Spin Channel Research Articles

Control of the magnetic anisotropy and Curie temperature of monolayer 1T-CrTe2 for room temperature application

Magnetic units with large magnetic anisotropy energy (MAE) and high Curie temperature (Tc) are crucial for spintronic and quantum computing devices, which are a persisting demand for miniaturization of magnetic units. Using first-principles calculations and Monte Carlo simulation, it is found that monolayer 1T-CrTe2 exhibits strong perpendicular magnetic anisotropy with a MAE of approximately 5.29 meV and high Tc of ∼136 K. Interestingly, we find that the MAE and Tc of monolayer 1T-CrTe2 are tunable through electron/hole doping, strain, and heterostructure engineering. The magnetic easy-axis can be adjusted from out of plane to in plane, which is mainly attributed to the coupling between Te atomic orbitals (px, py). Second-order perturbation theory reveals that the spin–orbit coupling interaction between the occupied px and unoccupied py orbitals in opposite spin channel near Fermi level gives rise to negative contribution of MAE. Moreover, Tc can be enhanced to ∼230 K through super–superexchange mechanism of heterostructure due to the electron hopping between t2g/eg orbitals of Cr4+ ions and e1/a1 orbitals of Fe2+ ions. Importantly, we find that Tc can be boosted above room temperature by applying moderate strain (6%), ascribing to significant enhancement of MAE and exchange coupling constant. The present work indicates that monolayer 1T-CrTe2-based two-dimensional materials are very promising for room temperature application in magnetic storage and information processing.

Spintronic Quantum Phase Transition in a Graphene/Pb0.24Sn0.76Te Heterostructure with Giant Rashba Spin‐Orbit Coupling

AbstractMechanical stacking of two dissimilar materials often has surprising consequences for heterostructure behavior. In particular, a 2D electron gas (2DEG) is formed in the heterostructure of the topological crystalline insulator Pb0.24Sn0.76Te and graphene due to contact of a polar with a nonpolar surface and the resulting changes in electronic structure needed to avoid polar catastrophe. The spintronic properties of this heterostructure with non‐local spin valve devices are studied. This study observes spin‐momentum locking at lower temperatures that transitions to regular spin channel transport only at ≈40 K. Hanle spin precession measurements show a spin relaxation time as high as 2.18 ns. Density functional theory calculations confirm that the spin‐momentum locking is due to a giant Rashba effect in the material and that the phase transition is a Lifshitz transition. The theoretically predicted Lifshitz transition is further evident in the phase transition‐like behavior in the Landé g‐factor and spin relaxation time.

Strain-tuned full spin polarization and ndoping of phosphorene via the phosphorene/Co[formula omitted]Sn[formula omitted]S[formula omitted] heterojunction

Phosphorene’s desired bandgap, high carrier mobility and weak spin–orbit coupling qualify it as an exceptional semiconductor spin channel material. These traits underscore the importance of examining phosphorene’s electronic structure and that of half-metal heterojunctions (HJs) in innovating spintronic device design. This paper methodically investigates the electronic structure and Schottky barrier (SB) of a van der Waals HJ, comprising phosphorene and the half-metal Co3Sn3S2, subjected to biaxial mechanical strain via a first-principles method. The investigation unveils that phosphorene, as an n-type semiconductor, possesses substantial spin polarization. Remarkably, phosphorene undergoes three states – metallic, half-metallic, and semiconducting – subject to varying strain ratios (E). Furthermore, we discern that phosphorene’s spin polarization, peaking at 100% for −2%<E<1%, is tunable with strain. The SB heights (SBHs) also exhibit a consistent escalation with strain: for −5%≤E<1%, the electron SBH is 0 eV, which increments from 0.017 eV to 0.021 eV for 1%≤E≤3%. Intriguingly, the spin-down band alignment of the HJ transitions from type-II to type-I at E= 3%. Our Bader charge analysis validates that the n-doping of phosphorene is primarily due to electron acceptance from Co3Sn3S2. The orbital hybridizations between phosphorene and Co3Sn3S2 leads to complete spin polarization of phosphorene. Collectively, these observations confirm phosphorene’s capability to attain n-type doping with 100% spin polarization. Moreover, our findings suggest the possibility to modulate both the bandgap of phosphorene and the SBHs of the HJ with strain. This highlights the potential of the phosphorene/Co3Sn3S2 HJ in advancing the field of low-dimensional, flexible spintronics.

