Spin-polarized Electronic Structure Research Articles

Magnetism in two dimensional CoX$_2$ (X=S, Se, Te), from monolayer to bulk layered structures

We investigate spin-polarized electronic structures of CoX$_2$ (X=S, Se, Te) monolayers using the density functional theory. We find that CoS$_2$ and CoSe$_2$ monolayers are metallic ferromagnetic materials, whereas CoTe$_2$ monolayer is non-magnetic metallic material. The 3D bulk layered crystalline structures of CoX$_2$ (X=S, Se, Te) are found to be non-magnetic metals in our calculations. In addition to the major contributions due to the $d$ orbitals of Co atoms, there is also contribution from the $p$ orbitals of chalcogen X atoms to the magnetism in CoX$_2$. The crystal field spliting and distance between the neighbouring magnetic atoms play a significant role to induce magnetism in these structures. We are optimistic for the experimental growth and uses of these monolayer structures for the 2D spintronic applications.

Theoretical perspectives on the electronic, optical, mechanical, magnetic, and anisotropic behaviors of the quaternary Heusler alloys RhFeMnZ and IrMnCrZ (where Z = Si, Ge)

High-spin-polarised materials are the most promising candidates for spintronic devices. Here, the spin-polarised electronic structure, magnetism, mechanical, and optical properties of RhFeMnZ and IrMnCrZ (where Z = Si, Ge) Quaternary Heusler alloys were calculated by first-principles calculations. The calculations show that type III for the RhFeMnSi, RhFeMnGe, and IrMnCrSi and type I for the IrMnCrGe compound configuration is the most stable crystal structure for the studied alloys. The four alloys were found to have a half-metallic ferromagnetic structure with indirect band gaps in the majority spin channels of 0.957, 0.66, 0.745, and 0.891 eV for RhFeMnSi, RhFeMnGe, IrMnCrSi, and IrMnCrGe, respectively. They exhibit an appreciable total magnetic moment of 4 μB for RhFeMnZ (Z = Si, Ge) and 2 μB for IrMnCrZ (Z = Si, Ge). The results show that RhFeMnZ and IrMnCrZ (where Z = Si, Ge) are ferromagnetic half-metals with 100 % spin polarisation. The results of the elastic constants demonstrate the mechanical stability of RhFeMnZ and IrMnCrZ (where Z = Si, Ge) alloys. Optical properties such as dielectric function, absorption, reflectance, optical conductivity, and other optical properties were also probed. In the ultraviolet region, RhFeMnZ and IrMnCrZ (where Z = Si, Ge) are effective absorbers and have a high refractive index. Alloys are promising candidates for potential applications in spintronic devices.

Optimizing the thermoelectric behavior of novel quaternary CoIrMnX (X=Sn, Sb) alloys through chemical potential or carrier concentration doping

Materials exhibiting significant polarisation at high spin rates are considered the most promising candidates for spintronic devices. This study investigates the mechanical, optical, spin-polarised electronic structure, magnetism, and thermoelectric properties of CoIrMnX (where X = Sn, Sb). We performed calculations of quaternary Heusler alloys using first-principles calculations. The CoIrMnSn and CoIrMnSb compounds have the most stable Type III crystal structures, according to the calculations performed on the alloys under investigation. We found that the two alloys, CoIrMnSn and CoIrMnSb, possessed a half-metallic ferromagnetic structure, characterised by indirect band gaps of 1.008 eV and 0.806 eV in the predominant spin channels, respectively. Both alloys demonstrate a significant overall magnetic moment of 5 and 6 μβ, respectively. CoIrMnX (where X = Sn, Sb) are ferromagnetic half-metals with 100 percent spin polarisation, according to the results. The results of the elastic constants demonstrate the alloys' mechanical stability. We also investigated optical characteristics such as dielectric function, absorption, reflectance, and optical conductivity. CoIrMnX (where X = Sn and Sb) acts as an efficient absorber in the ultraviolet region and possesses a high refractive index. Alloys exhibit considerable potential as viable candidates for implementation in spintronic devices. The maximum ZT value for CoIrMnSn (CoIrMnSb) is 0.915 (0.6619). To achieve this value, it is necessary to either reduce the charge carrier concentration to n = 0.0812 x 1020 (0.0952 x 1020) cm-3 or the μ to 0.83843 (0.83806) Ryd. Substantially examined materials demonstrate considerable potential for application in the field of thermoelectrics.

