Spin-resolved Band Structure Research Articles

Ab-initio DFT＋[formula omitted] study on the electronic correlation in multiferroic XY-antiferromagnetic Ba2CoGe2O7

Ab-initio density functional theory (DFT)＋U has been used to study the spin-resolved electronic band structure and the partial density of states of the multiferroic XY-antiferromagnetic Ba2CoGe2O7. Using the constrained random-phase approximation (cRPA) method, the value of Hubbard U and Hund’s coupling JH has been determined and plugged into the further dynamical mean field theory (DMFT) calculations. The strong metal-ligand hybridization between Co-3d and O-2p orbitals in the CoO4 tetrahedron has been demonstrated via DFT and DFT＋DMFT calculations. The calculated indirect band gap in the antiferromagnetic state without and with U (=5 eV) correction is found to be 0.67 and 2.71 eV, respectively. The highest calculated ordered magnetic moment of 2.7 μB/Co2+ is close to the reported experimental value. The presented DFT calculations based on the different orbital models brings the underlying strong electronic correlation in the Ba2CoGe2O7.

Insight into electronic, magnetic and optical properties of KMnxNb1-xO3 compound

Density functional theory (DFT) based calculations are performed to study the physical features of Mn doped KNbO3. The spin resolved electronic band structure (BS) and density of states (DOS) are investigated that confirmed the half-metallic ferromagnetic (HMFM) character at x=12.5 and 25% Mn concentration. The energy gap of pure KNbO3 is found to majority influenced by Mn-3d states which introduces new states in the vicinity of Fermi level. The optical features (dielectric function, absorption coefficient, extinction coefficient, refractive index and optical conductivity) are examined to further reveal the role of Mn doping on the KNbO3 compound for optical devices. Finally in magnetic properties, the total magnetic moment of 2.98 and 3.68 μB which is mainly originated from Mn-3d along with weak contribution from K, Nb, and O. Results revealed that KMnxNb1-xO3 compound is a favorable candidate for optoelectronics and spintronics gadgets applications.

Spin-to-charge conversion origin in graphene on ferromagnetic substrate revealed: Rashba effects at Dirac point

Spin-to-charge current conversion (SCC) by inverse Rashba Edelstein effect (IREE) has been recently observed by spin-pumping experiment in single layer graphene (SLG) placed on ferromagnetic substrate composed mostly of Ni. However, a prior angle-resolved photoemission spectroscopy (ARPES) shows a negligible Rashba splitting at Γ−M, unsupportive of SCC by IREE. In this work, using density functional theory with spin-orbit coupling (DFT + SOC) calculations, we obtained the Rashba-type spin-resolved bandstructure on relevant symmetric k-points of SLG on Ni(111). We found no Rashba splitting at Γ−M confirming ARPES, however, we discovered considerable Rashba splittings in the dispersions along M−K−M, that is, involving the Dirac point, paving the way for SCC by IREE. Thus, for the first time, this work has reconciled the above seemingly contradicting spin-pumping and ARPES experiments, revealed the physical and magnetic origin of SCC by IREE and proposed means to increase the SCC coefficient without the use of heavy precious metals.

Development of deflector mode for spin-resolved time-of-flight photoemission spectroscopy.

Spin- and angle-resolved photoemission spectroscopy ("spin-ARPES") is a powerful technique for probing the spin degree-of-freedom in materials with nontrivial topology, magnetism, and strong correlations. Spin-ARPES faces severe experimental challenges compared to conventional ARPES attributed to the dramatically lower efficiency of its detection mechanism, making it crucial for instrumentation developments that improve the overall performance of the technique. In this paper, we demonstrate the functionality of our spin-ARPES setup based on time-of-flight spectroscopy and introduce our recent development of an electrostatic deflector mode to map out spin-resolved band structures without sample rotation. We demonstrate the functionality by presenting the spin-resolved spectra of the topological insulator Bi2Te3 and describe in detail the spectrum calibrations based on numerical simulations. By implementing the deflector mode, we minimize the need for sample rotation during measurements, hence improving the overall efficiency of experiments on small or inhomogeneous samples.

