Ab Initio Investigation of the Structural, Elastic, Dynamic, Electronic, and Magnetic Properties of Cubic Perovskite CeCrO3.

We presented the results of various aspects related to structural, elastic, electronic, dynamic, and magnetic parameters of cubic perovskite CeCrO3 by means of the full-potential linearized augmented plane wave (FP-LAPW) approach. The calculation of the unit cell volume against the total energy curve confirms that CeCrO3 exhibits higher energetic stability in the ferromagnetic (FM) order. Calculated structural aspects at equilibrium demonstrate excellent similarity to present information, lending credibility to our results. Moreover, monocrystalline elastic constants have been analyzed numerically. These constants provide insights into several related properties, including elastic anisotropy, mechanical stability, and several polycrystalline elastic aspects. Furthermore, the phonon dispersion curves obtained from our calculations reveal the existence of soft modes, which suggests the potential metastability of CeCrO3. Through an analysis of the energy band dispersions, the half-metallic nature of this material is confirmed, such as Eg = 3.00 and 3.13 eV for the HM state within generalized gradient approximations Perdew-Burke-Ernzerhof (GGA-PBE) and Tran-Blaha modified Becke-Johnson (TB-mBJ) calculations, respectively, as well as the FM total magnetic moment of 4.000 µB. Partial density of states (PDOS) aided in identifying the electronic states that contribute to the energy bands. Finally, the computed total magnetic moment aligns fit the theoretical findings available in the literature.

First-principle investigation of all types of topological nodal lines in a realistic P63/mmc type titanium selenide.

Topological nodal line (TNL) materials with one-dimensional band-crossing points (BCPs) exhibit interesting electronic characteristics and have special applications in electronic devices. Normally, based on the slopes of the crossing bands, the BCPs can be divided into two types, i.e., type I and type II nodal points. Based on the combination of the different types of nodal points, the nodal lines (NLs) can be divided into three categories: (i) type I NL, type II NL, and hybrid NL, these being formed by type I nodal points, type II nodal points, and type I and II nodal points, respectively. Compared with the large number of predicted type I NL materials, there are less type II and hybrid NL materials. In this study, it is predicted that P63/mmc type TiSe metal is a topological material which exhibits all types of NL states. Furthermore, the dynamic stability as well as the effect of spin-orbit coupling on the topological signatures are examined. Also, the nontrivial surface states are shown to provide evidence for the occurrence of the NL states. This novel material can be seen as a good platform to use for further investigations on the three types of NLs and diverse fermions.

Effect of Si, Be, Al, N and S dual doping on arsenene: first-principles insights.

First-principles calculations based on density functional theory (DFT) have been performed to investigate the effect of Si/Be, Si/Al, Si/N and Si/S co-doping on the geometries, electronic structure, magnetism and particularly the adsorption of CO in arsenene. The results show that the incorporation of foreign atoms slightly distorts the host lattice. All doped structures are found to be thermodynamically stable. The replacement of host As atoms with foreign atoms results in some interesting changes in the electronic and magnetic properties of arsenene. The doped arsenene systems exhibit a semiconducting character with band gaps smaller than the original value of 1.59 eV due to the emergence of defect states within the actual band gap. Besides, arsenene remains nonmagnetic (NM) upon Si/Be or Si/S dual doping, whereas both Si/Al and Si/N dopings induce magnetism with a total magnetic moment of 1 µB. Finally, the adsorption of CO molecules over pristine arsenene (p-As) and dual doped arsenene systems is investigated in terms of adsorption energy, adsorption height, charge transfer, charge density difference (CDD), work function, electronic band structures and density of states. It is observed that CO molecule has physisorption over p-As, SiAl-As, SiN-As and SiS-As systems, whereas chemisorption is reported for the SiBe-As system. Our study suggests that chemically modifying arsenene with suitable dopants might extend its applications in spintronic and gas sensing applications.

Phase Transition and Electronic Structures of All-d-Metal Heusler-Type X2MnTi Compounds (X = Pd, Pt, Ag, Au, Cu, and Ni).

