inequivalent octahedral and one tetrahedral positions. The results were confirmed by Raman and Mössbauer spectroscopies, and appropriate band positions, as well as hyperfine interaction parameters, are assigned and discussed. The magnetic and electric properties of the compound were predicted by ab initio simulations. It was observed that iron magnetic moments are coupled antiferromagnetically and that the total magnetic moment of the unit cell has an integer value of 2 µ_B. Electronic band structure calculations showed that the material has half-metallic properties.

Thickness Dependent Magnetic Transition in Few Layer 1T Phase CrTe2

Room temperature two-dimensional (2D) ferromagnetism is highly desired in practical spintronics applications. Recently, 1T phase CrTe₂ (1T-CrTe₂) nanosheets with 5 and thicker layers have been successfully synthesized, which all exhibit the properties of ferromagnetic (FM) metals with Curie temperatures around 305 K. However, whether the ferromagnetism therein can be maintained when continuously reducing the nanosheet's thickness to monolayer limit remains unknown. Here, through first-principles calculations, we explore the evolution of magnetic properties of 1 to 6 layer CrTe₂ nanosheets and several interesting points are found: First, unexpectedly, monolayer CrTe₂ prefers a zigzag antiferromagnetic (AFM) state with its energy much lower than that of FM state. Second, in 2 to 4 layer CrTe₂, both the intralayer and interlayer magnetic coupling are AFM. Last, when the number of layers is equal to or greater than 5, the intralayer and interlayer magnetic coupling become FM. Such highly thickness dependent magnetism provides a new perspective to control the magnetic properties of 2D materials.

Ferromagnetism and intrinsic half-metallicity of two-dimensional MnN monolayer with square-octagonal structure

The MnN monolayer with square-octagonal structure (so-MnN) is explored using density functional calculations. The results show that theso-MnN monolayer is energetically, dynamically, thermally and mechanically stable, and exhibits the ferromagnetism and intrinsic half-metallicity. The total magnetic moment is 16 μ_Bin unit cell (Mn₄N₄). The energy band of spin-up crosses the Fermi energy level (E_F), while the spin-down channel has semiconductor characteristic with a direct band gap of 3.0 eV at Γ-point. By applying the biaxial strain, the band gap in spin-down channel can be tuned, and theso-MnN monolayer still possesses the characteristic of ferromagnetism and intrinsic half-metallicity. Finally, the Curie temperatureT_Cincreases gradually under biaxial strains from 0 to +3%, while theT_Chas a decreasing trend under the biaxial strains from 0 to -3%.

Alkaline earth atom doping-induced changes in the electronic and magnetic properties of graphene: a density functional theory study

Density functional theory was used to investigate the effects of doping alkaline earth metal atoms (beryllium, magnesium, calcium and strontium) on graphene. Electron transfer from the dopant atom to the graphene substrate was observed and was further probed by a combined electron localization function/non-covalent interaction (ELF/NCI) approach. This approach demonstrates that predominantly ionic bonding occurs between the alkaline earth dopants and the substrate, with beryllium doping having a variant characteristic as a consequence of electronegativity equalization attributed to its lower atomic number relative to carbon. The ionic bonding induces spin-polarized electronic structures and lower workfunctions for Mg-, Ca-, and Sr-doped graphene systems as compared to the pristine graphene. However, due to its variant bonding characteristic, Be-doped graphene exhibits non-spin-polarized p-type semiconductor behavior, which is consistent with previous works, and an increase in workfunction relative to pristine graphene. Dirac half-metal-like behavior was predicted for magnesium doped graphene while calcium doped and strontium doped graphene were predicted to have bipolar magnetic semiconductor behavior. These changes in the electronic and magnetic properties of alkaline earth doped graphene may be of importance for spintronic and other electronic device applications.

Alkaline earth atom dopants on graphene induce work function tuning and spin polarized electronic properties by ionic bonding.

Nodal ring spin gapless semiconductor: New member of spintronic materials

INTRODUCTION

Spin gapless semiconductors (SGSs) and nodal ring states (NRSs) have aroused great scientific interest in recent years due to their unique electronic properties and high application potential in the field of spintronics and magnetoelectronics.

OBJECTIVES

Since their advent, all SGSs and NRSs have been predicted in independent materials. In this work, we proposed a novel type of material, nodal ring spin gapless semiconductor (NRSGS), which combines both states of the SGSs and NRSs.

METHODS

The synthesized material Mg2VO4 has been detailed with band structure analysis based on first principle calculations.