Structural, Elastic, Electronic, and Magnetic Properties of Nd‐Doped NaScGe Half‐Heusler Compound by Ab‐Initio Method

AbstractA comprehensive investigation is conducted on the electronic structure and magnetic properties of half‐Heusler NaScGe, which is doped with a rare earth element Nd with different concentrations. The Heusler Na1‐xNdxScGe (where x = 0, 0.25, 0.75, and 1) compounds are thoroughly investigated. The examination encompassed structural, elastic, magnetic, and electronic characteristics using the full potential linearized augmented plane wave (FP‐LAPW) method. Generalized gradient approximation (GGA) is used to calculate the structural parameters and electronic characteristics. The equilibrium lattice constant and band gap of half‐Heusler NaScGe are found to be in good accord with other data. The density of states (DOS) investigation has revealed a semiconductor behavior of half‐Heusler NaScGe and half‐metallic ferromagnetic properties of quaternary‐Heusler Na0.75Nd0.25ScGe, characterized by a moderate band gap in minority spin channel. In addition, the DOS analysis has shown that both ternary half‐Heusler NdScGe and QH Na0.25Nd0.75ScGe compounds have exhibited metallic ferromagnetic activity. The work has introduced a novel approach for producing half metals from the semiconductor half‐Heusler NaScGe. Quaternary‐Heusler Na0.75Nd0.25ScGe is identified as a promising material for applications spintronic.

Potential-tuned magnetic switches and half-metallicity transition in zigzag graphene nanoribbons

Realizing controllable room-temperature ferromagnetism in carbon-based materials is one of recent prospects. The magnetism in graphene nanostructures reported previously is mostly localized by breaking the local sublattice imbalance. Here, we predict a robustly potential-tuned ferromagnetic domain lying between the inter-chain carbon atoms inside the zigzag graphene nanoribbons. We show that the effective zigzag edges provide the strong correlation background through narrowing the band width, while the internal Van Hove filling (VHF) provides the strong ferromagnetic background inherited from the bulk. The induced ferromagnetism exhibit interesting switching effect when the nominal VHF crosses the intra- and inter-chain region by tuning the potential drops. We further observe a robust half-metallicity transition from one spin channel to another within the same magnetic phase. These novel properties provide promising ways to manipulate the spin degree of freedom in graphene nanostructures.

Engineering High-Spin State Cobalt Cations in Sulfide Spinel for Enhancing Water Oxidation.

The spin states of active sites have a significant impact on the adsorption/desorption ability of the reaction intermediates during the oxygen evolution reaction (OER). Sulfide spinel is not generally considered a highly efficient OER catalyst owing to the low spin state of Co3+ and the lack of unpaired electrons available for adsorption of reaction intermediates. Herein, it is proposed a novel Nd-evoked valence electronic adjustment strategy to engineer the spin state of Co ions. The unique f-p-d orbital electronic coupling effect stimulates the rearrangement of Co d orbital electrons and increases the eg electron filling to achieve high-spin state Co ions, which promotes charge transport by propagating a spin channel and generates a high number of active sites for intermediate adsorption. The optimized CuCo1.75 Nd0.25 S4 catalyst exhibits outstanding electrocatalytic properties with a low overpotential of 320mV at 500mAcm-2 and a 48h stability at 300mAcm-2 . In situ synchrotron radiation infrared spectra confirm the quick accumulation of key *OOH and *O intermediates. This work deepens the comprehensive understanding of the relationship between OER activity and spin configurations of Co ions and offers a new design strategy for spinel compound catalysts.

