Half-metallic Band Structure Research Articles

Adsorption effects of acetone and acetonitrile on defected penta-PdSe2 nanoribbons: a DFT study.

Using DFT calculations, the structural and electronic properties of the ZZ7 p-PdSe2 nanoribbons (ZZ7) with the four kinds of vacancy defects, including ZZ7-VPd, ZZ7-VSe, ZZ7-VPd+Se, and ZZ7-V2Se are studied, in which their stability, diverse geometries, and altered electronic properties are determined through the formation energies, optimal structural parameters, electronic band structures, and DOSs. Specifically, the formation energies of all studied systems show significant negative values around -3.9 eV, evidencing their good thermal stability. The geometries of four defective structures exhibit different diversification, whereas only the ZZ7-V2Se structure possesses the highly enhanced feature, identified as the most effective substrate for the acetone and acetonitrile adsorption. On the electronic behaviors, the ZZ7 band structure displays the nonmagnetic metallic characteristics that become the ferromagnetic half-metallic band structures for the ZZ7-VPd and ZZ7-VSe and the ferromagnetic semi-metallic band structures for the ZZ7-VPd+Se and ZZ7-V2Se. For adsorption of the acetone and acetonitrile on the ZZ7-V2Se structure, the energetic stability, adsorption sites, adsorption distances, charge transfers, and electronic characteristics of the adsorbed systems are determined by the adsorption energies, optimal adsorption sites, adsorption distances, Mulliken populations, and DOSs. The adsorption energies of the acetone- and acetonitrile-adsorbed ZZ7-V2Se systems display significant values at -1.2 eV and -0.86 eV at the preferable sites of 8 and 11, respectively, indicating their great adsorption ability. The adsorption mechanism of the acetone- and acetonitrile-adsorbed systems belongs to the physisorption owing to absence of chemical bonds, in which the bond lengths of the ZZ7-V2Se substrate show a very small deviation. Under the acetone and acetonitrile adsorptions, the ferromagnetic semi-metallic DOSs of the ZZ7-V2Se become the ferromagnetic half-metallic DOSs for the ZZ7-V2Se-acetone-8 and the ferromagnetic semiconducting DOSs for the ZZ7-V2Se-acetonitrile-11. Our systematic results can provide a complete understanding of the acetone- and acetonitrile adsorptions on the potential ZZ7-V2Se structure, which is very useful for nanosensor application.

Ab-initio study of quaternary Heusler alloys LiAEFeSb (AE = Be, Mg, Ca, Sr or Ba) and prediction of half-metallicity in LiSrFeSb and LiBaFeSb

The quaternary Heusler alloys with composition LiAEFeSb have been studied in this manuscript (AE = Alkaline Earth elements Be, Mg, Ca, Sr and Ba) for their potential applications in spintronics. All the investigations have been performed by employing density functional theory. A systematic comparison of results obtained within local density approximation (LDA) and the generalized gradient approximation (GGA) done. Our calculations reveal that all the studied alloys have lowest energy in type-I arrangement of basis and exhibit interesting electronic and magnetic properties. All the alloys exhibit a stable ferromagnetic ground state. Fixed spin moment calculations rule out existence of any other local magnetic minima. The phonon dispersions show that all the alloys except LiBeFeSb are dynamically stable. Notably, LiSrFeSb and LiBaFeSb exhibit half-metallic electronic band structure and 100 % spin polarization making them suitable choice for promising spintronic applications such as spin filter and detectors.

High Chern numbers in a perovskite-derived dice lattice (LaXO3)3/(LaAlO3)3(111) with X = Ti, Mn and Co

The dice lattice, containing a stack of three triangular lattices, has been proposed to exhibit nontrivial flat bands with nonzero Chern numbers, but unlike the honeycomb lattice it is much less studied. By employing density-functional theory (DFT) calculations with an on-site Coulomb repulsion term, we explore systematically the electronic and topological properties of (LaXO3)3/(LaAlO3)3(111) superlattices with X = Ti, Mn and Co, where a LaAlO3 trilayer spacer confines the LaXO3 (LXO) dice lattice. In the absence of spin-orbit coupling (SOC) with symmetry constrained to P3, the ferromagnetic (FM) phase of the LXO(111) trilayers exhibits a half-metallic band structure with multiple Dirac crossings and coupled electron-hole pockets around the Fermi energy. Symmetry lowering induces a significant rearrangement of bands and triggers a metal-to-insulator transition. Inclusion of SOC leads to a substantial anomalous Hall conductivity (AHC) around the Fermi energy reaching values up to sim -3e^2/h for X = Mn and Co in P3 symmetry and both in- and out-of-plane magnetization directions in the first case and along [001] in the latter. The dice lattice emerges as a promising playground to realise nontrivial topological phases with high Chern numbers.

