Spin-dependent Band Structure Research Articles

Thermodynamical stability and optoelectronic characteristics of Sr1-xCoxTe: A DFT study

Herein, the structural, electronic, magnetic and optical features of Sr1-xCoxTe alloys are investigated by using first-principles calculations. Stability of alloys is confirmed by the enthalpy of formation energy. The spin-dependent band structure (BS) and density of states (DOS) elucidate the half-metallic ferromagnetic (HMF) nature. For spin-down channel, Sr1-xCoxTe (x = 6.25 %, 12.5 %, 25 %) alloys have bandgap values of 1.30, 0.79 and 0.41 eV, respectively. The computed total magnetic moment for Sr1-xCoxTe (x = 6.25 %, 12.5 %, 25 %) are 3.00003, 5.99801, and 10.01265 μB, respectively. This robust magnetic ordering is primarily originated due to the incorporation of Co cations, which is further confirmed by spin magnetic density visualizer plots. Moreover, the optical features including dielectric constants, absorption, refraction and reflectivity of studied alloys have been analyzed within energy range 0–10 eV. Upon Co incorporation, the resulting alloys become optically active in the visible region of light. Overall, presented results suggest that Co-doped SrTe could be a potential material for optoelectronic and spintronic applications.

Spin-Charge Conversion in Chiral Polymers with Hopping Conduction.

Organic and biological materials are often chiral. Chiral polymers, as recent experiments indicate, facilitate spin-charge conversion: a charge current results in a spin polarization and vice versa, dubbed chirality-induced spin selectivity (CISS) and inverse CISS (ICISS). While CISS/ICISS in crystalline chiral systems such as tellurium can be understood in terms of their chirality- and spin-dependent band structure, such a picture becomes inapplicable to disordered chiral polymers, where carrier transport is via hopping rather than band conduction. Here, we develop a microscopic theory to describe CISS and ICISS in disordered chiral organics, in which chirality-induced geometric spin-orbit coupling leads to a purely geometric spin-dependent Berry phase in electron hops involving triads, whose orientations are dictated by the material's chirality. Our theory reveals a central role of spin-flip hopping, which suppresses CISS but enables ICISS.

Predicting Spin-Dependent Phonon Band Structures of HKUST-1 Using Density Functional Theory and Machine-Learned Interatomic Potentials.

The present study focuses on the spin-dependent vibrational properties of HKUST-1, a metal-organic framework with potential applications in gas storage and separation. Employing density functional theory (DFT), we explore the consequences of spin couplings in the copper paddle wheels (as the secondary building units of HKUST-1) on the material's vibrational properties. By systematically screening the impact of the spin state on the phonon bands and densities of states in the various frequency regions, we identify asymmetric -COO- stretching vibrations as being most affected by different types of magnetic couplings. Notably, we also show that the DFT-derived insights can be quantitatively reproduced employing suitably parametrized, state-of-the-art machine-learned classical potentials with root-mean-square deviations from the DFT results between 3 cm-1 and 7 cm-1. This demonstrates the potential of machine-learned classical force fields for predicting the spin-dependent properties of complex materials, even when explicitly considering spins only for the generation of the reference data used in the force-field parametrization process.

Excellent spin diode and spin-dependent Seebeck effects in hetero-junctions based on ferromagnetic Cr3M4 (M = Se, Te)

Ferromagnetic (FM) half-metals have been regarded as the most promising candidates for spin injection into semiconductors due to their completely spin-polarized electronic states around the Fermi level. To explore the potential application of Cr3M4 (M = Se, Te) in spintronic devices, which are experimentally synthesized FM bulks as well as half-metallic monolayers with high Curie temperature, we propose to design a Bi2Se3/Cr3Se4 van der Waals hetero-junction and a 2D Cr3S4/Cr3Te4 hetero-junction motivated by the recent report on controlling synthesis of Cr x M y based heterostructures. First-principles calculations combined with non-equilibrium Green’s function uncover the perfect spin filtering and spin diode effect in Bi2Se3/Cr3Se4 van der Waals hetero-junction. More interestingly, the Cr3S4/Cr3Te4 hetero-junction shows an excellent spin-dependent Seebeck effect, in which spin-dependent currents with opposite spin orientation can be driven by a temperature gradient to flow in the opposite transport direction. These effects can be understood from the calculated spin-dependent band structures and transmission spectrum. Our results put forward a promising designing and application of spintronic devices based on Cr3M4 (M = Se, Te) FM materials.