Ferrimagnetic half Heusler alloys for waste heat recovery application - First principle study using different exchange–correlation functionals

ZrMnSi and HfMnSi half Heusler alloys with magnetic ground state are investigated through density functional theory. The different exchange–correlation functionals (GGA, LDA, PBESol and WC) are used to study these alloys. The equilibrium lattice constants and corresponding ground state energies are calculated using these four approximation methods. From GGA functional, the obtained band gap for ZrMnSi is 1.268 eV and HfMnSi is 1.311 eV. The reported alloys are predicted to be half metals from different potentials, where those alloys show semiconductor character in minority spin channel and also exhibit metallic character in majority spin channel. The studied alloys are mechanically stable and ductile in nature. The total magnetic moment of −3μB is obtained in the reported ferrimagnetic alloys. The obtained thermoelectric figure of merit for ZrMnSi and HfMnSi is 0.46 at 1200 K and 0.31 at 1200 K respectively, it shows that these alloys are the potential candidates for waste heat recovery application, and they are also useful for spin flip device application.

Rare earth based MgPm2X4 (X = S, Se) spinel chalcogenides for spintronic and thermoelectric applications

In current report, the structural, magnetic, and thermoelectric properties of RE doped MgPm2X4 (X = S, Se) spinels were investigated. The energy difference in ferromagnetic and antiferromagnetic states reveals the stability of MgPm2(S/Se)4 in the ferromagnetic states. The computation of enthalpy of formation also ascertains thermodynamic stability of crystal structure. Spin-dependent band structure and density of states analysis reveal ferromagnetic semiconducting character showing different electronic behavior in both spin channels. The room temperature ferromagnetism, spin polarization and Curie temperature are estimated from exchange energies analysis. In addition, exchange constants (N0α and N0β), exchange energy Δx(pd), crystal field energy, and double exchange mechanism were studied to explore the magnetic response. Likewise, the electrical conductivity, thermal conductivity, Seebeck co-efficient, and power factor show effect on electrons spin and their potential for thermoelectric devices.

Study of curie temperaure, spin polarization, ferromagnetism and transport behavior of Ba2CrXO6 (X = Ta, W, Re, Os) for spintronic

The double perovskites (DPs) have become emerging aspirant for spintronic technology because of their stable, and multifunctional properties. Here in present article, the role 5d-electrons of Ta, W, Re, and Os in ferromagnetism, and thermoelectric behavior has been illustrated briefly. The ideal values of tolerance factor, formation energy and phonons dispersions are reported for structural, thermodynamic, and lattice dynamic stabilities. The higher Curie temperature and spin polarization has been addressed by Heisenberg model and spin density calculations. The ferromagnetism has been explained by the metallic and insulating channels of spin up and spin down configuration through hybridization, exchange energies, and exchange constants. The shifting of magnetic moments from Cr and X sites to Ba, O and interstitial sites ensures the exchange coupling due to spin of electrons rather than clustering. Furthermore, thermoelectric effect on the spin degree of electrons and transport characteristics are calculated by BoltzTraP code.

Symmetry-driven half-integer conductance quantization in Cobalt–fulvalene sandwich nanowire

Precise manipulation and monitoring spin transport in one-dimensional (1D) systems is a long-sought goal in the field of nano-spintronics. Based on first-principles calculations, we report the observation of half-integer conductance quantization in the Cobalt-fulvalene sandwich nanowire. Compared with a pure monatomic Cobalt wire, the introduction of fulvalene molecules leads to three important features: Firstly, the strong coupling between the fulvalene and the Cobalt prevents the contamination of the ambient air, ensuring both chemical and physical stabilities; Secondly, the fulvalene symmetry-selectively filters out most of the d-type orbitals of the Cobalt while leaving a single d-type orbital to form an open spin channel around the Fermi level, which offers a mechanism to achieve the observed half-integer conductance; Thirdly, it maintains a superexchange coupling between adjacent Co atoms to achieve a high Curie temperature. Spin transport calculations show that this half-metallic nanowire can serve as a perfect spin filter or a spin valve device, thus revealing the potential of Cobalt-fulvalene sandwich nanowire as a promising building block of high-performance spintronics technology.

