Spin-up States Research Articles

Impact of composition on the properties of full-Heusler Ti2FexMn1-xAl alloys in spintronics

This study explores the structural, electronic, and magnetic characteristics of full-Heusler Ti2FexMn1-xAl alloys for spintronic applications. The regular Heusler structure is identified as the most stable across all x concentrations. The inverse Heusler structure exhibits half-metallic behavior with a finite energy band gap in the spin-up states, while the regular structure shows metallic behavior for both spin directions. Dirac-like points along the M→Γ direction are observed, particularly in alloys with x = 0 and 0.25 (inverse structure) and x = 0.5, 0.75, and 1 (regular structure), indicating advanced electronic properties. Magnetic analysis reveals that Ti atoms' local magnetic moments are antiparallel to those of Mn and Fe atoms. The total magnetic moment is highest for x = 1 (Ti2MnAl) and nearly zero for x = 0 (Ti2FeAl). Additionally, the inverse Heusler structure achieves 100 % spin polarization at the Fermi energy, underscoring its suitability for spintronic applications. This study highlights the potential of Ti2FexMn1-xAl alloys for future spintronic devices.

Controlling Ultrafast Magnetization Dynamics via Coherent Phonon Excitation in a Ferromagnet Monolayer.

Exploring ultrafast magnetization control in 2D magnets via laser pulses is established, yet the interplay between spin dynamics and the lattice remains underexplored. Utilizing real-time time-dependent density functional theory (rt-TDDFT) coupled with Ehrenfest dynamics and nonadiabatic molecular dynamics (NAMD) simulations, we systematically investigate the laser-induced spin-nuclei dynamics with pre-excited A1g and E2g coherent phonons in the 2D ferromagnet Fe3GeTe2 (FGT) monolayer. Selective pre-excitation of coherent phonons under ultrafast laser irradiation significantly alters the local spin moment of FGT, consequently inducing additional spin loss attributed to the nuclear motion-induced asymmetric interatomic charge transfer. Excited spin-resolved charge undergoes a bidirectional spin-flip between spin-down and spin-up states, characterized by a subtle change in the spin moment within approximately 100 fs, followed by unidirectional spin-flip, which will further contribute to the spin moment loss of FGT within tens of picoseconds. Our results shed light on the coupling of coherent phonons with magnetization dynamics in 2D limit.

Alkali-based half metals as sustainable materials for spin electronics and energy harvesting application — Materials computation

The structural, mechanical, electronic, magnetic, and thermoelectric properties of alkali-based half-Heusler alloys (LiCrGe, LiCrSn, and LiCrPb) are investigated using the Wien2k code. These alloys exhibit half-metallic behavior in both ferromagnetic and antiferromagnetic phases. A phase transition from a stable ferromagnetic phase to a more stable antiferromagnetic phase indicates ductility. In the antiferromagnetic phase, using GGA exchange–correlation functional with 10,000 K-points, a band gap is observed in the spin-up state, with band gap energies of 0.9367 eV, 0.7762 eV, and 0.7913 eV, respectively. The alloys have a spin magnetic moment of −3μB, consistent with the Slater–Pauling rule. They also exhibit high Curie temperatures and 100% spin polarization in the spin-down state. The alloys LiCrZ (Z = Ge, Sn, Pb) shows promising thermoelectric behavior. Using the BolzTrap package, we observed, high Seebeck coefficient, electrical conductivity, low thermal conductivity, and enhanced power factor. The p-type LiCrZ (Z = Ge, Sn, Pb) compounds show thermoelectric figure of merit of 0.52, 0.76, and 0.84 at 1200 K, while n-type compounds have figure of merit of 0.56, 0.65, and 0.80 at the same temperature. These properties make these materials promising for spintronic and thermoelectric applications.