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.

Magnetic, optoelectronic, and thermoelectric characteristics of Ln2MnSe4 (Ln = Yb, Lu) spinel chalcogenides: A DFT investigation

Herein, structural, optical, magnetic, electronic, and thermoelectric (TE) characteristics of cubic spinels Ln2MnSe4 (Ln = Yb, Lu) are examined by DFT + U. Enthalpy of formation (ΔHf) for both spinels are negative (−3.189 and −2.251 eV for Yb2MnSe4 and Lu2MnSe4, correspondingly), which supports thermodynamical stability for both spinels. Spin dependent band structures and density of state (DOS) disclose the half metallic and magnetic semiconducting nature for both Ln2MnSe4 (Ln = Yb, Lu) spinels, respectively, with direct bandgaps of 1.44 eV in spin up and metallic in spin down for Yb2MnSe4 whereas Lu2MnSe4 has 0.5/1.5 eV in spin up/down channel. Optical response of Ln2MnSe4 (Ln = Yb, Lu) spinels is also determined. At 0 eV, the computed results of refractive index n (ω) for Yb2MnSe4/Lu2MnSe4 are 12.0/2.89, respectively. For Yb2MnSe4 and Lu2MnSe4 peak value of σ(ω) are calculated as 7813.08 at 7.03 eV and 7532.71 (1/Ωcm) at 6.47 eV, respectively. To assess the temperature dependent transport behavior of both compounds, thermoelectric (TE) characteristics including power factor (PF), Seebeck coefficient (S), thermal conductivity (k/τ), electrical conductivity (σ/τ) and figure of merit (ZT) are determined. Maximum ZT values for Yb2MnSe4 and Lu2MnSe4 are 0.18 and 0.79 at 800 K, correspondingly. Results show that Yb2MnSe4 is suitable contender spintronics due to 100% spin polarization at Fermi level whereas Lu2MnSe4 is useful addition to magnetic semiconductor family having potential applications in opto-electronic and TE devices.

Mn-X (X = F, Cl, Br, I) Co-Doped GeSe Monolayers: Stabilities and Electronic, Spintronic and Optical Properties.

GeSe monolayer (ML) has recently attracted much interest due to its unique structure and excellent physical properties that can be effectively tuned through single doping of various elements. However, the co-doping effects on GeSe ML are rarely studied. In this study, the structures and physical properties of Mn-X (X = F, Cl, Br, I) co-doped GeSe MLs are investigated by using first-principle calculations. The formation energy and phonon disspersion analyses reveal the stability of Mn-Cl and Mn-Br co-doped GeSe MLs and instability of Mn-F and Mn-I co-doped GeSe MLs. The stable Mn-X (X = Cl, Br) co-doped GeSe MLs exhibit complex bonding structures with respect to Mn-doped GeSe ML. More importantly, Mn-Cl and Mn-Br co-doping can not only tune magnetic properties, but also change the electronic properties of GeSe MLs, which makes Mn-X co-doped GeSe MLs indirect band semiconductors with anisotropic large carrier mobility and asymmetric spin-dependent band structures. Furthermore, Mn-X (X = Cl, Br) co-doped GeSe MLs show weakened in-plane optical absorption and reflection in the visible band. Our results may be useful for electronic, spintronic and optical applications based on Mn-X co-doped GeSe MLs.

Superior spin transport properties based on VS2 and VCl2 ferromagnetic monolayers

Two-dimensional ferromagnetic monolayers have attracted growing interest due to their promising applications in spintronic devices. To explore the potential application of monolayer VS2 and VCl2 in spintronic devices, previously reported ferromagnetic semiconductor and half-metal, respectively, we investigate the spin transport properties of VS2 homo-junction, VCl2 homo-junction, and lateral VS2–VCl2 heterostructure using first-principles combined with non-equilibrium Green's function. We show that monolayer VS2 exhibit superior spin Seebeck effect along an armchair direction, monolayer VCl2 is an excellent platform to realize a spin valve, and the magnetoresistance ratio is up to 1.3 × 104. Moreover, the VS2–VCl2 heterostructure exhibits an excellent spin diode effect. We explain these effects from the calculated spin-dependent band structure and transmission spectrum. The superior spin transport properties make monolayer VS2 and VCl2 promising candidates for spintronic applications.