Chemically Controlled Reversible Magnetic Phase Transition in Two-Dimensional Organometallic Lattices.

Developing an efficient method to reversibly control materials' spin order is urgently needed but challenging in spintronics. Though various physical field control methods have been advancing, the chemical control of spin is little exploited. Here, we propose a chemical means for such spin manipulation, i.e., utilizing the well-known lactim-lactam tautomerization to reversibly modulate the magnetic phase transition in two-dimensional (2D) organometallic lattices. The proposal is verified by theoretically designing several 2D organometallic frameworks with antiferromagnetic to ferrimagnetic spin order transformation modulated by lactim-lactam tautomerization on organic linkers. The transition originates from the change in spin states of organic linkers (from singlet to doublet) via tautomerization. Such a transition further switches materials' electronic structures from normal semiconductors with zero spin polarization to bipolar magnetic semiconductors with valence and conduction band edges 100% spin polarized in opposite spin channels. Moreover, the magnitude of magnetic anisotropy energy also enhances by 5- to 9-fold.

Bipolar ferromagnetic semiconductors and dipole-modulated magnetism in two-dimensional Janus transition metal dihalides

Two-dimensional (2D) transition metal dihalides (TMDHs) have attracted great interest owing to their unique magnetic and semiconductor properties. Compared with the mirror/inversion symmetric materials, 2D Janus materials possess vertical intrinsic dipole moment, which offer a versatile platform for the fundamental physics and future spintronic devices. Here, we systematically explore the magnetic and electronic properties of the 2D Janus transition metal dihalides MXY (M = Co and Ni; X ≠ Y = Cl, Br, and I) monolayers and bilayers by using density functional theory. The monolayer CoClBr, NiClBr, and NiBrI are bipolar ferromagnetic semiconductors that possess the valence and conduction band edges of different spin channels. The magnetism of the bilayer CoClBr, NiClBr, and NiBrI is highly dependent on the accumulated dipole moments of the two adjacent layers. When the dipole moments in both layers are aligned in the same direction and the accumulated dipole moments are nonzero, the systems are antiferromagnetic half semiconductors. However, when the dipole moments in the two layers are opposite and the accumulated dipole moments are zero, the systems are A-type antiferromagnetic semiconductors. Our findings are helpful to understand the magnetism of Janus TMDHs and guide experiments in exploring their potential application in spintronic devices.

Double stranded antiferromagnetic helix as an efficient spin filter

We report a large degree of spin filtration in a double stranded (ds) antiferromagnetic helix (AFH) system. Generally spin channel separation is not possible when a magnetic system possesses a vanishing net magnetization. But we show that a highly polarized spin current can be obtained through the ds AFH when it is subjected to a transverse electric field. Describing the physical system within a tight-binding framework, spin-dependent transport phenomena are studied using the well known Green’s function formalism. The effects of chirality (left-handed and right-handed), electric field, electronic hopping (short-range and long-range) in each strand, system temperature, and size of the helix on spin filtration are critically investigated. Two different configurations of magnetic moments in the helix are taken into account, for a more general description. Suitably adjusting the physical parameters, almost cent percent spin polarization can be substantiated and that feature persists even for a broad parameter range. Our analysis may open up a new direction for achieving spin-selective electron transmission and designing of controlled spintronic devices using similar kinds of fascinating helical magnetic systems.