ARPES studies of the ground state electronic properties of the van der Waals transition metal trichalcogenide CoPS[formula omitted

The electronic structure of a wide bandgap van der Waals antiferromagnetic material CoPS3 (transition metal phosphorus trichalcogenide) is studied using angle-resolved photoelectron spectroscopy at room temperature which is well above the TN transition temperature for this compound. The observed dispersion of the electronic states in the valence band is correctly described using spin-resolved band structure. This observation points to the importance of the local electron–electron correlations and fluctuations for the description of the electronic and magnetic properties of transition metal phosphorus trichalcogenides and draws further ideas for the studies of electronic structure of CoPS3 and other similar materials.

Spin-Resolved Band Structure of Hoffman Clathrate [Fe(pz)2Pt(CN)4] as an Essential Tool to Predict Optical Spectra of Metal–Organic Frameworks

Paramount spin-crossover properties of the 3D-Hoffman metalorganic framework (MOF) [Fe(pz)2Pt(CN)4] are generally described on the basis of the ligand field theory, which provides adequate insight into theoretical and simulation analysis of spintronic complexes. However, the ligand field approximation does not take into account the 3D periodicity of the actual complex lattice and surface effects and therefore cannot predict a full-scale periodic structure without utilizing more advanced methods. Therefore, in this paper, the electronic properties of the exemplar MOF were analyzed from the band structure perspective in low-spin (LS) and high-spin (HS) states. The density-of-states spectra determined for both spin-up and spin-down electrons of Fe d6 orbitals indicate spin-orbital splitting and delocalization for HS due to spin polarization in the iron atom ligand field. Presence of the surface states in the real crystal causes a red shift of the metal-metal charge transfer (MMCT) and metal-ligand charge transfer (MLCT) peaks for both HS and LS states. The addition of residual water molecules and disorder among the pyrazine rings reveal additional influences on the positions of the pyrazine band and, therefore, on the absorption spectra of the crystal. The results show a magnification of the peak correlated with the MLCT in the HS state and a significant red shift of the LS characteristic absorption band. The presented approach involving band structure analysis delivers a more complete image of the electronic properties of the [Fe(pz)2Pt(CN)4] crystalline network and can be a landmark for insightful studies of other MOFs.

Novel germanene-arsenene and germanene-antimonene lateral heterostructures: interline-dependent electronic and magnetic properties.

Seamlessly stitching two-dimensional (2D) materials may lead to the emergence of novel properties triggered by the interactions at the interface. In this work, a series of 2D lateral heterostructures (LHSs), namely germanene-arsenene (Gem-As8-m) and germanene-antimonene (Gem-Sb8-m), are investigated using first-principles calculations. The results demonstrate a strong interline-dependence of the electronic and magnetic properties. Specifically, the LHS formation along an armchair line preserves the non-magnetic nature of the original materials. However, this is an efficient approach to open the electronic band gap of the germanene monolayer, where band gaps as large as 0.74 and 0.76 eV are induced for Ge2-As6 and Ge2-Sb6 LHSs, respectively. Meanwhile, magnetism may appear in the zigzag-LHSs depending on the chemical composition (m = 3, 4, 5, and 6 for germanene-arsenene and m = 2, 3, 4, 5, and 6 for germanene-antimonene), where total magnetic moments between 0.13 and 0.50 μB are obtained. Herein, magnetic properties are produced mainly by the spin-up state of Ge atoms at the interface, where a small contribution comes from As(Sb) atoms. Spin-resolved band structures show a multivalley profile in both the valence band and the conduction band with a topological insulator-like behavior, where the interface states are derived mainly from the interface Ge-pz state. The results introduce new 2D lateral heterostructures with novel electronic and magnetic properties to allow new functionalities, which could be further explored for optoelectronic and spintronic applications.