Sign change of intrinsic domain wall resistance in epitaxial Heusler alloy Co[formula omitted]MnAl thin films

The investigation of magnetic domain wall resistance (DWR) in epitaxial Co2MnAl (CMA) thin films, a Heusler alloy, has revealed a remarkable phenomenon of sign change. This intriguing behavior is attributed to the half-metallic band structure with high spin polarization, as verified by negative anisotropic magnetoresistance in the two-current model. In this way, the scattering relaxation time for the majority and minority electrons, which is primarily determined by the density of states of majority and minority electrons, undergoes a dramatic change in the vicinity of the half-metallic band gap. This results in an unusual upturned relaxation time ratio, leading to the sign change of intrinsic DWR. These findings deepen our understanding of the intricate dynamics of spin-dependent phenomena in half metals and shed light on the entangled magnetoresistance in Heusler alloy with high spin polarization.

Theoretical study on spin-dependent zigzag-direction thermoelectric transport properties of Mn-doped blue phosphorene

With the increasing demand for energy, it has become imperative to investigate the thermoelectric properties that can be beneficial to directly converting heat into electric energy. Here, we theoretically study the thermoelectric transport of the Mn-doped blue phosphorene (blue-P) along the zigzag direction. We show that the spin-polarized electronic transport in the blue-P can be produced by the Mn-doping induced half-metallic energy band structure, and the Seebeck coefficients can take positive and negative values, indicating that the main carriers may be holes and electrons. Thus, the spin-down, spin, and charge Seebeck coefficients show a high peak and a deep valley, while the spin and charge thermoelectric figures of merit show two wide peaks. Moreover, the spin and charge thermoelectric figures of merit are found to be so large that the Mn-doped blue-P along the zigzag direction can be used as good thermoelectric materials. In addition, we consider the effect of the doping concentration on the electronic structure and thermoelectric transport properties. This research should be an important reference for designing spin caloritronic and thermoelectric devices.

Band-folding-driven high tunnel magnetoresistance ratios in (111)-oriented junctions with SrTiO3 barriers

We theoretically study the tunnel magnetoresistance (TMR) effect in (111)-oriented magnetic tunnel junctions (MTJs) with SrTiO$_{3}$ barriers, Co/SrTiO$_{3}$/Co(111) and Ni/SrTiO$_{3}$/Ni(111). Our analysis combining the first-principles calculation and the Landauer formula shows that the Co-based MTJ has a high TMR ratio over 500%, while the Ni-based MTJ has a smaller value (290%). Since the in-plane lattice periodicity of SrTiO$_{3}$ is about twice that of the primitive cell of fcc Co (Ni), the original bands of Co (Ni) are folded in the $k_x$-$k_y$ plane corresponding to the $ab$ plane of the MTJ supercell. We find that this band folding gives a half-metallic band structure in the $\Lambda_1$ state of Co (Ni) and the coherent tunneling of such a half-metallic $\Lambda_1$ state yields a high TMR ratio. We also reveal that the difference in the TMR ratio between the Co- and Ni-based MTJs can be understood by different $s$-orbital weights in the $\Lambda_1$ band at the Fermi level.

Oxygen-vacancy-induced structural transition and enhanced magnetism in Sc, Fe-codoped SrTiO3: A theoretical study*

The spin-polarized electronic structure and magnetism of (Fe + Sc)-doped SrTiO3 (STO) with and without oxygen vacancy are investigated through first principles calculations. The computations show that codoping with Fe and Sc leads to the formation of spin-splitting half-metallic electronic band structure and induces a total magnetic moment of about 3.58 μB/supercell. The magnetism is formed by the strong hybridization between Fe 3d and O 2p states. A transition from half-metallic to semiconductor is observed with further introducing an oxygen vacancy. The magnetic moment of (Fe + Sc)-STO with oxygen vacancy is enhanced to 5 μB/supercell due to vacancy-induced structure distortion and increased magnetization.

Electronic band structure and magnetism of CoFeV0.5Mn0.5Si

Half-metallic Heusler alloys have attracted significant attention due to their potential application in spin-transport-based devices. We have synthesized one such alloy, CoFeV0.5Mn0.5Si, using arc melting and high-vacuum annealing at 600 °C for 24 hours. First principles calculation indicates that CoFeV0.5Mn0.5Si shows a nearly half-metallic band structure with a degree of spin polarization of about 93%. In addition, this value can be enhanced by the application of tensile strain. The room temperature x-ray diffraction patterns are indexed with the cubic crystal structure without secondary phases. The annealed sample shows ferromagnetic order with the Curie temperature well above room temperature (Tc = 657 K) and a saturation magnetization of about 92 emu/g. Our results indicate that CoFeV0.5Mn0.5Si has a potential for room temperature spin-transport-based devices.