In this work, we investigated the phase transition and electronic structures of some newly designed all-d-metal Heusler compounds, X2MnTi (X = Pd, Pt, Ag, Au, Cu, and Ni), by means of the first principles. The competition between the XA and L21 structures of these materials was studied, and we found that X2MnTi favors to feature the L21-type structure, which is consistent with the well-known site-preference rule (SPR). Under the L21 structure, we have studied the most stable magnetic state of these materials, and we found that the ferromagnetic state is the most stable due to its lower energy. Through tetragonal deformation, we found that the L21 structure is no longer the most stable structure, and a more stable tetragonal L10 structure appeared. That is, under the tetragonal strain, the material enjoys a tetragonal phase transformation (i.e., from cubic L21 to tetragonal L10 structure). This mechanism of L21-L10 structure transition is discussed in detail based on the calculated density of states. Moreover, we found that the energy difference between the most stable phases of L10 and L21, defined as ΔE M (ΔE M = E Cubic-E Tetragonal), can be adjusted by the uniform strain. Finally, the phonon spectra of all tetragonal X2MnTi (X = Pd, Pt, Ag, Au, Cu, and Ni) phases are exhibited, which provides a powerful evidence for the stability of the tetragonal L10 state. We hope that our research can provide a theoretical guidance for future experimental investigations.

Perfect Topological Metal CrB2: A One-Dimensional (1D) Nodal Line, a Zero-Dimensional (0D) Triply Degenerate Point, and a Large Linear Energy Range.

Topological materials with band-crossing points exhibit interesting electronic characteristics and have special applications in electronic devices. However, to further facilitate the experimental detection of the signatures of these band crossings, topological materials with a large linear energy range around the band-crossing points need to be found, which is challenging. Here, via first-principle approaches, we report that the previously prepared P6/mmm-type CrB2 material is a topological metal with one pair of 1D band-crossing points, that is, nodal lines, in the kz= 0 plane, and one pair of 0D band-crossing points, that is, triple points, along the A-Γ-A' paths. Remarkably, around these band-crossing points, a large linear energy range (larger than 1 eV) was found and the value was much larger than that found in previously studied materials with a similar linear crossing. The pair of nodal lines showed obvious surface states, which show promise for experimental detection. The effect of the spin-orbit coupling on the band-crossing points was examined and the gaps induced by spin-orbit coupling were found to be up to 69 meV. This material was shown to be phase stable in theory and was synthesized in experiments, and is therefore a potential material for use in investigating nodal lines and triple points.

Insight into the Topological Nodal Line Metal YB2 with Large Linear Energy Range: A First-Principles Study.

The presence of one-dimensional (1D) nodal lines, which are formed by band crossing points along a line in the momentum space of materials, is accompanied by several interesting features. However, in order to facilitate experimental detection of the band crossing point signatures, the materials must possess a large linear energy range around the band crossing points. In this work, we focused on a topological metal, YB2, with phase stability and a P6/mmm space group, and studied the phonon dispersion, electronic structure, and topological nodal line signatures via first principles. The computed results show that YB2 is a metallic material with one pair of closed nodal lines in the kz = 0 plane. Importantly, around the band crossing points, a large linear energy range in excess of 2 eV was observed, which was rarely reported in previous reports that focus on linear-crossing materials. Furthermore, YB2 has the following advantages: (1) An absence of a virtual frequency for phonon dispersion, (2) an obvious nontrivial surface state around the band crossing point, and (3) small spin-orbit coupling-induced gaps for the band crossing points.

Computational Insights Into the Electronic Structure and Magnetic Properties of Rhombohedral Type Half-Metal GdMnO3 With Multiple Dirac-Like Band Crossings.

In spintronics, half-metallic materials (HMMs) with Dirac-like cones exhibit interesting physical properties such as massless Dirac fermions and full spin polarization. We combined first-principles calculations with the quasi-harmonic Debye model, and we proposed that the rhombohedral GdMnO3 is an HMM with multiple linear band crossings. The physical properties of GdMnO3 were studied thoroughly. Moreover, the changes of multiple linear band crossings and 100% spin polarization under spin-orbit coupling as well as the electron and hole doping were also investigated. It is noted that such spin-polarized HMMs with linear band crossings are still very rare in two-dimensional and three-dimensional materials.

Structural configuration and tetragonal phase stability in the equiatomic quaternary Heusler compound TiZnMnSi.

Heusler materials have aroused great scientific research interest during recent years due to their special electronic and magnetic properties. Especially for the equiatomic quaternary Heusler compounds, they exhibit very high composition flexibility and structure tunability. In this work, we have carried out a systematic study on the structural configuration and tetragonal stability for the Heusler compound TiZnMnSi by first-principles calculations. Results reveal the type-A structure with ferromagnetic state possesses the lowest total energy and thus should be the ground state configuration. Based on the equilibrium lattice constant, the electronic band structures and magnetic moments have been computed. The tetragonal phase transformation is then investigated by using the total energy variation under different tetragonal strains, and the stability analysis of the mechanical and dynamic properties indicates that TiZnMnSi exhibits a strong tendency for the tetragonal phase. These findings could provide reference data for relative experiments as well as a very helpful theoretical reference for this fascinating class of materials.