First Principles Calculations of Novel Binary Transition Metal Oxides NaCr0.5X0.5O2 (X = Y, Tc, Rh) for Na-Ion Batteries

Recently, layered transition metal oxides have demonstrated voltage windows favorable for use as cathodes in sodium-ion batteries, leading to increased specific capacity and energy density. Here, NaCr0.5Y0.5O2, NaCr0.5Tc0.5O2, and NaCr0.5Rh0.5O2 were studied by using first-principles calculations to elucidate their properties. There is a trigonal arrangement in the structure of both pure and substituted NaCrO2. Structural characteristics reveal the ferromagnetic behavior of these compounds (NaCr0.5X0.5O2; X = Y, Tc, Rh). We calculated the density of states and spin-polarized electronic band structures for the three compounds tested. NaCr0.5Y0.5O2 and NaCr0.5Rh0.5O2 exhibit diluted magnetic semiconductor (DMS) behavior, while NaCr0.5Tc0.5O2 has half-metallic (HM) behavior. The substitutional material’s ferromagnetic nature is confirmed by the negative values of the exchange constants (Nօ α and Nօ β). The fractional value of the magnetic moment also confirms the DMS nature of NaCr0.5Y0.5O2 and NaCr0.5Rh0.5O2, while the HM behavior is confirmed by the integral value of the magnetic moment for NaCr0.5Tc0.5O2. The thermoelectric characteristics were computed using the BoltzTraP code. Alectrochemical analysis of NaCr0.5Y0.5O2 showed a theoretical discharge capacity of 400 mhAg−1 and an average intercalation voltage of 4.87 V, calculated from the total energies of the optimized compounds and their de-sodianted phases. These theoretical computations demonstrate that the binary layered TM oxides studied are appropriate substances to employ in coin cell fabrication as cathodes.

Origins of multi-sublattice magnetism and superexchange interactions in double–double perovskite CaMnCrSbO6

The multi-sublattice magnetism and electronic structure in double–double perovskite compound CaMnCrSbO6 is explored using density functional theory. The bulk magnetization and neutron diffraction suggest a ferrimagnetic order ( TC∼ 49 K) between between Mn2+ and Cr3+ spins. Due to the non-equivalent Mn atoms (labelled as Mn(1) and Mn(2) which have tetrahedral and planar oxygen coordinations, respectively) and the Cr atom in the centre of distorted oxygen octahedron in the unit cell, the exchange interactions are more complex than that expected from a two sublattice magnetic system. The separations between the on-site energies of the d-orbitals of Mn(1), Mn(2) and Cr obtained from Wannier function analysis are in agreement with their expected crystal field splitting. While the DOS obtained from non spin-polarized calculations show a metallic character, starting from Hubbard U = 0 eV the spin-polarized electronic structure calculations yield a ferrimagnetic insulating ground state. The band gap increases with Ueff (U − J), thereby showing a Mott–Hubbard nature of the system. The inclusion of anti-site disorder in the calculations show decrease in band-gap and also reduction in the total magnetic moment. Due to the ∼90∘ superexchange, nearest neighbour exchange constants obtained from DFT are an order of magnitude smaller than those reported for various magnetic perovskite and double-perovskite compounds. The Mn(1)–O–Mn(2) (out of plane and in-plane), Mn(1)–O–Cr and Mn(2)–O–Cr superexchange interactions are found to be anti-ferromagnetic, while the Cr–O–O–Cr super-superexchange is found to be ferromagnetic. The Mn(2)–O–Cr superexchange is weaker than the Mn(1)–O–Cr super-exchange, thus effectively resulting in ferrimagnetism. From a simple 3-site Hubbard model, we derived expressions for the antiferromagnetic superexchange strength JAFM and also for the weaker ferromagnetic JFM . The relative strengths of JAFM for the various superexchange interactions are in agreement with those obtained from DFT. The expression for Cr–O–O–Cr super-superexchange strength ( J~SS ), which has been derived considering a 4-site Hubbard model, predicts a ferromagnetic exchange in agreement with DFT. Finally, our mean field calculations reveal that assuming a set of four magnetic sub-lattices for Mn2+ spins and a single magnetic sublattice for Cr3+ spins yields a much improved T C , while a simple two magnetic sublattice model yields a much higher T C .