Electronic, structural and magnetic properties of Mn(1+x)Pt(1-x)Sb

Electronic and magnetic properties of half-metallic Heusler alloys can be modified by tuning their chemical compositions. We have carried out a combined theoretical and experimental investigation of Mn(1+x)Pt(1-x)Sb (0 ≤ x ≤ 0.5) alloys. Our first-principles calculations indicate that the stoichiometric MnPtSb exhibits nearly half-metallic band structure, but a robust half-metallicity can be achieved in Mn-rich compositions Mn(1+x)Pt(1-x)Sb (0 ≤ x ≤ 0.5) with x = 0.25 and higher in their cubic structures. In addition, while MnPtSb exhibits ferromagnetic alignment, Mn(1+x)Pt(1-x)Sb are ferrimagnetic for all non-zero values of x. We have also synthesized cubic MnPtSb and Mn1.25Pt0.75Sb alloys using arc melting and annealing. The magnetic properties of these alloys are consistent with our theoretical predictions. These results indicate that the Mn-rich Mn(1+x)Pt(1-x)Sb alloys have potential for spin-transport-based devices.

Visualizing Half-Metallic Bulk Band Structure with Multiple Weyl Cones of the Heusler Ferromagnet.

Using a well-focused soft x-ray synchrotron radiation beam, angle-resolved photoelectron spectroscopy was applied to a full-Heusler-type Co_{2}MnGe alloy to elucidate its bulk band structure. A large parabolic band at the Brillouin zone center and several bands that cross the Fermi level near the Brillouin zone boundary were identified in line with the results from first-principles calculations. These Fermi-level crossings are ascribed to majority spin bands that are responsible for electron transport with extremely high spin polarization especially along the direction perpendicular to the interface of magnetoresistive devices. The spectroscopy confirms there is no contribution of the minority spin bands to the Fermi surface, signifying half-metallicity for the alloy. Furthermore, two topological Weyl cones with band crossing points were identified around the X point, yielding the conclusion that Co_{2}MnGe could exhibit topologically meaningful behavior such as large anomalous Hall and Nernst effects driven by the Berry flux in its half-metallic band structure.

Ferromagnetic hybrid nodal loop and switchable type-I and type-II Weyl fermions in two dimensions

As a novel type of fermionic state, hybrid nodal loop with the coexistence of both type-I and type- II band crossings has attracted intense research interest. However, it remains a challenge to realize hybrid nodal loop in both two-dimensional (2D) materials and in ferromagnetic (FM) materials. Here, we propose the first FM hybrid nodal loop in 2D CrN monolayer. We show that the material has a high Curie temperature (> 600 K) FM ground state, with the out-of-plane [001] magnetization. It shows a half-metallic band structure with two bands in the spin-up channel crossing each other near the Fermi level. These bands produce both type-I and type-II band crossings, which form a fully spin-polarized hybrid nodal loop. We find the nodal loop is protected by the mirror symmetry and robust against spin-orbit coupling (SOC). An effective Hamiltonian characterizing the hybrid nodal loop is established. We further find the configuration of nodal loop can be shifted under external perturbations such as strain. Most remarkably, we demonstrate that both type-I and type-II Weyl nodes can be realized from such FM hybrid nodal loop by simply shifting the magnetization from out-of-plane to in-plane. Our work provides an excellent candidate to realize FM hybrid nodal loop and Weyl fermions in 2D material, and is also promising for related topological applications with their intriguing properties.

Graphene/Half-Metallic Heusler Alloy: A Novel Heterostructure toward High-Performance Graphene Spintronic Devices.