(Invited) Understanding the Role of Dopants (Al, Zn, Zr) in Altering Charge-Storage Capacity and Cycling Profiles of VFe2Ox

Vanadium ferrite (VFe2Ox) is a defective spinel system that can incorporate substantial Li+ and exhibits a high charge–discharge rate, particularly when structured as a nanoscale aerogel.1 Cations such as Zr, Zn and Al,2 can readily enter the structure substitutionally and have strong, but differing effects on the charge-storage capacity of the material. These earth abundant, cost- effective constituent elements give this class of materials strong potential as future Li-ion battery cathodes but optimizing the stoichiometry for maximum capacity and stability will require understanding the redox sequence of the host cations (Fe, V) and role of intentional dopants.We use density functional theory calculations in concert with in situ and operando X-ray absorption near-edge spectroscopy (XANES) spectra obtained using an in-lab X-ray absorption spectrometer to uncover the quantum mechanical-level effects that underpin relevant energy- storage behaviors of doped and undoped VFe2Ox. Our experimental V K-edge and Fe K-edge spectra indicate reduction of both species during discharge but cannot distinguish between tetrahedral and octahedral Fe redox sites or fully resolve the valency of each element as a function of state of charge. Using a hybrid form of density functional theory that accounts for the strong correlation present in 3d elements, we show that both V and Fe are indeed reduced, but that only tetrahedral Fe is redox active until fully converted to Fe2+. Furthermore, both octahedral and tetrahedral Fe3+ are high spin configuration, but the 5μB moments in the fully filled majority spin channel at each symmetry site are anti-aligned. This arrangement allows for easy exchange of electrons and facilitates conduction. We also calculate XANES spectra based on first principles calculations to be compared directly to those measured in the lab. This cross- check allows us to understand the effect of Al, Zr, and Zn dopants on the redox sequence and relate these results to site preference and capacity. Our combined experimental and calculational investigation sheds light on how these complex materials store Li ions and points toward future alterations that may further improve their properties.

Gate-Tunable Spin Seebeck Effect and Pure Spin Current Generation in Molecular Junctions Based on Bipolar Magnetic Molecules.

Generating pure spin currents is very desirable in spintronics, as it provides a promising way to substantially reduce Joule heating and achieve ultrahigh integration density. However, to date, most spintronic devices exhibit spin currents that are accompanied by charge currents. The generation of pure spin currents on the nanoscale, particularly at the single-molecule level, remains challenging. Here, we propose that by exploiting our recently reported bipolar magnetic molecules (BMMs) as the core component of single-molecule devices, where the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) come from different spin channels, the generation of pure spin currents can be easily realized via the spin Seebeck effect (SSE) with applied temperature gradient. Moreover, the spin Seebeck coefficient can be modulated over a wide range by applying an external gate voltage. The proposal is verified through first-principles calculations on two BMM-based molecular junctions.

Magnetic second-order topological physics in two-dimensional NiZrI6

Two-dimensional (2D) nonmagnetic second-order topological insulators (SOTIs) have been exhaustively studied, whereas 2D magnetic SOTIs have received little attention from researchers. In this work, we have demonstrated using first-principles calculations that the 2D NiZrI6 monolayer is a 2D magnetic SOTI with a ferromagnetic ground state. Two spin channels in the 2D NiZrI6 monolayer exhibit nontrivial gaps. According to the higher-order bulk-boundary correspondence, the 2D NiZrI6 monolayer shows topologically protected corner states with quantized fractional charge (e/3) that are spin-polarized and pinned at the sample's corners in real space. In addition, the zero-dimensional corner states of the 2D NiZrI6 monolayer are resistant to spin–orbit coupling (SOC) effects. It is anticipated that 2D NiZrI6 monolayer with magnetic higher-order topology will contribute to topo-spintronics advancement.

First-principles investigation of structural, electronic, optical, and magnetic properties of a scintillating double perovskite halides (Cs[formula omitted]LiCeX[formula omitted]) with (X = F, Br, and I)