RESULTS

Obtained results revealed that there are gapless crossings in the spin-up direction, which are from multiple topological nodal rings located exactly at the Fermi energy level. Mg2VO4 combines the advantages inherited from both NRSs and SGSs in terms of the innumerable gapless points along multiple nodal rings with all linear dispersions and direct contacts. In addition, Mg2VO4 also shows strong robustness against both the spin orbit coupling effect and strain conditions.

CONCLUSION

For the first time, we propose the concept of an NRSGS, and the first such material candidate Mg2VO4 can immediately advance corresponding experimental measurements and even facilitate real applications.

Two-dimensional magnetic materials: structures, properties and external controls

Since the discovery of intrinsic ferromagnetism in atomically thin Cr2Gr2Te6 and CrI3 in 2017, research on two-dimensional (2D) magnetic materials has become a highlighted topic. Based on 2D magnetic materials and their heterostructures, exotic physical phenomena at the atomically thin limit have been discovered, such as the quantum anomalous Hall effect, magneto-electric multiferroics, and magnon valleytronics. Furthermore, magnetism in these ultrathin magnets can be effectively controlled by external perturbations, such as electric field, strain, doping, chemical functionalization, and stacking engineering. These attributes make 2D magnets ideal platforms for fundamental research and promising candidates for various spintronic applications. This review aims at providing an overview of the structures, properties, and external controls of 2D magnets, as well as the challenges and potential opportunities in this field.

Pressure dependent half-metallic ferromagnetism in inverse Heusler alloy Fe2CoAl: a DFT+U calculations

We report the electronic and magnetic properties along with the Curie temperature (T_C) of the inverse full Heusler alloy (HA) Fe₂CoAl obtained by using the first-principles computational method. Our calculations suggests that Fe₂CoAl is a magnetic metal when treated within PBE-GGA under the applied compressive pressures. However, the implementation of electron–electron (U) (i.e., GGA+U) with varying compressive pressure (P) drastically changes the profile of the electronic structure. The application of GGA+U along with pressure induces ferromagnetic half-metallicity with an integer value of total magnetic moment ∼4.0 μ_B per unit cell. The integer value is in accordance with the Slater–Pauling's rule. Here, we demonstrate the variation of semiconducting gap in the spin down channel. The band gap increases from 0.0 eV to 0.72 eV when increasing the pressure from 0 to 30 GPa. Beyond 30 GPa, the electronic band gap decreases, and it is completely diminished at 60 GPa, exhibiting metallic behaviour. The analysis of the computed results shows that the treatment of electron–electron interactions within GGA+U and the application of compressive pressure in Fe₂CoAl enables d–d orbital hybridization giving rise to a half-metal ferromagnet. The T_C calculated from mean field approximation (MFA) decreases up to 30 GPa and then increases linearly up to 60 GPa.

We report the electronic and magnetic properties along with the Curie temperature (T_C) of the inverse full Heusler alloy (HA) Fe₂CoAl obtained using the first-principles computational method.

Proposed mechanical method for switching the spin transport channel in two-dimensional magnetic metal-magnetic semiconductor van der Waals contacts

Developing simple nonmagnetic methods to efficiently control spin transport across magnetic metal-magnetic semiconductor contacts plays a key role in developing high-performance nano-spintronic devices, since a magnetic field is hard to apply locally. For this purpose, based on first principles calculations, we here propose a mechanical means for manipulating the spin transport across two-dimensional magnetic metal-magnetic semiconductor van der Waals contacts formed between representative metallic Fe₃GeTe₂ and semiconducting CrGeTe₃/CrI₃ nanosheets. For such contacts, there exist four spin resolved Schottky barriers, i.e. the n/p-type Schottky barriers in the up/down spin channels, in which the dominant transport spin channel, characterized by the lowest Schottky barrier, can be selectively switched by regulating the magnetic coupling between the magnetic metal and magnetic semiconductor via interfacial sliding. In this way, single spin channel ohmic contacts with reversible spin polarization have been realized.

Magnetism, half-metallicity, and topological signatures in Fe2-xVxPO5 (x = 0, 0.5, 1, 1.5, 2) materials: a potential class of advanced spintronic materials