Proximity-induced diversified magnetic states and electrically controllable spin polarization in bilayer graphene: Towards layered spintronics

Compared to monolayer graphene, electrons in Bernal-stacked bilayer graphene (BLG) have an additional layer degree of freedom, offering a platform for developing layered spintronics with the help of proximity-induced magnetism. Based on an effective phenomenological model, we systematically study the effect of this magnetism on the spin-dependent band structure near the Fermi energy and identify the magnetic phases induced in BLG by proximity with magnets. We show that spin polarization can develop in BLG due to this proximity effect. This spin polarization depends strongly on the layer distribution of magnetism, and can always be controlled by gate voltage which shifts spin-dependent band edges and modifies the total band gap. We further show that the band spin polarization can be modified by the proximity-induced staggered sublattice potential. By taking full advantage of layer-dependent magnetism in BLG, we propose that spintronic devices such as a spin filter, a giant magnetoresistance device, and a spin diode can operate under fully electric control, which is easier than the common magnetic field control.

Anomalously large spin-dependent electron correlation in the nearly half-metallic ferromagnet CoS2

The spin-dependent band structure of ${\mathrm{CoS}}_{2}$, which is a candidate for a half-metallic ferromagnet, was investigated by both spin- and angle-resolved photoemission spectroscopy and theoretical calculations to reappraise the half-metallicity and electronic correlations. We determined the three-dimensional Fermi surface and the spin-dependent band structure. As a result, we found that a part of the minority spin bands is on the occupied side in the vicinity of the Fermi level, providing spectroscopic evidence that ${\mathrm{CoS}}_{2}$ is not a half-metal but very close. Band calculations using density functional theory with generalized gradient approximation showed good agreement with the observed majority spin ${e}_{g}$ bands, while it could not explain the observed band width of the minority-spin ${e}_{g}$ bands. On the other hand, theoretical calculations using dynamical mean field theory could better reproduce the strong mass renormalization in the minority-spin ${e}_{g}$ bands. Our results strongly suggest the presence of anomalously enhanced spin-dependent electron correlation effects on the electronic structure in the vicinity of the half-metallic state. We also report the temperature dependence of the electronic structure across the Curie temperature and discuss the mechanism of the thermal demagnetization. Our discovery of the anomalously large spin-dependent electronic correlations not only demonstrates a key factor in understanding the electronic structure of half-metals but also provides a motivation to improve theoretical calculations on spin-polarized strongly correlated systems.

Giant nonlinear anomalous Hall effect induced by spin-dependent band structure evolution

The anomalous Hall effect (AHE) is a key transport signature revealing the topological properties of magnetic compounds. In quantum materials, the classical linear dependence of the AHE on magnetization often breaks down, which is typically ascribed to the presence of topological magnetic or electronic textures. However, the complex electronic structure of these compounds may offer alternative, unexplored mechanisms. Here, we show that a giant nonlinear AHE can originate from a series of magnetic-field-induced Lifshitz transitions in the spin-dependent band structure. In our experiments on ${\mathrm{EuCd}}_{2}{\mathrm{As}}_{2}$ the AHE contributes to 97% of the total Hall response, corresponding to a record anomalous Hall angle of 21%. Our scaling analysis and first-principles calculations demonstrate that the electronic structure is extremely sensitive to spin canting, with the magnetic field causing band crossing and band inversion and introducing a band gap when oriented along specific directions. Our results not only provide an ideal platform for Berry curvature engineering but reveal a general effect that may be applied to other material systems.

First-principles calculations to investigate structural, magnetic, optical, electronic and thermoelectric properties of X2MgS4(X=Gd, Tm) spinel sulfides

Full potential linearized augmented plan wave (FP-LAPW) method based on density functional theory (DFT) is used to explore the optoelectronic, structural, thermo-electric and magnetic characteristics of cubic X2MgS4 (X = Gd, Tm) spinel sulfides. Stability of ferromagnetic (FM) state is confirmed by optimizing the unit cells and the stability of the compound is confirmed by negative values (−8.381 eV for Gd2MgS4 and -7.448 eVfor Tm2MgS4) of formation enthalpy (Δ Hf). Spin dependent band structures (BS) and density of states (DOS) show that Tm2MgS4 is the half-metallic (HM) whereas Gd2MgS4 is semiconductor and has a band-gap (Eg) of 1.67 eV in spin up and 1.34 eV in spin down state. Computed magnetic-moments (μB) of cubic Gd2MgS4 and Tm2MgS4 are 28.000 μB and 8.003 μB, correspondingly, which is further confirmed by spin-polarized density. From thermoelectric (TE) features, Tm2MgS4 has maximum value of figure of merit (ZT) 0.782 and Gd2MgS4 has peak value 0.753 at 800 K and seebeck coefficient (S) shows maximum value of 242 μV/k for Gd2MgS4 and 254 μV/k for Tm2MgS4 at 750 K, which makes Tm2MgS4 more efficient material than Gd2MgS4. Moreover, optical parameters such as absorption coefficient α(ω), optical conductivity σ(ω), dielectric constant ε(ω), refractive index n(ω), reflectivity R(ω) and extinction coefficient k(ω) are also explored. Optical properties of the X2MgS4 (X = Gd, Tm) show that both materials are transparent in ultraviolet (UV) region, indicating that both are suitable for use in optical filters and sensors. According to findings studied compounds might be useful for spintronics, thermoelectric and optoelectronic applications.