In this study, several physical properties (structural, electronic, magnetic, and optical) of a scintillating double perovskite halide Cs2LiCeX6 (X = F, Br, and I) are investigated using the density functional theory (DFT) within the Wien2k code. The optimized lattice parameter (a0) of Cs2LiCeBr6 agrees perfectly with the experimental results. The optimized ground state energy appears to confirm the cubic stability. The band structure and densities of states are explored using PBE-GGA coupled with Tb-mBJ approximation. In the spin-up channel, the compound Cs2LiCeX6 (X = F, Br, and I) has a Fermi level occupied, with a band gap of 1.966eV, 1.350eV, and 1.184eV, respectively. While in the spin-down channel, the double perovskite halide Cs2LiCeBr6 and Cs2LiCeI6 behave like a semiconductor, with a band gap of 3.293eV and 2.418eV, respectively. The asymmetric density of states in both spin channels and the optimized energy volume curve in spin-polarized calculation assert to the ferromagnetic nature. The optical properties are calculated, and it is revealed that Cs2LiCeBr6 and Cs2LiCeI6 has a high optical conductivity than Cs2LiCeF6. The absorption in the ultraviolet and gamma frequency range, along with the emittance in the visible light unlocks the door for various applications, like medical imaging, radiation detection and particle detection.

Structural, electronic, optical, mechanical and magnetic properties of Co2CrZ (Z = As, B, Ga, Pb) full-Heusler compounds

Two separate computational algorithms have been used in the current investigation of Full-heusler compounds. One is the pseudo-potential approach used in the Atomistic Tool Kit-Virtual Nanolab, while the other is FP-LAPW method as implemented in WIEN2k. In the computational code, these compounds exhibit mattelic character in both the majority and minority spin channels. According to the WIEN2k and ATK-VNL codes, the computed magnetic moments of these compounds Co2CrZ (Z = As, B, Ga, and Pb) are 4.93 µB and 5.02 µB, 3.00 µB and 3.08 µB, 3.02 µB and 3.16 µB, and 4.07 µB and 4.30 µB, respectively. Between the estimated value and the Slater-Pauling rule, we discovered excellent agreement. These compounds' optical characteristics include reflectivity, refractive index, excitation coefficient, and absorption coefficient, among others. An analysis has been done on the electron energy loss and optical conductivity. Both the electron energy-loss function and the absorption coefficient increase as the energy value increases. As per the results of elastic properties, Co2CrZ compounds with Z = As, Pb are ductile by nature, whereas those with Z = B, Ga are brittle. Co2CrZ (Z = As, B, Ga, and Pb) compounds exhibit metallic behaviour when their Cauchy pressure (CP = C12 - C44) value is positive.

Magnetic Second-Order Topological Insulators in 2H-Transition Metal Dichalcogenides.

The transition metal dichalcogenides, 2H-VX2 (X = S, Se, Te), are identified astwo-dimensional second-order topological insulator (SOTI) with a ferromagnetic ground state by first-principles calculations. The 2H-VX2 (X = S, Se, Te) materials have a nontrivial band gap in two spin channels is found and exhibit topologically protected corner states with spin-polarization. These corner states only accommodate the quantized fractional charge (e/3). And the charge is bound at the corners of the nanodisk geometry 2H-VX2 (X = S, Se, Te) in real space. The corner states are robust against symmetry-breaking perturbations, which makes them more easily detectable in experiments. Further, it is demonstrated that the SOTI properties of 2H-VX2 (X = S, Se, Te) materials can be maintained in the presence of spin-orbit coupling and are stable against magnetization. Overall, the results reveal 2H-VX2 (X = S, Se, Te) as an ideal platform for the exploration of magnetic SOTI and suggest its great potential in experimental detection.

DFT insight into magnetoelectronic and optical properties of Mo-modified BaTiO3

Herein, the magnetoelectronic and optical characteristics of Ba1-xMoxTiO3 (x = 25%, 50%, and 75%) compound are computed by employing density functional theory (DFT). The robust half metallic ferromagnetic (HMF) character has been observed for Mo-incorporated BaTiO3. This behavior of Mo-modified BaTiO3 is due to the highly asymmetric behavior in both spin channels, semiconducting in dn-spin and metallic nature in up-spin version. The computed total magnetic moment (MTot) is found to be 4.0 μB for all substitutional concentrations which is mainly due to the Mo-4d states. In addition, the optical parameters (extinction coefficient, reflectivity, optical conductivity, refractive index, dielectric function, and absorption coefficient) are also calculated. The computed results suggest the suitability of studied material for spintronic and optoelectronic devices.