Tuned physical characteristics of PbSe binary compound: a DFT study

Physical features of transition metal (TM) doped lead selenide, Pb1-xCrxSe, Pb1-xCoxSe and Pb1-xNixSe (x=0% and 25%) have been investigated by ab-inito method. The exchange correlation energy is computed by generalized gradient approximation (GGA). A direct band gap (Eg) of 0.35 eV has been observed for PbSe. The analysis of spin-resolved electronic band structure (BS) and density of states (DOS) reveal the half-metallic ferromagnetic (HMF) character of doped compounds. In addition, the calculated magnetic moments (μB) of Pb1-xCrxSe, Pb1-xCoxSe and Pb1-xNixSe compounds are found to arise due to doped transition metals and confirmed by 3D spin-polaized iso-surface density plots. The optical features including optical conductivity (), absorption coefficient, extinction coefficient k, refractivity R, dielectric function and refractive index n() have been calculated to envisage the optical response of given materials. Further, the BoltzTrap code has been implemented to probe the thermoelectric characteristics in term of power factor (PF), Seebeck coefficient (S), thermal and electrical conductivity. The outcomes of calculations divulge that Pb1-xXxSe (X=Cr, Co, Ni) would be suitable candidates for both optoelectronics and thermoelectric applications.

First-principles Calculations to Investigate Emerging Double Perovskites K2NaMoX6 (X=Cl, I) Compounds for Magnetic and Optoelectronic Applications

In the present work, the structural, electronic, optical and mechanical properties of lead free halide double perovskites (HDPs) K2NaMoX6 (X = I, Cl) are addressed by using density functional theory (DFT). The optimized structural parameters validate the stability of the magnetic states of K2NaMoX6 (X = I, Cl) compounds with magnetic moment of 3.0006 and 3.00001 μB, respectively. The stability of cubic phase of both compounds is justified by tolerance factor. Spin resolved band structure (BS) and density of states (DOS) demonstrate that K2NaMoCl6 and K2NaMoI6 are direct-gap semiconducting materials. Moreover, the computed elastic properties reveal the ductile and anisotropic nature of both compounds. The optical features such as, the absorption coefficient (α(ω)), real ϵ1(ω) and imaginary parts ϵ2(ω) of the dielectric function, optical conductivity (σ(ω)), refractive index (n(ω)), extinction coefficient (k(ω)) and reflectivity (R(ω)) are also computed. In optoelectronic devices, these HDPs have intriguing uses due to the excessive α(ω) and small reflection in the visible-UV span.

Multifunctional spintronic device based on zigzag SiC nanoribbon heterojunction via edge asymmetric dual-hydrogenation

The authors propose a method to obtain the multifunctional spintronic device by investigating the spin-resolved transport characteristics of zigzag SiC nanoribbon (zSiCNR) heterojunction via edge asymmetric dual-hydrogenation. The spin-resolved band structures show that the dual-hydrogenation on edge C or Si atoms all can change the initial metallicity of the pristine zSiCNR with the edge mono-hydrogenation to semiconductor in the presence of ferromagnetic field. The spin-resolved current-voltage characteristics of the zSiCNR heterojunction can show spin current rectification in the same rectify direction under the parallel magnetic field. The up-spin rectification ratio of our junction can be close to 10 13 at −0.5 V, which is much larger than rectification ratios of the previous junctions induced by the anti-parallel magnetic field. The zSiCNR heterojunction also exhibits a perfect spin filtering behavior with 100% spin filtering efficiency in both positive and negative bias regions under the anti-parallel magnetic field. More interestingly, the magnetoresistance is achieved by manipulating the external magnetic field in our zSiCNR heterojunction with the giant magnetoresistance ratio 5000% at 0.5 V. Therefore, the zSiCNR heterojunction via edge asymmetric dual-hydrogenation can be designed into the multifunctional spintronic devices, which has broad application prospects in the field of future spintronics. • Zigzag silicon carbon nanoribbon has potential in spin devices. • Giant spin current rectification is obtained in the presence of a ferromagnetic field. • Maximum spin current rectification ratios is closing to 10 13 . • Perfect spin filtering and magnetoresistance behaviors are also obtained.

Tunable magnetoelectric coupling and electrical features in an ultrathin Cr2Si2Te6/In2Se3 heterostructure.

