Potential Applications In Spintronics Research Articles

Artificial Intelligence Guided Studies of van der Waals Magnets

AbstractA materials informatics framework to explore a large number of candidate van der Waals (vdW) materials is developed. In particular, in this study a large space of monolayer transition metal halides is investigated by combining high‐throughput density functional theory calculations and artificial intelligence (AI) to accelerate the discovery of stable materials and the prediction of their magnetic properties. The formation energy is used as a proxy for chemical stability. Semi‐supervised learning is harnessed to mitigate the challenges of sparsely labeled materials data in order to improve the performance of AI models. This approach creates avenues for the rapid discovery of chemically stable vdW magnets by leveraging the ability of AI to recognize patterns in data, to learn mathematical representations of materials from data and to predict materials properties. Using this approach, previously unexplored vdW magnetic materials with potential applications in data storage and spintronics are identified.

Magnetic and transport properties of two-dimensional ferromagnet VSe2 with Se vacancies

As a room-temperature van der Waals intrinsic ferromagnetic semiconductor, monolayer VSe2 was studied extensively for both fundamental research and potential low-dimensional semiconductor spintronic applications. Defects are inevitably encountered and can affect the electronic, magnetic, and transport properties during the experimental synthesis of VSe2 monolayer. However, the study of defects in VSe2 monolayer is still lacking at the atomic level. Here, the electronic, magnetic, and transport properties of VSe2 monolayer with Se vacancies are investigated by first-principles density-functional method. With the direction of easy magnetization axes unchanged, introducing Se vacancies results in the decrease of magnetic anisotropy energy and Curie temperature, which can be further increased by applying in-plane biaxial strain. After Se vacancies are introduced, the conductivity of the system decreases, while the larger doping range is obtained for pure spin-polarized current. The transition from semiconductor to half-metal with 100% spin polarization can be realized by introducing Se bivacancy in VSe2 monolayer, which is highly promising for next-generation spin filter, spin injection and spin transport nanodevices.PACS: 61.72.jd; 73.20.At; 75.50.Pp; 75.70.Ak

Evolution of Compensated Magnetism and Spin-Torque Switching in Ferrimagnetic Fe1−xTbx

Compensated ferrimagnets (FIMs) made of rare-earth transition-metal compounds have stimulated increasing interest for enabling fast spin dynamics. Taking $\mathrm{Fe}$-$\mathrm{Tb}$ compounds as an example, substantial efforts have been made on the study of compensated magnetism and its potential spintronic applications. Current-induced spin-orbit torque (SOT) switching and its evolution with compensated ferrimagnetism in these compounds, however, remain to be systematically explored, which motivates the present study. By combining magnetometry and anomalous Hall effect measurements, a compositional magnetization compensation point (${x}_{c}$ = 0.25) is determined for ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x}$ films of a fixed thickness of 6.5 nm. The antiferromagnetic coupling between $\mathrm{Fe}$ and $\mathrm{Tb}$ sublattices is directly revealed by conducting element-specific x-ray magnetic circular dichroism measurements. The evolution of SOT switching as a function of $\mathrm{Tb}$ concentration (x) in $\mathrm{Pt}/{\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x}/\mathrm{Ta}$ multilayers is subsequently investigated. An enhanced SOT efficiency (approximately 3 times) is obtained at ${x}_{c}$ = 0.25. By conducting an endurance test, reliable SOT switching is revealed for over ${10}^{4}$ cycles. Our work suggests that compensated FIMs of composition ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x}$ could be implemented for realizing efficient and stable spin-orbitronic performances.

First-principles study on the electronic and magnetic properties of BN/CrOBr heterostructures

Two-dimensional van der Waals magnetic heterostructures based on intrinsic ferromagnetic materials have potentially useful for realizing novel spintronic devices. Here, the electronic structure and magnetic property of BN/CrOBr heterostructures are investigated by using first-principles calculations. The calculations show that stacking patterns have no significant effects on the band structure of BN/CrOBr heterostructures, BN/CrOBr heterostructures are semiconductors with indirect band gap. The band gaps of CrOBr monolayer in BN/CrOBr heterostructures are reduced compared with the individual one. The total magnetic moment of CrOBr monolayer is not affected by h-BN monolayer. The h-BN monolayer enhances the in-plane magnetic anisotropy of CrOBr monolayer in BN/CrOBr heterostructures depends on stacking pattern. Furthermore, hole doping can switch the easy magnetization axis of BN/CrOBr heterostructure from in-plane to out-of-plane direction. The theoretical results show that BN/CrOBr heterostructure has potential applications in spintronics for its controllable magnetic anisotropy.