Chromium nano-segregation and intermediate band formation in heavily-doped ZnS:Cr films

X-ray absorption spectroscopy, X-ray diffraction, and UV–Vis spectroscopy were employed to investigate heavily-doped ZnS:Cr films prepared by RF magnetron co-sputtering. EDS indicates ca. 5 at. % Cr incorporation as well as slight S-deficiency. XAS in the Zn K- and Cr K-edges revealed Zn-by-Cr substitution and segregation of Cr nanoclusters which lead to significant lattice distortion. XRD indicates a 44 % increase in the strain, an increase in the lattice parameter, and a decrease in the crystallite size upon Cr incorporation. The presence of Cr nanoclusters contributed to changes in the band gap, a large Urbach tail parameter of 565 meV, and the formation of an intermediate band arising from the Cr 3d spin-up states. The results suggest ZnS:Cr films in the heavily doping regime could lead to applications in photovoltaics and spintronics.

Computational Investigation on Cr-Doped Sc2CO2 MXene under Strain for Electronic Properties, Quantum Capacitance, and Photocatalytic Activity.

Sc2CO2 MXene has potential applications in energy storage and optoelectronics due to its superior structure and excellent properties. The electronic properties, quantum capacitance, and photocatalytic activity of Cr-doped Sc2CO2 under strain are studied by the density functional theory. Cr doping makes the system produce magnetism. The spin-down states of Sc2CO2-Cr under strain are direct semiconductors, while their spin-up states are indirect semiconductors. Sc2CO2-Cr under +5, -5, -3, and -2% strains in an aqueous system are suitable for cathode material. A large voltage drastically modulates the type of electrode materials. Sc2CO2-Cr under strains from 0 to +2% can perform the oxygen evolution reaction at an alkaline environment, while the Sc2CO2-Cr system under strain is a good for CO2 photocatalysis at pH 0 and 7.

Spin-polarized second-order nonlinear Hall effect in 8-Pmmn monolayer borophene

The second-order nonlinear Hall effect in 8-Pmmn monolayer borophene under the influence of an out-of-plane electric field and intrinsic spin–orbit interaction is reported. This unconventional response sensitive to the breaking of discrete and crystal symmetries can be tuned by the applied electric field, which can vary the bandgap induced by spin–orbit coupling. It is described by a Hall conductivity tensor that depends quadratically on the applied electric field. We find that the nonlinear Hall effect strongly depends on the spin polarization. In particular, it exhibits out of the phase character for spin-up and spin-down states. Remarkably, it undergoes a phase flip in the spin-up state at a large out-of-plane electric field that generates a staggered sublattice potential greater than the spin–orbit interaction strength. It is shown that the nonlinear Hall effect in the system originates from the broken inversion symmetry that plays an indispensable role in developing finite Berry curvature and its relevant dipole moment. It is found that at zero temperature, the nonlinear Hall response is maximal when the Fermi energy is twice the bandgap parameter and vanishes at large Fermi energies. Notably, the peak of nonlinear Hall response shifts to lower Fermi energies at finite temperature.

The chiral dependence of effective masses of polaron spin states in chiral structures

The renormalization of effective masses of polaron spin states in chiral structures is studied based on the direct spin–phonon coupling, in which the simple formulas for the renormalization of effective masses are derived for polarons with spin-up and spin-down states using a linear-combination operator method. The theoretical calculations show that the effective masses are renormalized significantly with increasing the cut-off wave vector of phonon modes and the renormalized magnitudes are different for right-handed and left-handed structures. Moreover, the renormalized magnitude for the spin-down state is larger than the spin-up one. This asymmetrical behavior naturally gives rise to very different conductivities for spin-up and spin-down states as electrons transmitted through the systems. These results not only enrich the microscopic origin of CISS mechanism, but also enlighten more experimental ways to explore CISS.

Li-decorated B12C6N6 hybrid nanocage for sensing Cl2, COCl2, H2S and NH3 gas molecules