Novel spintronic materials combining both magnetism and nontrivial topological electronic structures have attracted increasing attention recently. Here, we systematically studied the doping effects, magnetism, half-metallicity, and topological properties in the family of Fe_2-xV_xPO₅ (x = 0, 0.5, 1, 1.5, 2) compounds. Our results show that Fe₂PO₅ takes an antiferromagnetic (AFM) ordering with a zero total magnetic moment. Meanwhile, the material hosts a Dirac nodal line and a Weyl nodal line near the Fermi level. V₂PO₅ is a ferromagnetic (FM) nodal line half-metal with a 100% spin-polarized Weyl nodal line. After doping, we find that Fe_1.5V_0.5PO₅, Fe₁V₁PO₅ and Fe_0.5V_1.5PO₅ all take ferrimagnetic (FiM) ordering, with the Fe and V atoms taking opposite spin directions. Both Fe_1.5V_0.5PO₅ and Fe_0.5V_1.5PO₅ are FiM half-metals. Meanwhile, they show several pairs of fully spin-polarized Weyl points near the Fermi level. Fe₁V₁PO₅ is a FiM semiconductor with different sizes of band gaps in different spin channels. These Fe_2-xV_xPO₅ materials not only provide a good research platform to study the novel properties combining magnetism and nontrivial band topology, but also have promising applications in spintronic applications.

Unraveling the relationship between exposed surfaces and the photocatalytic activity of Ag3PO4: an in-depth theoretical investigation

Over the years, the possibility of using solar radiation in photocatalysis or photodegradation processes has attracted remarkable interest from scientists around the world. In such processes, due to its electronic properties, Ag₃PO₄ is one of the most important semiconductors. This work delves into the photocatalytic activity, stability, and reactivity of Ag₃PO₄ surfaces by comparing plane waves with projector augmented wave and localized Gaussian basis set simulations, at the atomic level. The results indicate that the (110) surface, in agreement with previous experimental reports, displays the most suitable characteristics for photocatalytic activity due to its high reactivity, i.e. the presence of a large amount of undercoordinated Ag cations and a high value work function. Beyond the innovative results, this work shows a good synergy between both kinds of DFT approaches.

Magnetotransport and magnetic properties of amorphous [Formula: see text] thin films

[Formula: see text] is an intermetallic compound with a bulk Curie temperature ([Formula: see text]) of 6-13 K. While existing studies have focused on [Formula: see text] crystals, amorphous thin-films of [Formula: see text] are potentially important since they would be magnetically soft without magnetocrystalline anisotropy, meaning that small external magnetic fields could reverse the direction of their magnetization. Here, we report [Formula: see text] thin-films with a thickness in the 5-200 nm range, deposited by DC magnetron sputtering onto Si(100). Films are amorphous with a weak temperature-dependent resistivity with values ranging between 150 and 300 [Formula: see text] cm. By means of noise spectroscopy, by analyzing the time-dependence of fluctuation-induced voltages, it is found that at low temperatures the resistance fluctuations are due to the Kondo effect. Volume magnetometry indicates [Formula: see text] K with a magnetic coercive field of 30 mT at 5 K for a 125-nm-thick film. The results are promising for the development of Ferromagnet(F)/Superconductor(S)/Ferromagnet(F) pseudo spin-valve devices based on amorphous [Formula: see text] thin films.

Coupling a Crystal Graph Multilayer Descriptor to Active Learning for Rapid Discovery of 2D Ferromagnetic Semiconductors/Half-Metals/Metals

2D ferromagnetic (FM) semiconductors/half-metals/metals are the key materials toward next-generation spintronic devices. However, such materials are still rather rare and the material search space is too large to explore exhaustively. Here, an adaptive framework to accelerate the discovery of 2D intrinsic FM materials is developed, by combining advanced machine-learning (ML) techniques with high-throughput density functional theory calculations. Successfully, about 90 intrinsic FM materials with desirable bandgap and excellent thermodynamic stability are screened out and a database containing 1459 2D magnetic materials is set up. To improve the performance of ML models on small-scale datasets like diverse 2D materials, a crystal graph multilayer descriptor using the elemental property is proposed, with which ML models achieve prediction accuracy over 90% on thermodynamic stability, magnetism, and bandgap. This study not only provides dozens of compelling FM candidates for future spintronics, but also paves a feasible route for ML-based rapid screening of diverse structures and/or complex properties.

Robust intrinsic half-metallic ferromagnetism in stable 2D single-layer MnAsS4

Two-dimensional (2D) intrinsic half-metallic materials are of great interest to explore the exciting physics and applications of nanoscale spintronic devices, but no such materials have been experimentally realized. Using first-principles calculations based on density-functional theory, we predicted that single-layer MnAsS4was a 2D intrinsic ferromagnetic (FM) half-metal. The half-metallic spin gap for single-layer MnAsS4is about 1.46 eV, and it has a large spin splitting of about 0.49 eV in the conduction band. Monte Carlo simulations predicted the Curie temperature (Tc) was about 740 K. Moreover, within the biaxial strain ranging from -5% to 5%, the FM half-metallic properties remain unchanged. Its ground-state with 100% spin-polarization ratio at Fermi level may be a promising candidate material for 2D spintronic applications.