Origin of the Anomalous Electrical Transport Behavior in Fe-Intercalated Weyl Semimetal Td -MoTe2.

Weyl semimetal Td -MoTe2 has recently attracted much attention due to its intriguing electronic properties and potential applications in spintronics. Here, Fe-intercalated Td -Fex MoTe2 single crystals (0 < x< 0.15 ) are grown successfully. The electrical and thermoelectric transport results consistently demonstrate that the phase transition temperature TS is gradually suppressed with increasing x. Theoretical calculation suggests that the increased energy of the Td phase, enhanced transition barrier, and more occupied bands in 1T' phase is responsible for the suppression in TS . In addition, a ρα -lnT behavior induced by Kondo effect is observed with x ≥ 0.08, due to the coupling between conduction carriers and the local magnetic moments of intercalated Fe atoms. For Td -Fe0.15 MoTe2 , a spin-glass transition occurs at ≈10 K. The calculated band structure of Td -Fe0.25 MoTe2 shows that two flat bands exist near the Fermi level, which are mainly contributed by the dyz and orbitals of the Fe atoms. Finally, the electronic phase diagram of Td -Fex MoTe2 is established for the first time. This work provides a new route to control the structural instability and explore exotic electronic states for transition-metaldichalcogenides.

Intrinsic magnetism with high critical temperatures and piezoelectricity in 2D transition metal tetraborides

AbstractDeveloping 2D materials with intrinsic magnetism is an essential issue owing to their wide potential applications in spintronics. Here, a type of transition metal tetraborides, TMB4, (TM = TiCo) monolayers were systematically investigated by employing first principles calculations. Our results showed that the predicted structures hold buckled motif, ultrahigh stability and large magnetic anisotropy energy. It is revealed that CrB4, MnB4, and FeB4 monolayers are robust ferromagnetism, differently, TiB4, VB4, and CoB4 monolayers are stable anti‐ferromagnetism. Based on the Monte Carlo simulation, the critical temperatures of these magnetic systems are around 177–755 K. Most importantly, CoB4 monolayer is confirmed to be an antiferromagnetic semiconductor with out‐of‐plane magnetic easy axis and out‐of‐plane piezoelectricity with large piezoelectric stress coefficients. Our study suggests that the 2D TMB4s hold promising applications for spintronic devices and piezoelectric devices.

Reversal of spin-polarization near the Fermi level of the Rashba semiconductor BiTeCl

Spin–orbit coupling forms the physical basis for quantum materials with non-trivial topology and potential spintronics applications. The Rashba interaction is a textbook model of spin–orbit interactions, with charge carriers undergoing linear, isotropic spin-splitting in momentum space. Recently, non-centrosymmetric semiconductors in the family BiTeX (X = Cl, Br, I) have been identified as exemplary Rashba materials due to the strong splitting of their bulk bands, yet a detailed investigation of their spin textures, and their relationships to local crystal symmetry, is currently lacking. We perform high-efficiency spin-resolved photoemission spectroscopy to directly image the spin texture of surface states of BiTeCl, and we find dramatic deviations from idealized behavior, including a reversal of the spin-polarization near the Fermi level. We show that this behavior can be described by higher-order contributions to the canonical Rashba model with the surface states localized to individual trilayers of the crystal. Due to the prominence of these effects near the Fermi level, they should have a strong impact on the spin-dependent transport of carriers.