We examined the gas sensing abilities of Li-decorated B12C6N6 (B12C6N6Li) hybrid nanocage, introducing B12C6N6 for the first time in sensing applications. The toxic gas molecules like Cl2, COCl2, H2S, and NH3 were considered. The B12C6N6 nanocage with C2V symmetry displayed the lowest energy among its isomers. Li exhibited stronger anchoring above B3C2N ring compared to B2C2, B2N2, and B3CN2 rings of B12C6N6 nanocage, displaying a binding energy of −3.30 eV. Li decoration resulted in asymmetric spin-up and spin-down states near Fermi level, indicating magnetic nature of complexes. B12C6N6, an electron-deficient nanocage, displayed charge transfer from Li atom to the nanocage. Substantial changes in electronic states occurred following the adsorption of Cl2 and COCl2 molecules. COCl2, H2S, and NH3 adsorption is thermodynamically favourable over a wide temperature and pressure range, while Cl2 adsorption is favourable only within a confined range. Earlier findings indicate dissociative adsorption of Cl2 on nanocages rendering the substrate to be non-reusable. B12C6N6Li considered here is superior over other nanocages as Cl2 adsorbs in molecular form while B12C6N6Li also demonstrates significant sensitivity. B12C6N6Li nanocage is unsuitable for sensing H2S and NH3 gas molecules but holds promise as a potential candidate for sensing Cl2 and COCl2 gas molecules.

Inducing d 0 magnetism in new SrCl2 monolayer towards spintronic applications

Magnetism engineering in two-dimensional (2D) materials has been widely explored to make new spintronic materials. In this work, the doping (with alkali metals at Sr sublattice and with chalcogen atoms at Cl sublattice) method are proposed to induce significant d 0 magnetism in the non-magnetic SrCl2 monolayer. This 2D material is an indirect gap insulator with large band gap of 4.97(6.25) eV as obtained by PBE(HSE06) functional, exhibiting ionic character that is generated by the charge transfer from Sr atom to Cl atoms. The monolayer is significantly magnetized by doping with alkali metals, where a total magnetic moments between 0.90 and 1.00 μ B are obtained. Herein, Cl atoms closest to the doping site make main contribution to the system magnetism. Interestingly, the doped systems exhibit half-metallic behavior that is generated by semiconductor spin-up state and metallic spin-down state. On the other hand, the diluted magnetic semiconductor nature emerges in SrCl2 monolayer as a result of doping with chalcogen atoms. In these cases, total magnetic moment of 1.00 μ B is obtained, where magnetic properties are produced mainly by chalcogen impurities and Cl atoms below them. The electronic and magnetic properties of the doped systems are regulated mainly by the outermost p orbital of Cl and chalcogen atoms, and Sr-4d orbital that form mainly the conduction band. Upon further increasing the doping level of K and O atoms, the half-metallic or magnetic semiconductor natures are preserved. Results presented in this work may introduce new prospective 2D spintronic candidates for spintronic applications, which are derived from a non-magnetic SrCl2 monolayer via doping with d 0 atoms.

Optically-modulated edge states and resonant tunneling based on valley-Zeeman spin–orbit coupling

The valley-Zeeman spin–orbit coupling (VZSOC) in graphene provides a platform to discover novel edge states and enrich the quantum transport phenomena. In this work, based on the VZSOC induced helical edge states regarded as two copies of chiral edge states, we investigate the modulation of the edge state and corresponding resonant tunneling with the well-defined transmission peaks under off-resonant circularly polarized (ORCP) light. It shows that the spin-up or spin-down chiral edge state can be transformed into two types of antichiral edge state where the edge states propagate in the same direction at two parallel boundaries and the bulk states propagate in opposite direction, and reversed chiral edge states by the intensity and polarized direction of the ORCP light, finally leading to fascinated edge states. These edge-state transitions are attributed to regulating the Dirac gaps by the ORCP light. Particularly, some novel resonant tunneling in junctions consisting of different edge states are discovered, most of which can be intuitively understood as different types of the loop currents that the current flows in a loop. Interestingly, the combined effect of the backscattering and loop current also plays an important role in generating resonant tunneling. These results provide a new view to manipulate helical edge state induced by the VZSOC and understand rich physics of the resonant tunneling by the loop current.