Manipulation of energy-resolved magneto–optical effect in yttrium iron garnet films achieved by covering with nonmagnetic metals

The effect of the interface-driven magnetic optical (MO) manipulation on Pt/Yttrium iron garnet (YIG) and Cu/YIG has been investigated using energy-resolved magnetic circular dichroism (ER-MCD) system. By mapping the spatial MCD at different excitation energies, the results indicate manipulation of the spin-polarized electronic structure of YIG through interface charge transfer. Specifically, compared to the Cu/YIG region, we found that the Pt/YIG region exhibited a higher level of MCD enhancement and even a pronounced MCD sign inversion at certain excitation energies. In contrast, the saturation moment of the Pt-covered YIG film decreased significantly, while the enhancement was only slight for the Cu-covered YIG film. Based on the first-principles calculations, the presence of distinct polarized interface states of tetrahedral Fe ions in metal/YIG systems results in conflicting observations regarding optical and magnetic proximity effects. We present evidence that ER-MCD can effectively reveal dominant spin-polarized optical transitions in ferrimagnetic (FIM) materials, providing direct access to the polarized interface states in the nonmagnetic metal (NM)/FIM heterosystem. This capability opens opportunities to manipulate and customize the magneto–optical effect with energy resolution for various applications in magneto-optics.

Intrinsic Room-Temperature Ferromagnetism in New Halide Perovskite AgCrX3 (X: F, Cl, Br, I) Using Ab Initio and Monte Carlo Simulations.

Herein, we present a detailed comparative study of the structural, elastic, electronic, and magnetic properties of a series of new halide perovskite AgCrX3 (X: F, Cl, Br, I) crystal structures using density functional theory, mean-field theory (MFT), and quantum Monte Carlo (MC) simulations. As demonstrated by the negative formation energy and Born-Huang stability criteria, the suggested perovskite compounds show potential stability in the cubic crystal structure. The materials are ductile because the Pugh's ratio is greater than 1.75, and the Cauchy pressure (C12-C44) is positive. The ground state magnetic moments of the compound were calculated as 3.70, 3.91, 3.92, and 3.91 μB for AgCrF3, AgCrCl3, AgCrBr3, and AgCrI3, respectively. The GGA + SOC computed spin-polarized electronic structures reveal ferromagnetism and confirm the metallic character in all of these compounds under consideration. These characteristics are robust under a ±3% strained lattice constant. Using relativistic pseudopotentials, the total energy is calculated, which yields that the single ion anisotropy is 0.004 meV and the z-axis is the hard-axis in the series of AgCrX3 (X: F, Cl, Br, and I) compounds. Further, to explore room-temperature intrinsic ferromagnetism, we considered ferromagnetic and antiferromagnetic interactions of the magnetic ions in the compounds by considering a supercell with 2 × 2 × 2 dimensions. The transition temperature is estimated by two models, namely, MFT and MC simulations. The calculated Curie temperatures using MC simulations are 518.35, 624.30, 517.94, and 497.28 K, with ±5% error for AgCrF3, AgCrCl3, AgCrBr3, and AgCrI3 compounds, respectively. Our results suggest that halide perovskite AgCrX3 compounds are promising materials for spintronic nanodevices at room temperature and provide new recommendations. For the first time, we report results for novel halide perovskite compounds based on Ag and Cr atoms.