DFT+U study on the magnetic properties of 3d transition metal doped β borophene

Two-dimensional materials with strong magnetism have attracted extensive attention for their potential application in spintronics. Recently, thess β 12 borophene with stable structure has been successfully synthesized experimentally. However, the β 12 borophene with non-magnetism limits its application in spintronics. The structural, electronic and magnetic properties of pristine and 3d transition metal (TM)-doped β 12 borophene monolayers are studied by means of first-principles calculations based on the GGA + U approach. Our results indicate that the doping of the Ti-, V-, Cr-, Mn-, Fe-, Co- and Ni atoms can induce magnetism in β 12 borophene and comparatively large magnetism can be obtained in Cr-, Mn-, Fe- and Co-doped systems. The Cr-, Mn- and Co-doped β 12 borophene exhibit antiferromagnetic ground states, while ferromagnetic ground state occurs in the Fe-doped system. Particularly, the spin density distribution of the Cr- and Mn-doped β 12 borophene is highly localized, which have a promise for application in magnetic storage devices. Our work provides a valuable theoretical guidance for the further experimental study and application of borophene materials in spintronics. • The doping of the Ti-, V-, Cr-, Mn-, Fe-, Co- and Ni atoms can induce magnetism in β 12 borophene and comparatively large magnetism can be obtained in Cr-, Mn-, Fe- and Co-doped systems. • The Cr-, Mn- and Co-doped β 12 borophene systems exhibit antiferromagnetic ground states, while ferromagnetic ground state occurs in the Fe-doped system. • The spin density distribution of the Cr- and Mn-doped β 12 borophene is highly localized, which have a promise for application in magnetic storage systems.

Robust half-metallicity and tunable ferromagnetism in two-dimensional VClI2

Recent theoretical and experimental discoveries of two-dimensional (2D) ferromagnetic (FM) materials have sparked intense interest for their potential applications in spintronics. 2D FM materials with high spin polarization are extremely desirable for future low-dimensional spintronics. Half-metallicity plays a key role in the development of such devices. Here, we reported a new 2D nanomagnet VClI2 using the first-principles based density functional theory calculations. VClI2 shows an exciting half-metallic character with a wide half-metallic gap of 0.4 eV. The ground state favors ferromagnetic coupling with a Curie temperature Tc of 21 K. The half-metallicity with a FM ground state is further achieved by the application of an external strain and by the combined effects of the strain and the electric field. A phase transition from a half-metallic → semiconductor → metal was further observed under different stimuli with an antiferromagnetic ground state. At Ez=7.5 V/nm and in the presence of η=5% strain, the calculated Tc is estimated at 35 K, which shows a 67% increment than the Tc observed in the unstrained condition. The fascinating and unique properties suggest that VClI2 is a promising two-dimensional ferromagnetic half-metal, which can be useful for applications in future memory devices to enrich the 2D magnetic materials library.

Magnetic Electrides: High-Throughput Material Screening, Intriguing Properties, and Applications.

Electrides are a unique class of electron-rich materials where excess electrons are localized in interstitial lattice sites as anions, leading to a range of unique properties and applications. While hundreds of electrides have been discovered in recent years, magnetic electrides have received limited attention, with few investigations into their fundamental physics and practical applications. In this work, 51 magnetic electrides (12 antiferromagnetic, 13 ferromagnetic, and 26 interstitial-magnetic) were identified using high-throughput computational screening methods and the latest Materials Project database. Based on their compositions, these magnetic electrides can be classified as magnetic semiconductors, metals, or half-metals, each with unique topological states and excellent catalytic performance for N2 fixation due to their low work functions and excess electrons. The novel properties of magnetic electrides suggest potential applications in spintronics, topological electronics, electron emission, and as high-performance catalysts. This work marks the beginning of a new era in the identification, investigation, and practical applications of magnetic electrides.

Stable Room Temperature Nitrenes Created by Photolysis of Crystalline 4-Azido-2,3,5,6-tetrafluorobenzoic Acid