Investigation of structural and electronic properties of double perovskites A2LnRuO6 (A = Ba, Ca; Ln = Eu, Dy)

Using density functional theory, we investigated the structural, vibrational, and electronic properties of A2LnRuO6 (A = Ba, Ca; Ln = Eu, Dy) double perovskite oxides using GGA and GGA+U exchange-correlation approximations. Ba2LnRuO6 double perovskites exhibit a structure with cubic ( Fm3¯m ) symmetry, whereas Ca2LnRuO6 compounds have monoclinic (P21/n) symmetry. Raman spectroscopy analysis shows stability and the presence of A1g , E g and 2F2g modes for Ba2LnRuO6, while for Ca2LnRuO6, the observed Raman active modes are A g and B g . A2LnRuO6 shows semiconducting nature with an electronic band gap in the range of 1.3 eV-3.27 eV with GGA+U calculations. The spin-polarized calculations indicate the presence of strong magnetic behaviour with magnetic moment equal to 3 μ B /unit cell for Ba2LnRuO6 and 6 μ B /unit cell for Ca2LnRuO6. The spin-up and spin-down states show different band gap values so these compounds can be useful for applications in spintronics and magnetic memory devices.

Adsorption of N, He and Ne on CGe nanoribbons for sensing and optoelectronic applications.

Research into nanomaterials yields numerous exceptional applications in contemporary science and technology. The subject of this investigation is a one-dimensional nanostructure, six atoms wide, featuring hydrogen-functionalized edges. The theoretical foundation of this study relies on Density Functional Theory (DFT) and is executed through the utilization of the Vienna Ab initio Simulation Package (VASP). The outcomes demonstrate the stability of adsorption configurations, along with the preservation of a hexagonal honeycomb lattice. The pristine configuration, characterized by a wide bandgap, is well-suited for optoelectronic applications, whereas adsorption configurations find their application in gas sensing. Nitrogen (N) adsorption transforms the semiconducting system into a semimetallic one, with the spin-up state showing semiconductor characteristics and the spin-down state exhibiting metallic attributes. The intricate multi-orbital hybridization is explored through the analysis of partial states. While the pristine system remains non-magnetic, N adsorption introduces a magnetic moment of 0.588 μB. The examination of charge density differences indicates a significant charge transfer from N to the CGe substrate surface. Optical properties are systematically investigated, encompassing the dielectric function, absorption coefficient and electron-hole density. Notably, the real part of the dielectric function exhibits negative values, a result that holds promise for future communication applications.

Study of the spin-polarized electronic, exchange constant, and thermoelectric characteristics of spinels LiFe2(O/S)4 for spintronic and energy-harvesting applications

Spintronics is a rapidly developing field in advanced technology. It focuses on manipulating the spin of electrons to achieve high-speed data transfer, handling, and storage in order to enhance its capabilities. We conducted a systematic investigation of the ferromagnetism, electronic, and thermoelectric characteristics of spinel compounds LiFe2(O/S)4. Our analysis for optimization demonstrates that ferromagnetic states exhibit great energy release compared to the antiferromagnetic states, indicating the presence of ferromagnetic behavior in the studied compounds. To evaluate the presence of ferromagnetism above room temperature, we employ the Heisenberg model to calculate the Curie temperature and spin polarization to evaluate the presence of ferromagnetism above room temperature. Additionally, a concise overview of the nature of ferromagnetism, including band structures, density of states, exchange energies and constants, hybridization double exchange model, and crystal-field energy, is provided in this research. The absorption of a shift in magnetic moment from Fe to the Li and O/S sites suggests that the ferromagnetic behavior is primarily due to the spin of electrons. Furthermore, we explore the impact of the thermal parameters on the electro-spin as well as the thermoelectric characteristics for both spin-down and spin-up states, providing insights into the energy-harvesting potential.

Computational study of half-metallic behavior, optoelectronic and thermoelectric properties of new XAlN3 (X = K, Rb, Cs) perovskite materials

In this study, we systematically explored the properties of novel perovskite materials, XAlN3 (X = K, Rb, and Cs), based on first-principles calculations and semiclassical Boltzmann transport theory. Generalized gradient approximation and HSE06 hybrid functional methods were used to investigate the electronic band structures. Our findings indicated intriguing half-metallic behavior where the spin-down state had metallic characteristics, whereas the spin-up state behaved as an insulator for all compounds, with indirect band gaps. These compounds had a significant magnetic moment of 5 μB, which confirmed their half-metallic nature. Analysis of the elastic constants indicated distinctive mechanical properties. Moreover, the dielectric functions indicated efficient energy absorption across a broad energy spectrum, which is particularly beneficial for ultraviolet optoelectronic applications. At 300 K with a chemical potential (μ) of +1.37 eV, CsAlN3 had a notable thermoelectric figure of merit (ZT) of 0.99. This ZT value remained competitive at 0.97, even at a high temperature of 1000 K in the p-type region. However, the ZT and Seebeck coefficients decreased in a temperature-dependent manner to affect the thermoelectric characteristics of these materials. Overall, our findings suggest that XAlN3 (X = K, Rb, and Cs) perovskite materials are promising candidates for use in various applications in spintronics, optoelectronics, and thermoelectric devices.