Two-dimensional stable Mn based half metal and antiferromagnets promising for spintronics

In this paper, we predict that the tetragonal MnSi and MnC0.5Si0.5 monolayers are mechanically stable metallic ferromagnetic materials. The thermal stability of the MnC0.5Si0.5 monolayer is verified by our ab initio molecular dynamics (AIMD) result at 300 K. Both MnSi and MnC0.5Si0.5 monolayers exhibit room temperature half-metallic properties, which is very promising for spintronic applications. Both monolayers exhibit large perpendicular magnetic anisotropy, which is desirable for maintaining magnetic order and for high density storage spintronics. A bilayer of the MnSi nanosheet has obviously enhanced thermal stability and exhibits antiferromagnetic metal properties. The Néel temperature could be effectively manipulated and improved by surface functionalization. In addition, monolayer and bilayer MnSi nanosheets exhibit nodal lines in the reciprocal space, and the nodal lines are robust against spin orbit coupling.

Strain robust spin gapless semiconductors/half-metals in transition metal embedded MoSe2monolayer

The realization of spin gapless semiconductor (SGS) and half-metal (HM) behavior in two-dimensional (2D) transition metal (TM) dichalcogenides is highly desirable for their applications in spintronic devices. Here, using density functional theory calculations, we demonstrate that Fe, Co, Ni substitutional impurities can not only induce magnetism in MoSe2monolayer, but also convert the semiconducting MoSe2to SGS/HM system. We also study the effects of mechanical strain on the electronic and magnetic properties of the doped monolayer. We show that for all TM impurities we considered, the system exhibits the robust SGS/HM behavior regardless of biaxial strain values. Moreover, it is found that the magnetic properties of TM-MoSe2can effectively be tuned under biaxial strain by controlling the spin polarization of the 3dorbitals of Fe, Co, Ni atoms. Our findings offer a new route to designing the SGS/HM properties and modulating magnetic characteristics of the TM-MoSe2system and may also facilitate the implementation of SGS/HM behavior and realization of spintronic devices based on other 2D materials.

Electronic Structure and Magnetic Anisotropy of Single-Layer Rare-Earth Oxybromide

The discovery of intrinsic magnetism in two-dimensional (2D) limit has triggered increasing investigations in layered magnetic materials. However, most of the available candidates involves 3d transition metals, while the layered rare-earth magnetic materials are largely unexplored at present. Here, we proposed a series of 2D rare-earth magnetic semiconductors REOBr (RE = Tb, Dy, Ho, Er and Tm) with large magnetic moments and magnetic anisotropy energies using the PBE + U method. Our calculations indicate a half-metallic meta-stable state and a low-energy semi-conducting ground state in these 4f single-layers, which can be characterized by the location of the two-fold degenerate x(x 2 - 3y 2) orbital. The dynamical stability of single-layer REOBr is further confirmed using phonon dispersions. The predicted energy gaps ranging from 2.47 to 4.26 eV decrease with the atomic number of the rare-earth element. Meanwhile, very large spin moments and orbital moments up to 6.018 and 2.872 μB are found, which seem to be insensitive to the magnetic state. Furthermore, the magnetic anisotropy energies are evaluated and understood by a fourth-order non-uniaxial anisotropy mode. Diverse anisotropy energy landscapes including easy cone, easy plane, and easy axis are found, and an extremely high magnetic anisotropy energy of about 8 meV per RE atom is found in the single-layer DyOBr. Our investigations provide a unique insight into layered rare-earth magnetic materials and suggest the single-layer REOBr as competing candidates for low-dimensional data storage applications.

DFT Investigation on the Electronic, Magnetic, Mechanical Properties and Strain Effects of the Quaternary Compound Cu2FeSnS4

The electronic, magnetic and mechanical properties of the quaternary compound Cu2FeSnS4 have been investigated with first principle calculations. Its half-metallicity has been identified with spin polarized band structures and its magnetic origination is caused by the strong spin splitting effect in the d orbitals of Fe atoms. The total magnetic moment of 4 μB is mainly contributed by the Fe atoms and the spatial distribution of the magnetic spin density and charge density difference have also been examined. Moreover, several mechanical properties of Cu2FeSnS4 have been derived and its mechanical stability is also verified. The directional dependent Young’s modulus exhibits relatively small anisotropy yet the shear modulus shows strong directional anisotropy. At last, the tetragonal strain effects have been evaluated and their impact on the electronic and magnetic properties are provided. Results show the total magnetic moment stays almost unchanged while the half-metallicity can only be maintained under relatively small variations for both strains. This study can provide comprehensive information about the various properties of Cu2FeSnS4 compound and serve as a helpful reference for its future applications.