Iron-arsenide monolayers as an anode material for lithium-ion batteries: a first-principles study.

This theoretical investigation delves into the structural, electronic, and electrochemical properties of two hexagonal iron-arsenide monolayers, 1T-FeAs and 1H-FeAs, focusing on their potential as anode materials for lithium-ion batteries. Previous studies have highlighted the ferromagnetic nature of 1T-FeAs at room temperature. Our calculations reveal that both phases exhibit metallic behaviour with spin-polarized electronic band structures. Electrochemical studies show that the 1T-FeAs monolayer has better ionic conductivity for Li ions than the 1H-FeAs phase, attributed to a lower activation barrier of 0.38 eV. This characteristic suggests a faster charge/discharge rate. Both FeAs phases exhibit comparable theoretical capacities (374 mA h g-1), outperforming commercial graphite anodes. The average open-circuit voltage for maximum Li atom adsorption is 0.61 V for 1H-FeAs and 0.44 V for 1T-FeAs. The volume expansion over the maximum adsorption of Li atoms on both phases is also remarkably less than the commercially used anode material such as graphite. Furthermore, the adsorption of Li atoms onto 1H-FeAs induces a remarkable transition from ferromagnetism to anti-ferromagnetism, with minimal impact on the electronic band structure. In contrast, the original state of 1T-FeAs remains unaffected by Li adsorption. To summarize, both 1T-FeAs and 1H-FeAs monolayers have potential as promising anode materials for lithium-ion batteries, offering valuable insights into their electrochemical performance and phase transition behaviour upon Li adsorption.

Theoretical study of adsorption properties and electrical transport performance of toxic gas molecules on novel orthorhombic BN monolayer semiconductor

The adsorption properties of toxic gases on the surface of low-dimensional nanomaterials are a research hot topic and key issue for developing semiconductor sensors to detect toxic gas molecules. Recently, a novel orthorhombic BN monolayer has attracted extensive attention from researchers. Using first principles calculations, we investigate the adsorption properties of typical toxic gas molecules, such as CO, H<sub>2</sub>S, NH<sub>3</sub>, NO, NO<sub>2</sub>, and SO<sub>2</sub> molecules, on the surface of two-dimensional (2D) orthorhombic BN monolayer adsorption. The calculated adsorption energy show that the adsorptions of the above six molecules on the surface of BN monolayer are energy-favorable exothermic processes. It is found that NO<sub>2</sub> and NH<sub>3</sub> molecules are of chemical adsorption, while other systems are of physical adsorption, and NO adsorbing system exhibits a spin-polarized electronic band structure. The calculated density of states reveals that the adsorption of NO molecule and SO<sub>2</sub> molecule have significant influences on the electronic structure near the Fermi level. Moreover, the adsorption of the NO<sub>2</sub> molecule on the substrate exhibits remarkable variation of the work function, suggesting that the o-BN monolayer possesses excellent selectivity and sensitivity to NO<sub>2</sub> molecule. In addition, we use first principles combined with non-equilibrium Green’s function to simulate the electrical transport properties of monolayered o-BN semiconductor based nanodevice with adsorption of typical toxic gas molecules. The <i>I-V</i><sub>b</sub> curve shows that the current through the nanodevice is 6500 nA for the NO<sub>2</sub> molecule adsorbing system under 1 V bias voltage. The calculation results reveal that the adsorption of NO<sub>2</sub> molecule on the o-BN monolayer can significantly enhance its electrical transport performance, and the o-BN monolayer possesses excellent sensitivity and selectivity to the NO<sub>2</sub> gas molecule. The work function and the charge transfer can be effectively manipulated by tensile strain, indicating its potential application in anisotropic electronics. Our results indicate that the o-BN monolayer has excellent adsorption performance to toxic gases, showing its practical application in capturing toxic gas molecules as a gas sensor in future.