The structure, spectroscopy, and photochemistry of 4-azidobenzoic acid (4ABC) and its perfluorinated analog 4-azido-2,3,5,6-tetrafluorobenzoic acid (4F4ABC) are characterized in frozen glasses and crystals. Photolysis of the parent azides leads to the production of nitrenes and other spin species that are probed by electron paramagnetic resonance and optical spectroscopy. Shifts in the absorption spectra for both the parent azides and the nitrenes were well reproduced using density functional calculations. Photolysis generates ∼10× higher yield of the triplet nitrene relative to the quintet and radical side-products in 4F4ABC, while the opposite ratio is observed in 4ABC. An annealing step further suppressed the side-products in 4F4ABC, creating a solid where nitrenes were the dominant spin species. The nitrene in the 4F4ABC crystal has a 1/e lifetime of 20 days at room temperature in open air. This stability makes it possible to photopattern nitrene centers into a single crystal and characterize their photoluminescence. Multiple observations suggest that the remarkable stability in the 4F4ABC crystal is a consequence of crystal packing that traps N2 molecules adjacent to the nitrene. The ability to create stable, solid-state nitrene samples may provide a route to organic high-spin materials with potential applications in spintronics and quantum information science.

Light-Induced Mott-Insulator-to-Metal Phase Transition in Ultrathin Intermediate-Spin Ferromagnetic Perovskite Ruthenates.

Light control of emergent quantum phenomena is a widely used external stimulus for quantum materials. Generally, perovskite strontium ruthenate SrRuO3 has an itinerant ferromagnetism with a low-spin state. However, the phase of intermediate-spin (IS) ferromagnetic metallic state has never been seen. Here, by means of UV-light irradiation, a photocarrier-doping-induced Mott-insulator-to-metal phase transition is shown in a few atomic layers of perovskite IS ferromagnetic SrRuO3- δ . This new metastable IS metallic phase can be reversibly regulated due to the convenient photocharge transfer from SrTiO3 substrates to SrRuO3- δ ultrathin films. These dynamical mean-field theory calculations further verify such photoinduced electronic phase transformation, owing to oxygen vacancies and orbital reconstruction. The optical manipulation of charge-transfer finesse is an alternative pathway toward discovering novel metastable phases in strongly correlated systems and facilitates potential light-controlled device applications in optoelectronics and spintronics.

Interfacial interaction between graphene and ferromagnets: First principles study

The interfacial interaction between graphene and ferromagnetic substrate is known to bring additional controls to the intrinsic properties of graphene, in addition to inducing some novel properties to the system which may have potential application in spintronics. In this work the spin-polarized electronic structures across the graphene–ferromagnet interface has been investigated using first principles density functional theory calculation as it is implemented on Vienna ab-initio simulation package (VASP). The electronic and magnetic properties of the interface have also been investigated. The ferromagnet substrate was represented by Ni(111) and Co(111) surfaces due to their structural resemblance to graphene. The study reveals that the ferromagnet layers adjacent to the interface show a transition of spin orientation from in plane to out of plane. The critical thickness of the slab which yields the maximum shifting of the spin orientation of the ferromagnet layers is also determined. The strong hybridization between different orbitals of graphene and ferromagnet significantly affects the electronic and magnetic properties of the interface. Reduction on the local magnetic moments of the ferromagnet layers adjacent to the interface and the induced spin polarization on the graphene layer were also observed which is due to the impacts of the hybridization. This work will provide important information which can be used for efficient design of interfaces for graphene-based spintronics.

Ferromagnetism Induced by Magnetic Dilution in Van der Waals Material Metal Thiophosphates

AbstractMetal thio(seleno) phosphates MPX3 attract considerable attention with potential application in spintronics and other types of devices. Here, ferromagnetism in an Ising type diluted magnetic semiconductor Fe1‐xZnxPS3 is reported. Bulk single crystals of Fe1‐xZnxPS3 have been synthesized via chemical vapor transport method and characterized by X‐ray diffraction. The weak ferromagnetism associated with spin/cluster spin glass emerges at 30% Zn doping. A nearly static ferromagnetic order is observed in the highly diluted magnets Fe0.1Zn0.9PS3. X‐ray photoemission measurements indicate introduction of holes and associated Fe3+ in samples with ferromagnetic order. Density functional theory calculations confirm the Ising‐type ferromagnetic state in highly diluted compounds with hole doping. The interplay between bound magnetic polarons induces impurity‐band‐exchange and superexchange interactions can explain the evolution of magnetism with Zn doping. The findings suggest that the magnetic diluted FePS3 system is a candidate for potential applications in magnetic devices, and its quantum mechanism should be explored by using microscopic techniques in the near future.