Honeycomb RhI3 Flakes with High Environmental Stability for Optoelectronics

The emerging 2D layered transition metal trihalides (MX₃ ) have attracted extremely high interest given their exceptional structural and physical properties. Continuing to extend the library of 2D MX₃ is essential for exploring new physical phenomena and enabling new functionality. Herein, the optical and electrical properties and the photodetection behavior of atomically thin RhI₃ flakes exfoliated from bulk crystals are reported. This compound exhibits superior air and thermal stability, as well as thickness-dependent bandgap from 1.1 (18L) to 1.4 eV (2L). Field-effect transistors based on the few-layer RhI₃ flakes display n-type semiconducting behavior with competitive mobility of 2.5 cm² V^-1 s^-1 and ON/OFF current ratio of 4 × 10⁴ . Importantly, the outstanding responsivity of 11.5 A W^-1 and high specific detectivity of 2 × 10¹⁰ Jones are recorded from the RhI₃ photodetectors under 980 nm illumination at room temperature in air. These findings indicate a variety of potential applications of atomically thin RhI₃ flakes in future 2D-material-based electronic and optoelectronic devices.

Two-Dimensional Multifunctional Metal-Organic Frameworks with Simultaneous Ferro-/Ferrimagnetism and Vertical Ferroelectricity

Exploring 2D multifunctional materials with intrinsic ferro-/ferrimagnetism and vertical ferroelectricity is a highly desirable but challenging task. Here, motivated by the recently synthesized organometallic frameworks K₃Fe₂[PcFeO₈], we propose to realize such materials in a series of 2D K₃M₂[PcMO₈] (M = Cr-Co) nanosheets. First-principles calculations suggest 2D K₃Cr₂[PcCrO₈] as a ferromagnetic half metal with a Curie temperature of 140 K, whereas others (M = Mn, Fe, and Co) are all ferrimagnetic semiconductors with the Curie temperatures between 66 and 150 K. Moreover, the structural distortion due to the out-of-plane K⁺ counterions leads to a significant vertical electric polarization. The estimated intensity of polarization for K₃Fe₂[PcFeO₈] is 143 pC/m, with the ferroelectric phase-transition barrier being 0.38 eV per formula. This work highlights the potential of 2D organometallic frameworks such as K₃M₂[PcMO₈] as a versatile platform for designing multifunctional materials with simultaneous ferro-/ferrimagnetism and vertical ferroelectricity.

Robust spin manipulation in 2D organometallic Kagome lattices: a first-principles study

The search for 2D ferromagnets with versatile magneto-electronic properties is becoming more active due to their potential applications in spintronic devices. To screen out the optimal compositions, we have explored a series of two-dimensional M3C12X12 (M = 5d transition metals, and X = S, NH, and O) metal-organic frameworks with Kagome lattice patterns through first-principles calculations. By varying the metal center and ligand functional radicals, both the electronic and spin-related properties can be easily tuned to meet the requirements for multifunctional applications in spintronic devices. Among them, Re3C12N12H12 is identified to be a ferromagnetic bipolar magnetic semiconductor with the highest Curie temperature (TC > 330 K). Re3C12O12 is found to be an ideal half-metal with a spin gap of 0.97 eV, which is beneficial for use as a spin-filter. Meanwhile, both Re3C12N12H12 and Re3C12O12 exhibit considerable out-of-plane magnetic anisotropy energies (>26 meV per atom), which benefit the spintronic applications. The theoretical results not only show that the 2D organometallic Kagome lattice is a good platform for designing spintronic materials, but also provides a feasible way to realize robust spin manipulation.

Anisotropic fluoride nanocrystals modulated by facet-specific passivation and their disordered surfaces

Rutile-type fluorides have been proven to be active components in the context of emerging antiferr-omagnetic devices. However, controlled synthesis of low-dimensional, in particular two-dimensional (2D), fluorides in a predictable and deterministic manner remains unrealized because of a lack of efficient anisotropic control, which impedes their further development in reduced dimensions. We report here that altered passivation of {110} growing facets can direct the synthesis of rutile-type fluoride nanocrystals into well-defined zero-dimensional (0D) particulates, one-dimensional (1D) rods and 2D sheets in a colloidal approach. The obtained nanocrystals show positive exchange bias and enhanced magnetic transition temperature from the coexistence of long-range antiferromagnetic order and disordered surface spins, making them strong alternatives for flexible magnetic devices and sensors.