Two-dimensional (2D) van der Waals (vdW) heterostructures based on multiferroic materials have potential applications in novel low-dimensional spintronic devices. In this work, we have investigated a strong magnetoelectric coupling and electrical dependence between single layer (1L) Cr2Si2Te6 and In2Se3. By switching the direction of ferroelectric polarization in In2Se3, we observed a significant magneto-crystalline anisotropy energy (MAE) enhancement of Cr2Si2Te6. The analysis of the spin-resolved orbital-decomposed band structure shows stronger magnetoelectric coupling between the In2Se3 and Cr2Si2Te6 layers. The modulation of the electrical features could also be achieved in the switching of the ferroelectric polarization. Furthermore, the switching of Ohmic-Schottky contacts in the heterojunction with different polarization states was successfully achieved under the effect of strain engineering. Based on these findings, we design a novel 2D ferroelectric-ferromagnetic heterojunction that exploits the controllability and nonvolatility of ferroelectrics to modulate the electrical properties of the device. These findings indicate the high application potential of Cr2Si2Te6/In2Se3 multiferroic heterojunctions in spintronics.

Spin-resolved band structures and transport properties of δ-graphyne nanoribbon with bilateral or unilateral fluorination

Among the graphyne family, δ-Graphyne is a new typical representative for instance. In this article, we have studied the spin-splitting phenomena in the band structures and transport properties of zigzag δ-graphyne nanoribbron (ZδGYNR) with edge fluorination. Our results show that the spin-splitting can be observed obviously in the ZδGYNRs with unilateral or bilateral edge fluorinations. Moreover, some distinct physical effects, such as spin-filtering, rectification and negative differential resistance, can be found in the proposed device models. Particularly, the efficiency of spin-filtering can approach to 100% in the antiparallel spin-configuration of the bilateral fluorination model, which would be capable of leading to promising applications in spintronics and nanodevices.

Ab-initio investigation of structural, mechanical, thermodynamic, electronic, magnetic and thermoelectric properties of half-metallic d0 half-Heusler alloys LiXSi (X=Ca, Sr)

Structural, mechanical, thermodynamic, electronic, and magnetic properties of LiXSi (X ​= ​Ca, Sr) d0 half-Heusler alloys have been evaluated by implementing the GGA-PBE approximation in the Density Functional Theory calculations. The Boltzmann transport theory has been implemented for examining the thermoelectric properties of the alloys. The spin-polarized calculations show that LiCaSi and LiSrSi crystallize in the ferromagnetic α-phase equilibrium states. Spin-resolved band structures depict complete spin polarization obtained at the Fermi level and confirm the true half-metallic nature of the alloys. The calculated total magnetic moment is 0.99 ​μB for LiCaSi and 1.00 ​μB for LiSrSi, which very closely follow the Slater-Pauling rule. The observed ferromagnetic characteristics arise mostly from the spin-polarization of the 2p states in Si for both alloys. The LiXSi (X ​= ​Ca, Sr) alloys are found to be mechanically stable according to the Born stability criteria for cubic structured systems. Both the alloys are predicted to be ductile in nature. Important thermodynamic properties such as Debye temperature and CV have been calculated by implementing the quasi-harmonic approximation. The calculations for the transport properties show that the alloys are p-type materials with high Seebeck coefficients and electrical conductivities. The dimensionless thermoelectric figure of merit obtained for both the alloys at 300K is close to unity, which confirms the high thermoelectric efficiency of the alloys.

Spin-dependent seebeck effect and pure spin current in ferromagnetic fluorinated boron nitride nanotubes

Based on the density functional theory combined with non-equilibrium Green's function formalism, we investigate the electronic structure and spin caloritronic transport properties of ferromagnetic fluorinated boron nitride nanotubes (F-BNNTs). The results show that these systems exhibit robust half-metallic feature and obvious spin-dependent Seebeck effect . Especially, pure spin current without charge current can be realized by tuning the temperature and temperature difference or by tuning the chirality of F-BNNT. The underlying mechanism is analyzed by the Fermi-Dirac distribution function, spin-resolved transmission spectra, band structures and current spectra. These results demonstrate that the ferromagnetic F-BNNTs hold great potential for spin caloritronics and ultra-low-energy-consumption nanoelectronic devices. • Electronic structure and spin caloritronic transport properties of F-BNNTs are investigated. • F-BNNTs exhibit robust half-metallic feature and obvious Spin-dependent Seebeck effect. • Pure spin current is realized by tuning the temperature and temperature difference. • Pure spin current is realized by tuning the chirality of F-BNNT.