Spin-Gapless Semiconductors and Quantum Anomalous Hall Effects of Tetraazanaphthotetraphene-Based Two-Dimensional Transition-Metal Organic Frameworks on Spintronics and Electrocatalysts for CO2 Reduction

The two-dimensional metal–organic framework (2D MOF) has potential applications in spintronics and catalytics due to the tunable structure, high crystallinity, and porosity. However, the study of the physical properties of a precise single-crystal 2D MOF is rare because of the small crystals or poor quality, which hinders the practical application. In this work, based on the successful fabrication of 200 μm single-crystal 2D Cu3(HHTT)2 and Ni3(HHTT)2 (HHTT = 2,3,7,8,12,13-hexahydroxy tetraazanaphthotetraphene), the electronic, magnetic, and catalytic properties of 2D M3(HHTT)2 (M = 3d transition metals) were studied by first-principles calculations. Cr3(HHTT)2 and Cu3(HHTT)2 exhibit out-of-plane ferromagnetic spin-gapless semiconductor properties with opposite spin polarization. When the spin-orbit coupling is considered, Cr3(HHTT)2 opens a gap of 3.37 meV around the Fermi level and shows a quantum anomalous Hall effect with the Chern number C = 1. Cr3(HHTT)2 shows a lower overpotential (0.66 eV) than that of Cu3(HHTT)2 (1.94 eV) for electrocatalytic CO2 reduction reactions. Additionally, Mn3(HHTT)2 exhibits robust out-of-plane ferrimagnetic semiconducting properties. M3(HHTT)2 (M = Ti, Fe, and Co) and V3(HHTT)2 exhibit in-plane spin-gapless semiconductor properties with an opposite spin polarization. These results provide candidates for the study of spintronics and electrocatalysts.

First-principal investigations of the electronic, magnetic, and thermoelectric properties of CrTiRhAl quaternary Heusler alloy

Density functional theory (DFT) calculations were performed to investigate the electronic, magnetic, and thermoelectric properties of CrTiRhAl quaternary Heusler alloy (QHA). The type-I atomic configuration was found to be the most stable structure of this alloy. The CrTiRhAl QHA was also found to exhibit a semiconducting behavior with an indirect narrow gap of 0.129 eV at the majority spin channel. On the other hand, the minority spin channel exhibits a metallic behavior. The QHA has a total magnetic moment of 2 μB and 100 % spin-polarization that making it ideal for potential spintronic applications. The Seebeck coefficient, electrical conductivity, and electronic thermal conductivity of CrTiRhAl alloy were calculated using the semi-classical Boltzmann theory. Additionally, the lattice thermal conductivity was predicted using Slack’s equation. The calculations predicted a low figure of merit (ZT) below the Curie temperature, namely 0.4 at 300 K, which can be enhanced by lowering the structural dimensionality or doping for possible thermoelectric applications. However, the ZT value dropped drastically beyond Curie temperature (0.02 at 800 K).

Enhancement of Perpendicular Magnetic Anisotropy and Curie Temperature in V-Doped Two-Dimensional CrSI Janus Semiconductor Monolayer

Two-dimensional (2D) intrinsic ferromagnetic semiconductors (FMSs) with high Curie temperatures (TC) and large perpendicular magnetic anisotropy (PMA) have immense potential in spintronic applications. Recently, the TC of the discovered 2D intrinsic FMSs is below room temperature, and the easy magnetization axis (EMA) is oriented in the in-plane direction. Here, using the first-principle calculations and the Monte Carlo simulations, we investigate the effect of V doping on structure, electronic structure, and magnetic properties of the CrVS2I2 monolayer. The calculated formation energy, phonon dispersion, ab initio molecular dynamics simulations, and elastic constants of the CrVS2I2 monolayer indicate that it is stable at room temperature. More importantly, V doping converts the EMA direction of the CrVS2I2 monolayer from in-plane to out-of-plane, accompanied by a significant enhancement of magnetic anisotropy energy from 0.0011 to 0.997 meV/atom, and it also enhances TC from 175 to 352 K. Moreover, the CrVS2I2 monolayer remains as a semiconductor with a direct band gap of 0.38 eV. Our findings provide a feasible route for the realization of high TC and large PMA in 2D intrinsic FMSs.