Intrinsic ferromagnetism with high temperature, strong anisotropy and controllable magnetization in the CrX (X = P, As) monolayer

2D ferromagnetic (FM) materials with high temperature, large magnetocrystalline anisotropic energy (MAE), and controllable magnetization are highly desirable for novel nanoscale spintronic applications. Herein by using DFT and Monte Carlo simulations, we demonstrate the possibility of realizing intrinsic ferromagnetism in 2D monolayer CrX (X = P, As), which are stable and can be exfoliated from their bulk phase with a van der Waals layered structure. Following the Goodenough-Kanamori-Anderson (GKA) rule, the long-range ferromagnetism of CrX is caused via a 90° superexchange interaction along Cr-P(As)-Cr bonds. The Curie temperature of CrP is predicted to be 232 K based on a Heisenberg Hamiltonian model, while the Berezinskii-Kosterlitz-Thouless transition temperature of CrAs is as high as 855 K. In contrast to other 2D magnetic materials, the CrP monolayer exhibits a significant uniaxial MAE of 217 μeV per Cr atom originating from spin-orbit coupling. Analysis of MAE reveals that CrP favors easy out-of-plane magnetization, while CrAs prefers easy in-plane magnetization. Remarkably, hole and electron doping can switch the magnetization axis in between the in-plane and out-of-plane direction, allowing for the effective control of spin injection/detection in 2D structures. Our results offer an ideal platform for realizing 2D magnetoelectric devices such as spin-FETs in spintronics.

Black phosphorus as a bipolar pseudospin semiconductor

Semiconductor devices rely on the charge and spin of electrons, but there is another electronic degree of freedom called pseudospin in a two-level quantum system¹ such as a crystal consisting of two sublattices². A potential way to exploit the pseudospin of electrons in pseudospintronics^3-5 is to find quantum matter with tunable and sizeable pseudospin polarization. Here, we propose a bipolar pseudospin semiconductor, where the electron and hole states have opposite net pseudospin polarization. We experimentally identify such states in anisotropic honeycomb crystal-black phosphorus. By sublattice interference of photoelectrons, we find bipolar pseudospin polarization greater than 95% that is stable at room temperature. This pseudospin polarization is identified as a consequence of Dirac cones merged in the highly anisotropic honeycomb system^6,7. The bipolar pseudospin semiconductor, which is a pseudospin analogue of magnetic semiconductors, is not only interesting in itself, but also might be useful for pseudospintronics.

Discovery of stable and intrinsic antiferromagnetic iron oxyhalide monolayers

It is predicted that 2-D FeOX (X = F, Cl, Br, I) are anti-ferromagnetic Mott semiconductors with good structural stabilities, relative high Néel temperature, and large magnetic anisotropy. These materials are promising for building spintronic devices.

Steady semiconducting properties of monolayer PtSe2 with non-metal atom and transition metal atom doping

Based on density functional theory, the electronic structure and magnetic properties of monolayer PtSe₂ doped with different atoms were studied.

Extremely Large Non-equilibrium Tunnel Magnetoresistance Ratio in CoRhMnGe Based Magnetic Tunnel Junction by Interface Modification

Equiatomic quaternary Heusler compounds (EQHCs) generally have the advantages of high Curie temperature, large spin polarization and long spin diffusion length, and they are regarded as one of the most promising candidates for spintronics devices. Herein, we report a theoretical investigation on an EQHC CoRhMnGe based magnetic tunnel junction (MTJ) with (i) MnGe-terminated interface and (ii) modified pure Mn terminated interface, i.e., MnMn-terminated interface. By employing first principle calculations combined with non-equilibrium Green's function, the local density of states (LDOS), transmission coefficient, spin-polarized current, tunnel magnetoresistance (TMR) ratio and spin injection efficiency (SIE) as a function of bias voltage are studied. It reveals that when the MTJ under equilibrium state, TMR ratio of MnGe-terminated structure is as high as 3,438%. When the MTJ is modified to MnMn-terminated interface, TMR ratio at equilibrium is enhanced to 2 × 10⁵%, and spin filtering effects are also strengthened. When bias voltage is applied to the MTJ, the TMR ratio of the MnGe-terminated structure suffers a dramatic loss. While the modified MnMn-terminated structure could preserve a large TMR value of 1 × 10⁵%, even bias voltage rises up to 0.1 V, showing a robust bias endurance. These excellent spin transport properties make the CoRhMnGe a promising candidate material for spintronics devices.