Modeling and tuning the electronic, mechanical and optical properties of a recently synthesized 2D polyaramid: a first principles study.

This work delves into a methodology of modeling 2D materials and their structural engineering, considering an example of a recently synthesized 2D polyaramid (2DPA-1). A bottom-up approach similar to experimental techniques is implemented for modeling, and then its electronic structures and phonon spectrum and the quadratic nature of flexural phonons are analyzed. Furthermore, boron and nitrogen atoms are substituted for the carbon atom of the amide group of 2DPA-1, and their effects on its electronic properties, phonon spectrum, and mechanical properties are compared with those of pristine 2DPA-1 using density functional theory calculations. The ab initio molecular dynamics (AIMD) simulations validate the thermal stability of our system at high temperatures. The spin-polarized electronic structures reveal the transformation of pristine 2DPA-1 from a semiconductor to a half-metal and its magnetic behaviour upon nitrogen substitution. Constraining the quadratic nature of flexural phonons using the Born-Huang criteria significantly enhances the phonon spectra, leading to more accurate and reliable simulations. For modulated 2DPA-1, the elastic modulus varies between 17 and 27 N m-1, and the absorption peaks shift from ∼5.15 eV to 2.42 eV, enabling the application of polymeric 2D nanomaterials in photocatalysis and sensing, where light absorption in the near-infrared region is important. Finally, validation of our methodology is confirmed, as computed Young's modulus (11.26-11.76 GPa) of 2DPA-1 matches excellently with the experimental value (12.7 ± 3.8 GPa). Overall, this study reveals the modeling of a newly synthesized polymeric 2D material, and tuning its properties results in smaller bandgaps and half-metallic and magnetic behaviours.

Theoretical Study on the Open-Shell Electronic Structure and Electron Conductivity of [18]Annulene as a Molecular Parallel Circuit Model.

Herein, the electron conductivities of [18]annulene and its derivatives are theoretically examined as a molecular parallel circuit model consisting of two linear polyenes. Their electron conductivities are estimated by elastic scattering Green's function (ESGF) theory and density functional theory (DFT) methods. The calculated conductivity of the [18]annulene does not follow the classical conductivity, i.e., Ohm's law, suggesting the importance of a quantum interference effect in single molecules. By introducing electron-withdrawing groups into the annulene framework, on the other hand, a spin-polarized electronic structure appears, and the quantum interference effect is significantly suppressed. In addition, the total current is affected by the spin polarization because of the asymmetry in the coupling constant between the molecule and electrodes. From these results, it is suggested that the electron conductivity as well as the quantum interference effect of π-conjugated molecular systems can be designed using their open-shell nature, which is chemically controlled by the substituents.

Electronic properties of SiC nanoribbon

The electronic properties of zigzag and armchair SiC nanoribbons are studied using a theoretical method. The spin-unrestricted electronic behavior of an armchair and zigzag SiC nanoribbon containing Si and C vacancy in the supercell was investigated. Spin-polarized electronic structure calculations show that armchair SiC nanoribbon was classified as a nonmagnetic semiconductor while zigzag SiC nanoribbon presents a half-metallic electronic structure. Our results suggest that SiC nanoribbon containing point vacancy may be a good candidate for spintronics due to its half-metal properties.