Modeling and Simulation of High-Performance CrTe Intrinsic Half Metal-Based Spin Valve and Spin Diode

Most of the pristine two-dimensional materials such as graphene, silicene, germanene etc. are non-magnetic in nature and the creation of magnetism in these materials is subjected to the doping, external field, vacancy, strain etc., but their control in the experimental is very difficult. That has motivated the researchers for the exploration of 2D materials like Transition metal chalcogenides (TMC) with intrinsic magnetism. In the present study, the ferromagnetism of the two-dimensional Chromium telluride (CrTe) is verified by the spin-dependent density of states. Moreover, taking into consideration the similar crystal structure and comparable lattice constants of Vanadium telluride (VTe) to that of CrTe, we have modelled a three-layer spin valve (CrTe-VTe-CrTe) and a two-layer spin diode (CrTe-VTe), and simulated for spin-dependent transport characteristics. The performance parameters like spin injection efficiency, magnetoresistance, rectification ratio has been calculated to carry out the performance evaluation of the modelled devices. The spin valve displays 100% spin injection efficiency and large magnetoresistance of 3.46 × 108%, a comparative study has been carried out to evaluate the performance of the modelled spin valve. Moreover, the spin diode displays high spin filtering efficiency and good rectification ratio, which suggests the potential spintronic applications of the proposed devices. The spin-dependent transport characteristics have been justified by using spin-dependent transmission spectrum and spin-dependent band structure.

Investigation of the electronic and magnetic properties of low-dimensional FeCl2 derivatives by first-principles calculations

An FeCl2 monolayer is a half-metallic two-dimensional (2D) magnetic material, which has been investigated theoretically from different perspectives. In this paper, the electronic properties of the stable half-metallicity of a 2D trigonal FeCl2 nanosheets under external stress, magnetic modulation of electronic structures of quasi one-dimensional (1D) trigonal FeCl2 nanoribbons were calculated by the first-principle method. The calculated band structures show that the half-metallicity of a 2D trigonal FeCl2 nanosheet is dynamically stable and isotropic, and its half-metallicity is always presented in different structures as stress gradually increases along the armchair and zigzag directions. Meanwhile, the spin-dependent band structures of quasi-1D trigonal FeCl2 nanoribbons with diverse boundaries and distinct magnetic states show metallic, half-metallic or semiconductor characteristics. Most nanoribbons we considered were half-metallic in the ferromagnetic state, except for the nanoribbons with a width of 10 and both edges bounded by Cl atoms, which were metallic. Depending on nanoribbon width, the nanoribbons with Cl atoms on both edges showed semiconducting behavior along with oscillating band gaps in the nonmagnetic state, and metallic or half-metallic behavior in the antiferromagnetic state. The total energies revealed that the ferromagnetic state was the ground state of the FeCl2 nanoribbons with Cl on both edges. These extraordinary electronic structures indicate the promise of trigonal FeCl2 for use in spintronic devices.

Gold Nanosolenoids Based on Chiral Nanotubes Calculated Using the Relativistic Linearized Augmented Cylindrical Wave Method

Spin-dependent band structures, the electron and spin transport, and the formation of magnetic field in the single-walled chiral gold nanotubes (n1, n2) are calculated using a relativistic lineariz...