Simultaneous Prediction of the Magnetic and Crystal Structure of Materials Using a Genetic Algorithm

We introduce a number of extensions and enhancements to a genetic algorithm for crystal structure prediction, to make it suitable to study magnetic systems. The coupling between magnetic properties and crystal structure means that it is essential to take a holistic approach, and we present for the first time, a genetic algorithm that performs a simultaneous global optimisation of both magnetic structure and crystal structure. We first illustrate the power of this approach on a novel test system—the magnetic Lennard–Jones potential—which we define. Then we study the complex interface structures found at the junction of a Heusler alloy and a semiconductor substrate as found in a proposed spintronic device and show the impact of the magnetic interface structure on the device performance.

Giant magnetoresistance ratio in a current-perpendicular-to-plane spin valve based on an inverse Heusler alloy Ti2NiAl

A Ti₂NiAl inverse Heusler alloy based current-perpendicular-to-plane (CPP) spin valve (SV) with various kinds of atomic terminated interfaces has been designed to explore the potential application of Heusler alloys in spintronics devices. By performing first principles calculations combined with the nonequilibrium Green's function, it is revealed that spin magnetic moments of interfacial atoms suffer a decrease, and the electronic structure shows that the TiNi^B-terminated structure possesses the largest interface spin polarization of ≈55%. Our study on spin-transport properties indicates that the total transmission coefficient at the Fermi level mainly comes from the contribution from the spin up electrons, which are regarded as the majority of the spin electrons. When the two electrodes of the CPP-SV device are in parallel magnetization configuration, the interface containing Ti and Ni atoms possesses a higher spin up transmission coefficient than the interface containing Ti and Al atoms. The device with the TiNi^B-terminated interface possesses the largest magnetoresistance ratio of 3.28 × 10⁵, and it has great application potential in spintronics devices.

Half-metallic fully compensated ferrimagnetism and multifunctional spin transport properties of Mn3Al

The complete (100%) spin polarization, zero net magnetic moment and high Curie temperature (605 K) make the recently fabricated half-metallic fully compensated ferrimagnet Mn₃Al a promising spintronic material. In order to explore the potential applications in spintronic devices, in this work, we give a theoretical analysis for the Mn₃Al/GaAs(0 0 1) heterostructure and the Mn₃Al/GaAs/Mn₃Al(0 0 1) magnetic tunnel junction. Using the first-principles calculations combined with nonequilibrium Green's function method, we demonstrate from the calculated bias-dependent spin transport properties that the heterostructure exhibits perfect spin filtering effect and spin diode effect, and the magnetic tunnel junction behaves a large tunnel magnetoresistance ratio (up to 10 900%). The physical origins of these versatile spin transport properties are discussed in terms of the half-metallic band structure, the spin-dependent transmission spectra and the band-to-band transmission theory.

High-Temperature Ferromagnetism in an Fe3P Monolayer with a Large Magnetic Anisotropy

For the development of high-performance spintronic nanodevices, one of the most urgent and challenging tasks is the preparation of two-dimensional materials with room-temperature ferromagnetism and a large magnetic anisotropic energy (MAE). Through first-principles swarm-intelligence structural search calculations, we identify an ideal ferromagnetic Fe₃P monolayer, in which Fe atoms show a perfect Kagome lattice, leading to strong in-plane Fe-Fe coupling. The predicted Curie temperature of Fe₃P reaches ∼420 K, and its MAE is comparable to those of ferromagnetic materials, such as Fe and Fe₂Si. Moreover, the Fe₃P monolayer remains as an above room-temperature ferromagnet under biaxial strains as large as 10%. Its lattice can be retained at temperatures of ≤1000 K, exhibiting a high thermodynamic stability. All of these desirable properties make the Fe₃P monolayer a promising candidate for applications in spintronic nanodevices.

Perovskite R{\bar 3}c phase AgCuF3: multiple Dirac cones, 100% spin polarization and its thermodynamic properties

Very recently, experimentally synthesized R{\bar 3}c phase LaCuO₃ was studied by Zhang, Jiao, Kou, Liao & Du [J. Mater. Chem. C (2018), 6, 6132-6137], and they found that this material exhibits multiple Dirac cones in its non-spin-polarized electronic structure. Motivated by this study, the focus here is on a new R{\bar 3}c phase material, AgCuF₃, which has a combination of multiple Dirac cones and 100% spin polarization properties. Compared to the non-spin-polarized system LaCuO₃, the spin-polarized Dirac behavior in AgCuF₃ is intrinsic. The effects of on-site Coulomb interaction, uniform strain and spin-orbit coupling were added to examine the stability of its multiple Dirac cones and half-metallic behavior. Moreover, the thermodynamic properties under different temperatures and pressures were investigated, including the normalized volume, thermal volume expansion coefficient, heat capacity at constant volume and Debye temperature. The thermal stability and the phase stability of this material were also studied via ab initio molecular dynamic simulations and the formation energy of the material, respectively.