First-principles calculations to investigate Structural, mechanical, electronic, magnetic and thermoelectric properties of MRh2O4 (M = Mg, Mn, Cd) spinel oxides

Structural, mechanical, magnetic, electronic and thermoelectric properties of MRh2O4 (M = Mg, Mn, Cd) spinel oxides are studied through first-principles calculations. Calculations of structural and elastic stiffness constants (Cij’s) show that the MRh2O4 oxides are stable structurally and mechanically. Elastomechanical results show that the CdRh2O4 is ductile, MnRh2O4 is brittle, while MgRh2O4 lies on the borderline differentiating the ductile and brittle character. MnRh2O4 has high bulk modulus and high Young’s modulus which indicate its ability to resist plastic deformation. MnRh2O4 spinel oxide bears the highest values of Debye temperature (TD = 634.4 K) and melting temperature (Tm = 3530.4 K) among the MRh2O4 (M = Mg, Mn, Cd) oxides. Band structure calculations and density of states spectra indicate the p-type semiconducting nature of MRh2O4 (M = Mg, Mn, Cd) oxides. Spin-polarized electronic structure of CdRh2O4 show 100 % spin-polarized behavior, while MgRh2O4 and MnRh2O4 oxides show 0.12 % and 0.29 % spin-polarization, respectively. MnRh2O4 exhibits saturation magnetization Ms = 172 emu/g and total magnetic moment mtot = 9.99 µB/f.u. Temperature dependent thermoelectric properties (thermal conductivity, electrical conductivity, Seebeck coefficient, Hall coefficient, power factor and figure of merit) are also studied for MRh2O4 oxides. Calculated thermoelectric properties of MRh2O4 (M = Mg, Mn, Cd) oxides show that these oxides are promising for applications as novel thermoelectric materials.

Physical properties of W2GaX (X=C, N, and F) based novel MAX phases; potential materials for applications in advanced electronic and optical devices

This study examines the electronic and optical characteristics of W2GaX (X = C, N, and F) MAX phases using first-principles approach. The cohesive energies of W2GaC, W2GaN, and W2GaF are determined as 7.31, 6.40, and 5.05 eV, respectively, demonstrating excellent agreement with existing literature and confirming their stability. The W-d, Ga-s, and X-p states are symmetrically dispersed across the spin-polarized electronic structures, resulting in a nonmagnetic metallic behavior of W2GaX. Due to their metallic behavior, they reflect more than 60 % of infrared and up to 50 % of visible light. These compounds demonstrate considerable absorption of infrared, visible, and ultraviolet (UV) light, with absorption coefficients of approximately ∼104 cm−1, ∼105 cm−1, and ∼106 cm−1, respectively. The refractive indices of W2GaX MAX phases remain greater than one for incident light energies below 10 eV. Additionally, W2GaC shows the highest optical conductivity among the investigated compounds when exposed to light, making it a promising material for various conduction applications. Our present study sheds light on the optical and electronic properties of W2GaX MAX phases and highlights their potential for applications in advanced electronic and optical devices.

Excitonic effects on the optical spectra of TiB2 nanosheets

Two-dimensional (2D) transition metal borides, have recently attracted tremendous interest and become an emerging class of 2D materials due to their intriguing properties. We report systematic investigation of stability, electronic properties and optical activity of 2D-TiB2 nanosheets using first-principles calculations. By combining elastic and phonon-dispersion calculations, we substantiated the mechanical and dynamic stability of 2D-TiB2 nanosheets. Our results of elastic calculations reveal that addition of an extra layer destroys the auxetic behaviour of monolayer (ML) 2D-TiB2 with significant reduction in the brittleness. Further, based on the spin-polarised electronic structure calculations, we find that a low-dimensional metallic state of ML can be achieved by tuning the distance between the titanium and boron layers. The calculations clearly reveal that metallic nature does not destroys the auxetic behaviour of ML. Subsequently, we investigated the optical response of 2D-TiB2 nanosheets (ML and bilayer (BL)) at the level of density functional theory and many-body perturbation theory. The results obtained by solving Bethe–Salpeter equation (GW+BSE formalism) shows that excitonic effects causes a slight blue-shift in the absorption spectra of the nanosheets with ML being optically active with sharp peaks in infrared (IR) and ultraviolet (UV) regions while BL shows the reduced optical activity across wide range of photon energies spanning the near-IR to UV region. In addition, electronic polarisability of the nanosheet decreases with addition of another layer in ML 2D-TiB2. Further investigation of transition probabilities clearly indicates that the response of ML at Dirac point is tunable by spin–orbital coupling effects which makes these nanosheets promising for spintronic applications. The BL exhibits distinct electronic, and optical properties compared to ML. Our study unravels the structural, elastic, electronic, and optical properties of 2D-TiB2 nanosheets and suggests them as promising candidate for variety of optoelectronic and spintronic applications.