Magneto-electronic, mechanical, thermoelectric and thermodynamic properties of ductile perovskite Ba2SmNbO6

We have extensively explored crystal properties based on the structural optimization inclusive of elasto-mechanical, thermoelectric and thermodynamics of double layered perovskite Ba22+Sm3+Nb5+O62−. The generalised gradient approximation (GGA) within Perdew-Burke-Ernzerhof (PBE) functional along with Hubbard correction (U) were integrated to figure out exact electronic structure. Magnetic inetarctions suggest ferromagnetic phase as stable phase as also confirmed by thermodynamic calculations. Spin dependent band structures along with density of states envisages its perfect half-metallic character with a direct band gap of 3.32 eV under GGA + U approximation. The elastic properties has been evaluated to descript its mechanical strength, which convey its ductile nature. Boltzmann theory is employed to check the thermoelectric response, where Seebeck coefficient of 211.4 μVK−1 and power-factor of 1.12 × 1011 W/mK2s is seen. Furhter, the lattice thermal conductivity via Slack's equation is found to be 1.04 W/mK at room temperature which show a decaying trend towards high temperatures. The high temperature and pressure variation of thermodynamic properties were calculated using the quasi-harmonic Debye approximation to descript its stability.

Spin—Orbit Coupling in Single-Walled Gold Nanotubes

The effect of spin—orbit coupling on the electron levels of (5, 3), (8, 7), (11, 3), (18, 11), (10, 5), (8, 8), and (13, 0) gold nanotubes of various diameters and chirality was studied in the framework of the relativistic version of the linear augmented cylindrical wave method. Spin-dependent band structures and electron state densities were calculated. Spin—orbit coupling is manifested as splitting of nonrelativistic dispersion curves. For the dispersion curve that crosses the Fermi level in the (5, 3) tube of the minimum radius, this splitting reaches 0.5 eV and decreases on going to low-lying valence band states. An increase in the radius and a decrease in the cylindrical surface curvature of these nanotubes suppress the spin—orbit splitting. All tubes possess a metal type band structure in which the number of conduction channels increases with increasing radius of the nanotube.

Electronic properties of zigzag ZnO nanoribbons with hydrogen and magnesium passivations

In this study, the electronic properties of ZnO nanoribbons with zigzag edges (ZZnONr) have been investigated with Density Functional Theory (DFT). After a geometric optimization, the electronic band structures, the density of states (DOS) of ZZnONr passivated with Hydrogen (H) and Magnesium (Mg) atoms were calculated ZZnONr. It is shown that the increasing width of ZZnONrs has led to a decrement in energy band gap of the studied structures. While ZZnONr passivated with Mg for Zn-rich edge have not been shown a spin dependency, the structure passivated with Mg for O-rich edge have exhibited spin-dependent band structure. The energetically most stable structures have been determined as ZZnONr passivated with Mg for Zn-rich edge. ZZnONr passivated with Mg atoms for both edges have a graphene-like band structure especially for 8 and 10 atom width structures and this property of ZZnONrs could be important in terms of the electron transport for ZZnONrs.

Half-metallic property of the bulk and (001) surfaces of MNaCs (M = P, As) half-Heusler alloys: A density functional theory approach

The structural, electronic and half-metallic properties of bulk and (001) surfaces of MNaCs (M = P, As) half-Heusler alloys are investigated. The half-metallic property have been observed in both of these materials. The spin-flip gaps of PNaCs and AsNaCs are found to be 0.25 and 0.21 eV, and the Curie temperatures are estimated to be 478.24 and 474.07 K within the mean field approximation, respectively. The mechanisms of half-metallicity in these materials are studied by considering the spin-dependent band structures and the atomic density of states. The preservation of the half-metallic ferromagnetism under stress are also investigated. The symmetric slab model is employed for the investigation of the (001) surfaces of the compounds because the electron spin polarization at the bulk of the materials does not guarantee the spin-polarization at the surfaces of them. It turns out that the half-metallic ferromagnetism is well preserved for P (As)-terminated surfaces, but it is removed at the NaCs-terminated surfaces of both of the compounds.

Intrinsic transmission magnetic circular dichroism spectra of GaMnAs

Transmission magnetic circular dichroism (MCD) spectroscopy has been widely used to reveal the spin-dependent band structure of ferromagnetic semiconductors. In these previous studies, some band pictures have been proposed from the spectral shapes observed in transmission MCD; however, extrinsic signals originating from optical interference have not been appropriately considered. In this study, we calculate the MCD spectra taking into account the optical interference of the layered structure of samples and show that the spectral shape of MCD is strongly influenced by optical interference. To correctly understand the transmission MCD, we also calculate the intrinsic MCD spectra of GaMnAs that are not influenced by the optical interference. The spectral shape of the intrinsic MCD can be explained by the characteristic band structure of GaMnAs, that is, the spin-polarized valence band and the impurity band existing above the valence band top.