Toward Room-Temperature Magnetic Semiconductors in Two-Dimensional Ferrimagnetic Organometallic Lattices

Obtaining room-temperature magnetically ordered two-dimensional (2D) semiconductors is urgently needed for high-speed nanospintronic devices but remains a big challenge. Here, we propose a potential route to solve this issue by constructing ferrimagnetic semiconductors in 2D metal organic frameworks, taking advantage of the high Curie temperature of ferrimagnetic semiconductors and easy tunability of metal organic frameworks. The proposal is confirmed by first-principles design of 2D metal organic frameworks with conjugated electron acceptors diketopyrrolopyrrole (DPP) as organic linkers and transition metal Cr (V) as nodes. The robust ferrimagnetic ordering comes from the strong direct exchange interaction between d-electron magnetic moments on transition metals and charge transfer-induced p-electron magnetic moments on DPPs, which can be modulated facilely by reducing the d-p orbital interaction distance via moderate compressive strain or increasing the d-p orbital charge transfer through introducing electron-withdrawing groups into the DPP moiety.

Electronic Properties of Armchair Black Phosphorene Nanoribbons Edge-Modified by Transition Elements V, Cr, and Mn

The structural, electrical, and magnetic properties of armchair black phosphorene nanoribbons (APNRs) edge-functionalized by transitional metal (TM) elements V, Cr, and Mn were studied by the density functional theory combined with the non-equilibrium Green's function. Spin-polarized edge states introduce great varieties to the electronic structures of TM-APNRs. For APNRs with Mn-stitched edge, their band structures exhibit half-semiconductor electrical properties in the ferromagnetic state. A transverse electric field can then make the Mn-APNRs metallic by shifting the conduction bands of edge states via the Stark effect. The Mn/Cr-APNR heterojunction may be used to fabricate spin p-n diode where strong rectification acts only on one spin.

Spin-dependent carrier mobility and its gate-voltage modifying effects for functionalized single walled black phosphorus tubes

Phosphorene and its derivatives so far have attracted substantial research interest due to its promising properties for developing nanoscale electronic devices. Here, we present a theoretical investigation on the functionalized features, such as the improved electronic structure and carrier mobility, for armchair-edged single walled black phosphorus nanotubes (PNTs) with the substitutional doping of low-concentration transition-metal atoms (Ti, Mn, Fe, and Ni). They are predicted to be exceptional magnetic semiconductors (MSCs), such as half-semiconductor or bipolar MSC. Their spin-resolved carrier mobility at room temperature holds doping element- dependence as well as carrier and spin polarity. Particularly, the difference by two orders of magnitude for carrier mobility emerges due to different TM doping. More interestingly, the carrier mobility in armchair PNTs serving as the channel material of a spin field effect transistor is predicted to be modified strongly by a gate voltage. The enhanced carrier mobility and its gate voltage direction-dependent behavior, as well as the more obvious carrier and spin polarity of mobility, can be observed clearly under gate voltage, which further facilitates the separation of different carriers and spin states and also suggests that realistic carrier mobility is gate voltage-dependent in a field effect transistor.

MnX (X = P, As) monolayers: a new type of two-dimensional intrinsic room temperature ferromagnetic half-metallic material with large magnetic anisotropy

Recent experimentally demonstrated intrinsic two-dimensional (2D) magnetism has sparked intense interest for advanced spintronic applications. However, the rather low Curie temperature and small magnetic anisotropic energy (MAE) greatly limit their application scope. Here, by using density functional theory calculations, we predict a series of stable 2D MnX (X = P, As, Sb) monolayers, among which MnP and MnAs monolayers exhibit intrinsic ferromagnetic (FM) ordering and considerably large MAEs of 166 and 281 μeV per Mn atom, respectively. More interestingly, the 2D MnP and MnAs monolayers exhibit highly desired half-metallicity with wide spin gaps of about 3 eV. Monte Carlo simulations suggest markedly high Curie temperatures of MnP and MnAs monolayers, ∼495 K and 711 K, respectively. Besides, these monolayers are the lowest energy structures in the 2D search space with excellent dynamic and thermal stabilities. A viable experimental synthesis route is also proposed to produce MnX monolayers via the selective chemical etching method. The outstanding attributes of MnP and MnAs monolayers would substantially broaden the applicability of 2D magnetism for a wide range of applications.