Graphene-based vertical spin valves (SVs) are expected to offer a large magnetoresistance effect without impairing the electrical conductivity, which can pave the way for the next generation of high-speed and low-power-consumption storage and memory technologies. However, the graphene-based vertical SV has failed to prove its competence due to the lack of a graphene/ferromagnet heterostructure, which can provide highly efficient spin transport. Herein, the synthesis and spin-dependent electronic properties of a novel heterostructure consisting of single-layer graphene (SLG) and a half-metallic Co2 Fe(Ge0.5 Ga0.5 ) (CFGG) Heusler alloy ferromagnet are reported. The growth of high-quality SLG with complete coverage by ultrahigh-vacuum chemical vapor deposition on a magnetron-sputtered single-crystalline CFGG thin film is demonstrated. The quasi-free-standing nature of SLG and robust magnetism of CFGG at the SLG/CFGG interface are revealed through depth-resolved X-ray magnetic circular dichroism spectroscopy. Density functional theory (DFT) calculation results indicate that the inherent electronic properties of SLG and CFGG such as the linear Dirac band and half-metallic band structure are preserved in the vicinity of the interface. These exciting findings suggest that the SLG/CFGG heterostructure possesses distinctive advantages over other reported graphene/ferromagnet heterostructures, for realizing effective transport of highly spin-polarized electrons in graphene-based vertical SV and other advanced spintronic devices.

Experimental realization and magnetotransport properties of half-metallic Fe2Si

Thin films of the high Curie temperature intermetallic ferromagnet β-Fe2Si were synthesized via molecular beam epitaxy. Investigation using X-ray diffraction and atomic force microscopy shows a hexagonal crystal structure and a smooth topography. Theoretically, Fe2Si has been predicted to exhibit uniquely desirable magnetotransport properties. We report on these properties experimentally, including the ordinary Hall coefficient R0 and anomalous Hall resistivity ρxyAH. The compound is found to be a soft Heisenberg ferromagnet with temperature dependent magnetization based on the thermal excitation of spin waves. We present a detailed look into the contributions to its longitudinal resistivity, which due to the presence of a spin-flip gap ΔkB, indicating a half-metallic band structure. The correct scaling relations between these components of the resistivity tensor (ρxx and ρxy) are also discussed.

New [formula omitted]-type half-metal MnBO3 with remarkable multiple Dirac-like band crossings: Effects of uniform strain, vacancies, spin–orbit coupling, and hole and electron doping on its electronic structures

Very recently, two R3−c Dirac half-metal materials, LaMnO3 and MnF3, were found and investigated by Du et al. via first principles. They stated that these types of materials with half-metallic band structures and multiple linear band dispersions might exhibit excellent 100% spin polarization and ultrafast electron transport. However, the application of MnF3 material in the field of spintronics is limited owing to its low Curie temperature (Tc). In this work, we proposed a new half-metal material—MnBO3. This material satisfies two demands at the same time—it is a half-metal with a high Tc, and it has multiple nearly linear band crossings. The effects of the uniform strain, vacancies, spin–orbit coupling, as well as hole and electron doping on its electronic structures have been discussed in detail. Furthermore, to better study its specific behaviors under extreme conditions, such as high temperature or pressure, we also investigated the thermodynamic properties of MnBO3 through the quasi-harmonic Debye model. Finally, its thermal stability at room temperature has been proved in this article by means of ab initio molecular dynamics (AIMD) simulations. We hope that MnBO3 can attract more attention for R3−c-type half-metallic materials with linear band crossings and a high Curie temperature in experimental and theoretical areas.

Half-metallic fully compensated ferrimagnetism and multifunctional spin transport properties of Mn3Al

The complete (100%) spin polarization, zero net magnetic moment and high Curie temperature (605 K) make the recently fabricated half-metallic fully compensated ferrimagnet Mn3Al a promising spintronic material. In order to explore the potential applications in spintronic devices, in this work, we give a theoretical analysis for the Mn3Al/GaAs(0 0 1) heterostructure and the Mn3Al/GaAs/Mn3Al(0 0 1) magnetic tunnel junction. Using the first-principles calculations combined with nonequilibrium Green’s function method, we demonstrate from the calculated bias-dependent spin transport properties that the heterostructure exhibits perfect spin filtering effect and spin diode effect, and the magnetic tunnel junction behaves a large tunnel magnetoresistance ratio (up to 10 900%). The physical origins of these versatile spin transport properties are discussed in terms of the half-metallic band structure, the spin-dependent transmission spectra and the band-to-band transmission theory.

Development of half metallicity within mixed magnetic phase of Cu1−xCoxMnSb alloy

Cubic half-Heusler Cu1−xCoxMnSb () compounds have been investigated both experimentally and theoretically for their magnetic, transport and electronic properties in search of possible half metallic antiferromagnetism. The systems (Cu,Co)MnSb are of particular interest as the end member alloys CuMnSb and CoMnSb are semi metallic (SM) antiferromagnetic (AFM) and half metallic (HM) ferromagnetic (FM), respectively. Clearly, Co-doping at the Cu-site of CuMnSb introduces changes in the carrier concentration at the Fermi level that may lead to half metallic ground state but there remains a persistent controversy whether the AFM to FM transition occurs simultaneously. Our experimental results reveal that the AFM to FM magnetic transition occurs through a percolation mechanism where Co-substitution gradually suppresses the AFM phase and forces FM polarization around every dopant cobalt. As a result a mixed magnetic phase is realized within this composition range while a nearly HM band structure is developed already at the 10% Co-doping. Absence of T2 dependence in the resistivity variation at low T-region serves as an indirect proof of opening up an energy gap at the Fermi surface in one of the spin channels. This is further corroborated by the ab initio electronic structure calculations that suggests that a nearly ferromagnetic half-metallic ground state is stabilized by Sb-p holes produced upon Co doping.