Robust stability, half-metallic ferrimagnetism and thermoelectric properties of new quaternary Heusler material: A first principles approach

Like full or half-heusler materials, equiatomic quaternary Heuslers (EQH) also display various intriguing physical properties. We carried out the strict and rigorous density functional theory calculations to estimate the stability of novel ferrimagnetic FeMnTaAl alloy. In this work, we considered the thermodynamic, energetic, dynamic and mechanical stability criteria, by evaluating the formation energy, phonon dispersion and elastic constants, respectively, which thereby suggest that the synthesis of FeMnTaAl as bulk phase is likely. Later, the electronic structure, magnetic and transport properties are determined from the ground state parameters. After the structural optimizations, the half-metallic character from spin resolved band structures and local spin moments (1 μB) potentially felicitate its spintronic applications. Conservative estimates of Seebeck coefficient (~85 μV/K at 900 K), lattice thermal conductivity (2.8 W/mK at 300 K) and figure of merit (0.03 at 900 K) have also been put forward in this report. The overall structural stability, ferrimagnetism with large TC accompanied by transport properties will possibly enact the experimental realization for magnetic, thermoelectric or spintronic impressions of this material in future.

Molecular logic gates based on spin caloritronic transport properties of Mn phthalocyanine nanoribbon

Based on the density functional theory along with nonequilibrium Green's function technique, we investigate the spin caloritronic transport properties of ferromagnetic one-dimensional Mn phthalocyanine nanoribbon under different magnetic configurations. The results demonstrate the thermally-driven spin-dependent currents depend strongly on the choice of magnetic configuration. The underlying mechanism is analyzed by the Fermi-Dirac distribution function, spin-resolved transmission spectra, band structures and current spectra. And based on those intriguing spin caloritronic transport properties, we design thermal spin AND, OR and NOT molecular logic gates.

Room-temperature multiferroicity and diversified magnetoelectric couplings in 2D materials.

Multiferroics are rare in nature due to the mutual exclusive origins of magnetism and ferroelectricity. The simultaneous coexistence of robust magnetism/ferroelectricity and strong magnetoelectric coupling in single multiferroics is hitherto unreported, which may also be attributed to their potential conflictions. In this paper, we show the first-principles evidence of such desired coexistence in ultrathin-layer CuCrS2 and CuCrSe2. The vertical ferroelectricity is neither induced by an empty d shell nor spin-driven, giving rise to an alternative possibility of resolving those intrinsic exclusions and contradictions. Compared with their bulk phases, the ferromagnetism in the thin-layer structures (two–six layers) can be greatly stabilized due to the enhanced carrier density and orbital shifting by vertical polarization, and the Curie temperatures of both ferromagnetism and ferroelectricity can be above room temperature. Moreover, a considerable net magnetization can be reversed upon ferroelectric switching, where the change in spin-resolved band structure also renders efficient ‘magnetic reading + electrical writing’. The thickness-different layers may even exhibit diversified types of magnetoelectric coupling, which both enriches the physics of multiferroics and facilitates their practical applications.

Study of ferromagnetism, spin-polarization, thermoelectrics and thermodynamics of layered perovskite Ba2FeMnO6 under pressure and temperature