Multi-experimental determination of magnetic transition in Weyl semimetals RAlGe

The single crystals of Weyl semimetals or candicate RAlGe (R = La, Ce, Pr and Nd) have been synthesized by self-flux method and confirmed forming in noncentrosymmetric LaPtSi type. Compared with nonmagnetic LaAlGe, the configurations of localized 4f electrons strongly dominate the magnetic, thermal and electric behaviors of other RAlGe. The main critical temperatures for magnetic transition are robust around 5.1 K, 15.4 K and 5.2 K for CeAlGe, PrAlGe and NdAlGe. PrAlGe and NdAlGe have c easy axis with similar anisotropy, but the easy direction for CeAlGe lies in a axis below 12 K. Their λ-shaped specific heat reveal 2nd order phase transitions. The magnetic entropy for PrAlGe and NdAlGe approach to the values of Hund’s ground states at about 60 K and 50 K, while that for CeAlGe reaches 87 % of Rln2 at Tc stemming from a doublet ground state. It’s significant to combine multi-experiments and effective fittings to comparatively explore Weyl RAlGe family for the potential application in spintronics.

Dirac semimetallic Janus Ni-trihalide monolayer with strain-tunable magnetic anisotropy and electronic properties.

Two-dimensional (2D) ferromagnetic (FM) semiconductors have been paid much attention due to the potential applications in spintronics. Here, the electronic and magnetic properties of 2D Janus Ni-trihalide monolayer Ni2X3Y3 (X, Y = I, Br, Cl; X ≠ Y) are investigated by first-principle calculations. The properties of Ni2X3Y3 (X, Y = I, Br, Cl; X ≠ Y) monolayers are compared by selecting the NiCl3 monolayer as the reference material. Ni2X3Y3 monolayers have two distinct magnetic ground states of ferromagnetic (FM) and antiferromagnetic (AFM). In the Ni2X3Y3 monolayer, two different orbital splits were observed, one semiconductor state and the other semimetal state. The semimetal state of Ni2X3Y3 can be tuned to semiconductor or metallic state when biaxial strain is applied. The magnetic anisotropy energy (MAE) of the Ni2X3Y3 monolayer can display variations compared to that of the NiCl3 monolayer, with the direction of easy magnetization being influenced by the specific halogen elements present. The easy magnetization direction of Ni2X3Y3 can also be changed by applying biaxial strain. The Tc of Ni2X3Y3 is predicted to be about 100 K according to the calculation of the EAFM-EFM model. The design of the Janus Ni2X3Y3 structure has expanded the range of 2D magnetic materials, a significant contribution has been made to the advancement of spintronics and its applications.

Recent progress of transport theory in Dirac quantum materials

Dirac quantum materials comprise a broad category of condensed matter systems characterized by low-energy excitations described by the Dirac equation. These excitations, which can manifest as either collective states or band structure effects, have been identified in a wide range of systems, from exotic quantum fluids to crystalline materials. Over the past several decades, they have sparked extensive experimental and theoretical investigations in various materials, such as topological insulators and topological semimetals. The study of Dirac quantum materials has also opened up new possibilities for topological quantum computing, giving rise to a burgeoning field of physics and offering a novel platform for realizing rich topological phases, including various quantum Hall effects and topological superconducting phases. Furthermore, the topologically non-trivial band structures of Dirac quantum materials give rise to plentiful intriguing transport phenomena, including longitudinal negative magnetoresistance, quantum interference effects, helical magnetic effects, and others. Currently, numerous transport phenomena in Dirac quantum materials remain poorly understood from a theoretical standpoint, such as linear magnetoresistance in weak fields, anomalous Hall effects in nonmagnetic materials, and three-dimensional quantum Hall effects. Studying these transport properties will not only deepen our understanding of Dirac quantum materials, but also provide important insights for their potential applications in spintronics and quantum computing. In this paper, quantum transport theory and quantum anomaly effects related to the Dirac equation are summarized, with emphasis on massive Dirac fermions and quantum anomalous semimetals. Additionally, the realization of parity anomaly and half-quantized quantum Hall effects in semi-magnetic topological insulators are also put forward. Finally, the key scientific issues of interest in the field of quantum transport theory are reviewed and discussed.