Magnetic and magnetocaloric properties of Co2-xFexVGa Heusler alloys

The magnetic and magnetocaloric properties of iron-substituted Co2VGa alloys, Co2-xFexVGa (x = 0, 0.1, 0.15, 0.2, 0.3), were investigated. The Fe-substituted samples, prepared by arc melting, melt spinning, and annealing, crystallized in the L21 Heusler structure, without any secondary phases. The Curie temperature and high-field magnetization at 50 K decreased from 345 K and 44 emu/g (1.90 μB/f.u.) for Co2VGa to 275 K and 39 emu/g (1.66 μB/f.u.) for Co1.7Fe0.3VGa, respectively, but the maximum entropy change remained almost insensitive to Fe concentration for x ≤ 0.2, the highest value being 3.3 J/kgK at 7 T for Co1.85Fe0.15VGa. First-principle calculations show that Co2VGa retains its half-metallic band structure until at least 30% of the cobalt atoms are replaced by Fe atoms. The wide operating temperature window near room temperature and the lack of thermal and magnetic hysteresis are the interesting features of these materials for application in room-temperature magnetic refrigeration.

Robust half-metallicities and perfect spin transport properties in 2D transition metal dichlorides

Half-metallic band structure and spin transport characteristics of a 1T-FeCl2 monolayer.

Metal adsorption on monolayer blue phosphorene: A first principles study

We investigated the electronic structure, adsorption energies, magnetic properties, dipole moment and work function of metal adatoms (Mg, Cr, Mo, Pd, Pt, and Au) adsorption on a blue phosphorene monolayer. For Mg, Pt and Au metals, the most stable state was found in hollow site while for Cr, Mo and Pd metals we found an adsorption in valley site. We suggest that the Pd and Pt atoms prefer 2D growth mode while the Mg, Cr, Mo and Au atoms prefer 3D island growth mode on monolayer phosphorene. The electronic band structures and magnetic properties were dependent on the doping site and dopant materials. For instance, the semiconducting features were preserved in Mg, Pd, Pt, and Au doped systems. However, the Cr and Mo doped systems displayed half-metallic band structures. The total magnetic moment of 4.05, 2.0 and 0.77 μB/impurity atom were obtained in Cr, Mo and Au doped systems whereas the Mg, Pd and Pt doped systems remained nonmagnetic. We also investigated the magnetic interaction between two transition metal impurities. We observed ferromagnetic coupling between two transition metal impurities in Cr and Mo doped systems while the Au doped system displayed almost degenerated magnetic state. For Mg, Cr, and Mo adsorptions, we found relatively large values of dipole moments compared to those in the Pd, Pt and Au adsorptions. This resulted in a significant suppression of the work function in Mg, Cr and Mo adsorptions. Overall, adsorption can tune the physical and magnetic properties of phosphorene monolayer.

Two-Dimensional Intrinsic Half-Metals With Large Spin Gaps.

Through a systematic search of all layered bulk compounds combined with density functional calculations employing hybrid exchange-correlation functionals, we predict a family of three magnetic two-dimensional (2D) materials with half-metallic band structures. The 2D materials, FeCl2, FeBr2, and FeI2, are all sufficiently stable to be exfoliated from bulk layered compounds. The Fe2+ ions in these materials are in a high-spin octahedral d6 configuration leading to a large magnetic moment of 4 μB. Calculations of the magnetic anisotropy show an easy-plane for the magnetic moment. A classical XY model with nearest neighbor coupling estimates critical temperatures, Tc, for the Berezinskii-Kosterlitz-Thouless transition ranging from 122 K for FeI2 to 210 K for FeBr2. The quantum confinement of these 2D materials results in unusually large spin gaps, ranging from 4.0 eV for FeI2 to 6.4 eV for FeCl2, which should defend against spin current leakage even at small device length scales. Their purely spin-polarized currents and dispersive interlayer interactions should make these materials useful for 2D spin valves and other spintronic applications.