Ab initio investigations of the structure-stability, mechanical, electronic, thermodynamic and optical properties of Ti2FeAs Heusler alloy.

In this study, we employed density functional theory coupled with the full-potential linearized augmented plane-wave method (FP-LAPW) to investigate the structural, electronic, and magnetic properties of the Ti2FeAs alloy adopting the Hg2CuTi-type structure. Our findings demonstrate that all the examined structures exhibit ferromagnetic (FM) behaviour. By conducting electronic band structure calculations, we observed an energy gap of 0.739 eV for Ti2FeAs in the spin-down state and metallic intersections at the Fermi level in the spin-up state. These results suggest the half-metallic (HM) nature of Ti2FeAs, where the Ti-d and Fe-d electronic states play a significant role near the Fermi level. Additionally, the obtained total magnetic moments are consistent with the Slater-Pauling rule (Mtot = Ztot - 18), indicating 100% spin polarization for these compounds. To explore their optical properties, we employed the dielectric function to compute various optical parameters, including absorption spectra, energy-loss spectra, refractive index, reflectivity, and conductivity. Furthermore, various thermodynamic parameters were evaluated at different temperatures and pressures. The results obtained from the elastic parameters reveal the anisotropic and ductile nature of the Ti2FeAs compound. These findings suggest that Ti2FeAs has potential applications in temperature-tolerant devices and optoelectronic devices as a UV absorber.

Adsorption and solar light activity of noble metal adatoms (Au and Zn) on Fe(111) surface: a first-principles study.

Noble metals such as gold (Au), zinc (Zn), and iron (Fe) are highly significant in both fundamental and technological contexts owing to their applications in optoelectronics, optical coatings, transparent coatings, photodetectors, light-emitting devices, photovoltaics, nanotechnology, batteries, and thermal barrier coatings. This study presents a comprehensive investigation of the optoelectronic properties of Fe(111) and Au, Zn/Fe(111) materials using density functional theory (DFT) first-principles method with a focus on both materials' spin orientations. The optoelectronic properties were obtained employing the generalized gradient approximation (GGA) and the full-potential linearized augmented plane wave (FP-LAPW) approach, integrating the exchange-correlation function with the Hubbard potential U for improved accuracy. The arrangement of Fe(111) and Au, Zn/Fe(111) materials was found to lack an energy gap, indicating a metallic behavior in both the spin-up state and the spin-down state. The optical properties of Fe(111) and Au, Zn/Fe(111) materials, including their absorption coefficient, reflectivity, energy-loss function, refractive index, extinction coefficient, and optical conductivity, were thoroughly examined for both spin channels in the spectral region from 0.0 eV to 14 eV. The calculations revealed significant spin-dependent effects in the optical properties of the materials. Furthermore, this study explored the properties of the electronic bonding between several species in Fe(111) and Au, Zn/Fe(111) materials by examining the density distribution mapping of charge within the crystal symmetries.

Torque-dependent orbital modulation of X-ray pulsar Cen X-3

ABSTRACT Cen X-3 shows alternate spin-up/spin-down episodes lasting for tens of days. We study the orbital profiles and spectra of Cen X-3 during these spin-up/spin-down intervals, using long-term data monitored by Fermi/Gamma-ray Burst Monitor (GBM), Swift/Burst Alert Telescope (BAT), and Monitor of All-sky X-ray Image (MAXI)/Gas Slit Camera (GSC). In spin-up intervals, its orbital profile in 2–10 keV is symmetrically peaked around orbital phase 0.42, while in spin-down intervals of similar fluxes and similar magnitudes of spin change rate, its profile reaches a peak around orbital phase 0.22 and then declines gradually. Such a distinct orbital difference between spin-up and spin-down states of similar flux is hard to explain in the standard disc model and indicates that its torque reversals are related to processes on the orbital scale. The durations of continuous spin-up/spin-down trend (tens of days) also point to a superorbital variation. One possible scenario is the irradiation-driven warping disc instability, which may produce a flipped inner disc for tens of days.