Cation exchange route to a Eu(II)-containing tantalum oxide

Traditional synthetic efforts to prepare Eu(II)-containing oxides have principally involved the use of high temperature reactions starting from EuO or a controlled, highly-reducing, atmosphere. Conversely, chimie douce approaches that are more amenable to the targeted syntheses of new, and potentially metastable, Eu(II)-oxides have yet to be explored. Herein, a cation-exchange route to new Eu(II)-containing oxides, e.g., EuTa4-xO11 (x = 0.04), has been discovered and its structure determined by powder X-ray diffraction (Space group P6322 (#182), a = 6.2539(2) Å; c = 12.3417(2) Å). The compound derives from the cation exchange of Na2Ta4O11, via a reaction with EuBr2 at 1173 K, and replacement by half the number of divalent Eu cations. Rietveld refinements show preferential ordering of the Eu cations over one of the two possible cation sites, i.e., Wyckoff site 2d (∼94%; Eu1) versus 2b (∼6%; Eu2). Total energy calculations confirm an energetic preference of the Eu cation in the 2d site. Tantalum vacancies of ∼1% occur within the layer of Eu cations and TaO6 octahedra, and ∼20% partial oxidation of Eu(II) to Eu(III) cations from charge balance considerations. 151Eu Mössbauer spectroscopy measured at 78 K found a Eu(II):Eu(III) ratio of 69:31, with a relatively broad line width of the former signal of Γ = 7.6(2) mm s–1. Also, the temperature-dependent magnetic susceptibility could be fitted to a Curie Weiss expression, giving a μeff = 6.2 μB and θCW = −10 K and confirming a mixture of Eu(II)/Eu(III) cations. The optical bandgap of EuTa4-xO11 was found to be ∼1.5 eV (indirect), significantly redshifted as compared to ∼4.1 eV for Na2Ta4O11. Spin-polarized electronic structure calculations show that this redshift stems from the addition of Eu 4f7 states as a higher-energy valence band. Thus, these results demonstrate a new cation-exchange approach that represents a useful synthetic pathway to new Eu(II)-containing oxides for tunable magnetic and optical properties.

Robust half-metallic ferromagnet in doped double perovskite Sr2TiCoO6 by rare-earth elements for photovoltaic and thermoelectric conversion: A DFT method

In this study, we have discovered a novel candidate series of half-metals by replacement of the Ti atom with the rare-earth elements RE (=Dy, Ho, Er, or Tm) in the double perovskite Sr2TiCoO6. We methodically investigated the electronic, magneto-optical, and thermoelectric characteristics of the compounds Sr2(RE)CoO6 using the FP-LAPW method. The spin-polarized electronic structure studied within GGA-WC and GGA + U showed a robust half-metallic character for all compounds. The substitution by the rare-earth elements RE enhanced the magnetic characteristics of Sr2TiCoO6, which exhibits a transition from a total magnetic moment of 1μB for Sr2TiCoO6 to 7μB, 6μB, 5μB, and 4μB for Sr2DyCoO6, Sr2HoCoO6, Sr2ErCoO6, and Sr2TmCoO6, respectively. However, the hybridization between RE-4f, Co-3d, and O-2p is responsible for robust half-metallic ferromagnet in Sr2(RE)CoO6 compounds. We have also studied the effect of spin-orbit coupling (SOC) on electronic structure. The Sr2DyCoO6, Sr2HoCoO6, and Sr2ErCoO6 compounds maintained their half-metallicity under GGA + SOC, whereas Sr2TmCoO6 became a magnetic metal. An in-depth analysis of the optical and thermoelectric characteristics was performed by GGA + U. According to the absorption coefficient and imaginary part of the dielectric function, we have found that the compounds Sr2(RE)CoO6 have better absorption quantities at different frequencies (IR, visible, and UV) than Sr2TiCoO6. Due to their high ZT and good Seebeck coefficient in a spin-up canal, the investigated compounds have excellent thermoelectric efficiency. These characteristics make the double perovskites Sr2(RE)CoO6 as a high absorber an attractive choice for photovoltaic solar cells and thermoelectric applications.