A systematic evaluation of experimentally studied prototypical magnetic, Fm-3m (225) structured double perovskite Ba2FeMnO6 has been explored first time theoritically to investigate the electronic structure, magnetic, thermoelectric and thermodynamic properties. The optimized lattice constant by structural optimization is found to be consistent and in rational accord with the experimental lattice constant. The magnetic interactions were taken into consideration, among which ferromagnetic configuration was found stable. Band structure is predicted using the more sophisticated GGA + Hubbard model, where we find density of states feature half-metallic nature with a direct energy band gap of 3 eV. In addition, semi-classical Boltzmann theory for heat transport is used to check the applicability of the material for thermoelectric applications. Remarkably, thermoelectric Seebeck coefficient as well as spin resolved band structures, reflects the majority of p-type conduction of charge carriers as heat transporters. The conductivity due to phonon lattice vibrations show a decresing trend along the selected range of temperature. Also, complete and precise description of thermo-physical behavior of the vital quantities like Debye temperature, thermal expansion, Grüneisen parameter and specific heat were examined to check its thermodynamical stability against temperature and pressure variation.

Spin Caloritronic Transport of Tree-Saw Graphene Nanoribbons**Supported by the Natural Science Foundation of Shandong Province under Grant No ZR2016AM11.

Using density functional theory combined with non-equilibrium Greenʼs function method, we investigate the spin caloritronic transport properties of tree-saw graphene nanoribbons. These systems have stable ferromagnetic ground states with a high Curie temperature that is far above room temperature and exhibit obvious spin-Seebeck effect. Moreover, thermal colossal magnetoresistance up to 1020% can be achieved by the external magnetic field modulation. The underlying mechanism is analyzed by spin-resolved transmission spectra, current spectra and band structures.

Influence of interfaces on the phonon density of states of nanoscale metallic multilayers: Phonon confinement and localization

Isotope-selective $^{57}\mathrm{Fe}$ nuclear resonant inelastic x-ray scattering (NRIXS) measurements and atomic-layer resolved density functional theory (DFT) calculations were used to investigate the effect of interfaces on the vibrational (phonon) density of states (VDOS) of (001)-oriented nanoscale Fe/Ag and Fe/Cr multilayers. The multilayers in the experiment contained isotopically enriched $^{57}\mathrm{Fe}$ monolayers as probe layers located either at the Fe/Ag or Fe/Cr interfaces or in the center of the Fe films. This allows probing of the vibrational dynamics of Fe sites either at the buried interfaces or in the center of the Fe films. For Fe/Ag multilayers, distinct differences were observed experimentally between the Fe-partial VDOS at the interface and in the center. At the Fe/Ag interface, the high-energy longitudinal-acoustic (LA) phonon peak of Fe near $\ensuremath{\sim}35$ meV is suppressed and slightly shifted to lower energy, and the low-energy part of the VDOS below $\ensuremath{\sim}20$ meV is drastically enhanced, as compared to the Fe-specific VDOS in the center Fe layers or in bulk Fe. Similar phenomena are found to a less degree in the Fe/Cr multilayers. The measured Fe-partial VDOS was used to determine the Fe site-selective vibrational thermodynamic properties of the multilayers. Our theoretical findings for the layer-dependent VDOS of the multilayers are in qualitative agreement with the experimental results obtained by NRIXS. For Fe/Ag multilayers, which are characterized by a large atomic mass ratio, the experimental and theoretical results demonstrate phonon confinement in the Fe layers and phonon localization at the Fe/Ag interfaces due to the energy mismatch between Ag and Fe LA phonons. These phenomena are reduced or suppressed in the Fe/Cr multilayers with their about equal atomic masses. Moreover, direction-projected Fe VDOS along the (nearly in-plane) incident x-ray beam was computed in order to address the intrinsic vibrational anisotropy of the Fe/Ag multilayer. We have also performed spin-resolved electronic band structure (DFT) calculations, predicting an enhanced magnetic moment $({\ensuremath{\mu}}_{\mathrm{Fe}}=2.8\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}})$ of the interfacial Fe atoms and a high electron spin polarization (79%) at the Fermi energy for the Fe/Ag interface, as compared to the case of Fe center layers. This is a result of charge transfer from Fe to Ag at the interface. On the contrary, Cr tends to donate electrons to Fe, thus reducing the interfacial Fe moment $({\ensuremath{\mu}}_{\mathrm{Fe}}=1.9\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}})$. This implies strong chemical bonding at the Fe/Ag and Fe/Cr interfaces, affecting the interfacial VDOS.