Defect engineered magnetism induction and electronic structure modulation in monolayer MoS2

The electronic, magnetic, and optical characteristics of a defective monolayer MoS2 were examined by employing density functional theory (DFT)-based first-principles calculations. The effects of several defects on the electrical, magnetic, and optical properties, including Mo vacancies, MoS3 vacancies, and the substitution of a single Mo atom by two S atoms were studied in this work. Our first-principles calculations revealed that different types of defects produced distinct energy states within the band gap, leading to a band gap reduction after the introduction of various types of defects, which caused a change from semiconducting to metallic behavior. The spin-up and spin-down states were separated in the case of MoS3 vacancy. The total magnetization was ∼ −0.83 μB/cell, and the absolute magnetization was ∼ 1.23 μB/cell. Moreover, spin-up states had a 0.45 eV band gap, whereas spin-down states were metallic. Consequently, it can be promising for spin filter applications. It was disclosed that the broadband part of the electromagnetic spectrum has a high absorption coefficient, which is necessary for applications including impurity detection, photodiodes, and solar cells. Designing spintronic and optoelectronic devices will benefit from the modification of the electrical, optical, and magnetic properties by defect engineering of MoS2 monolayers presented here.

Ultrahigh spin filter efficiency and large spin Seebeck polarization of binuclear manganese phthalocyanine molecular junctions on nickel electrodes

In this paper, we investigated the spin transport properties of binuclear manganese phthalocyanine (Mn2Pc2) spintronic devices sandwiched between two nickel electrodes using the non-equilibrium Green's function method in combination with density functional theory. Based on the calculation results, the Mn2Pc2 device exhibited excellent spin-filtering capabilities, demonstrating an exceptionally high spin filter efficiency (SFE). Irrespective of the parallel or antiparallel orientation of magnetization in the electrodes, we observed that when both manganese atoms were in a spin-up state, the SFE of spin-resolved currents under finite bias and the thermoelectric currents induced by temperature gradients at fixed temperatures were both close to 100%. The large spin Seebeck polarization of the Mn2Pc2 device was also obtained at low reference temperatures. This study explores the potential for developing multifunctional spintronic single-molecule devices using Ni−Mn2Pc2.

Hybrid Functional Study on Electronic and Optical Properties of the Dopants in Anatase TiO2.

TiO2 was known as a golden heterogeneous photocatalyst due to its chemical stability, low cost, nontoxicity, and strong oxidizing power. However, anatase TiO2 predominantly absorbs the photon energy in the ultraviolet region (λ < 387.5 nm); therefore, to increase the utilization of sunlight, the approach of doping of metals and nonmetals into pure TiO2 is implemented. Here we incorporate the dopants of Zr, Si, V, W, Ge, Cr, Sn, Mo, and Pb into the TiO2 lattice and study the optoelectronic properties, including the formation energies and the electron charge distributions, using the Vienna ab initio Simulation Package (VASP) from the hybrid functional of Heyd, Scuseria, and Erhzerhof (HSE06). We observed that V-, Mo-, and Cr-doped systems introduce shallow impurity states within the band gap, and those states influence the shift of the absorbance spectra to visible light by enhancing the photocatalytic efficiency. W-doped anatase TiO2 structure reduces the band gap of the pure anatase TiO2 by 0.7 eV. Notably, this reduction occurs without the introduction of any impurity states between the band edges. Additionally, the absorption edge of the solar spectrum shifts toward lower photon energy from 3.5 to 3.1 eV. From Bader charge analysis, we observed that mainly the charge transfer occurred from the dopants and charge accumulation happened around nearby oxygen atoms. The ferromagnetism was observed in V-, Cr-, Mo-, and W-doped anatase TiO2 structures due to the charge imbalance of the spin-up and spin-down states.