The influence of pressure on the spin-polarized electronic structure of ZnSeTe:T (Т=Cr, Mn, Fe) doped solid solution

The electronic and magnetic properties of the solid solutions of ZnSeTe, in which the Zn atom is replaced by the transition 3d element Cr, Mn, or Fe, were calculated for 64-atom supercells. The shift of the Fermi level toward the valence band states due to pressure was revealed. It was established that at pressures p = 0 and p = 33 GPa, for both spin orientations, the ZnCrSeTe material is a semimetal, and the ZnMnSeTe material is a semiconductor. However, the ZnFeSeTe material is a semimetal at a pressure of p = 0 and a non-magnetic metal at a pressure of p = 33 GPa.

Optical and magnetic characteristics of BaTi1-xCoxO3: A first-principles study

The full potential linearized augmented plane wave (FP-LAPW) approach based on the density functional theory (DFT) is employed to know the effect of Co doping on the electronic, optical, and magnetic characteristics of BaTi1-xCoxO3 at x= 8.33%, 16.66%, 25%, and 50%. The computed spin-polarized electronic band structure (BS) and the density of states (DOS) elucidate that the BaTi1-xCoxO3 compound has a ferromagnetic semiconductor behavior at all doping concentrations. The results indicate that the magnetic moment in BaTi1-xCoxO3 is found due to the p-d hybrid orbitals of Co. Moreover, the optical features of the Co-doped BTO compound are evaluated by analyzing the refractive index, reflectivity, absorption coefficient, optical conductivity, and dielectric constant under different concentrations. The outcomes revealed that the BaTi1-xCoxO3 compound is a good candidate for spintronics and optoelectronic applications.

Half-metallicity feature within Ag-doped zincblende WGe alloys: DFT+U insights

By employing the full-potential linearized augmented plane wave (FP-L/APW[Formula: see text]lo) technique based on density functional theory (DFT), the structural, electronic and magnetic properties of zincblende W[Formula: see text]AgxGe alloys ([Formula: see text] and 0.25) are scrutinized thoroughly. Based on the generalized gradient approximation (GGA), the exchange-correlation energy functional is included in the current simulation. For computing the structural features, the GGA approximation is applied, whereas GGA, [Formula: see text] and the modified Burke–Johnson of [Formula: see text] (TB-mBJ-[Formula: see text] approximations are incorporated to perform the calculations of electronic and magnetic behaviors of these alloys. The structural analysis of the alloys indicated that the total energy of the W[Formula: see text]Ag[Formula: see text]Ge alloy was favorable in the ferromagnetic ground state. The spin-polarized electronic structure shows the half-metallic behavior of the W[Formula: see text]Ag[Formula: see text]Ge alloy, while the WGe compound is identified as a metal. The magnetic results obtained from the half-metallic W[Formula: see text]Ag[Formula: see text]Ge alloy increasingly support the full half-metallicity of this compound because an integer value is acquired for the total magnetic moment. The strong hybridization between 4p-Ge and 3d-W states brings forth weak local magnetic moments at the nonmagnetic Ge atomic sites and reduces the local magnetic moment of the W atomic sites from its free space charge.