Effect of Zn doping on phase transition and electronic structures of Heusler-type Pd2Cr-based alloys: from normal to all-d-metal Heusler.

Based on first-principles calculations, for Heusler alloys Pd2CrZ (Z = Al, Ga, In, Tl, Si, Sn, P, As, Sb, Bi, Se, Te, Zn), the effect of Zn doping on their phase transition and electronic structure has been studied in this work. These alloys can be divided into two classes: (i) all-d-metal Heusler Pd2CrZn and (ii) other normal Heusler alloys Pd2CrZ (Z = Al, Ga, In, Tl, Si, Sn, P, As, Sb, Bi, Se, Te). For all-d-metal Heusler alloy Pd2CrZn, transition metal element Zn behaves like a main group element due to its full 3d occupied state, and therefore the Zn atoms tend to occupy Wyckoff sites D (0.75, 0.75, 0.75) instead of replacing Pd atoms at A sites (0, 0, 0). The stable tetragonal L10 state is obtained via tetragonal deformation and the L10 stable state can be tuned by the uniform strain. The stability of the tetragonal state is analyzed and proved via calculation of the density of states (DOSs) and the phonon spectrum. For the series of normal Heusler alloys Pd2CrZ, doping with Zn atoms can induce or strengthen the martensitic transformation, or regulate the large c/a ratios to a more reasonable range. It is hoped that this work can provide some guidance for further studies of the relationship between all-d-metal and normal Heusler alloys in the future.

R3c-type LnNiO3 (Ln = La, Ce, Nd, Pm, Gd, Tb, Dy, Ho, Er, Lu) half-metals with multiple Dirac cones: a potential class of advanced spintronic materials.

In the past three years, Dirac half-metals (DHMs) have attracted considerable attention and become a high-profile topic in spintronics becuase of their excellent physical properties such as 100% spin polarization and massless Dirac fermions. Two-dimensional DHMs proposed recently have not yet been experimentally synthesized and thus remain theoretical. As a result, their characteristics cannot be experimentally confirmed. In addition, many theoretically predicted Dirac materials have only a single cone, resulting in a nonlinear electromagnetic response with insufficient intensity and inadequate transport carrier efficiency near the Fermi level. Therefore, after several attempts, we have focused on a novel class of DHMs with multiple Dirac crossings to address the above limitations. In particular, we direct our attention to three-dimensional bulk materials. In this study, the discovery via first principles of an experimentally synthesized DHM LaNiO3 with many Dirac cones and complete spin polarization near the Fermi level is reported. It is also shown that the crystal structures of these materials are strongly correlated with their physical properties. The results indicate that many rhombohedral materials with the general formula LnNiO3 (Ln = La, Ce, Nd, Pm, Gd, Tb, Dy, Ho, Er, Lu) in the space group R 3 c are potential DHMs with multiple Dirac cones.

Investigation of the structural competing and atomic ordering in Heusler compounds Fe2NiSi and Ni2FeSi under strain condition.

The structural competing and atomic ordering of the full Heusler compounds Fe2NiSi and Ni2FeSi under uniform and tetragonal strains have been systematically studied by the first-principles calculation. Both Fe2NiSi and Ni2FeSi have the XA structure in cubic phase and they show metallic band structures and large magnetic moments (greater than 3µ B ) at equilibrium condition. Tetragonal distortion can further decrease the total energy, leading to the possible phase transformation. Furthermore, different atom reordering behaviours have been observed: for Fe2NiSi, atoms reorder from cubic XA-type to tetragonal L10-type; for Ni2FeSi, there is only structural transformation without atom reordering. The total magnetic moments of Fe2NiSi and Ni2FeSi are mainly contributed by Fe atoms, and Si atom can strongly suppress the moments of Fe atoms when it is present in the nearest neighbours of Fe atoms. With the applied strain, the distance between Fe and Si atoms play an important role for the magnetic moment variation of Fe atom. Moreover, the metallic band nature is maintained for Fe2NiSi and Ni2FeSi under both uniform and tetragonal strains. This study provides a detailed theoretical analysis about the full Heusler compounds Fe2NiSi and Ni2FeSi under strain conditions.

Palladium (III) Fluoride Bulk and PdF3/Ga2O3/PdF3 Magnetic Tunnel Junction: Multiple Spin-Gapless Semiconducting, Perfect Spin Filtering, and High Tunnel Magnetoresistance.

Spin-gapless semiconductors (SGSs) with Dirac-like band crossings may exhibit massless fermions and dissipationless transport properties. In this study, by applying the density functional theory, novel multiple linear-type spin-gapless semiconducting band structures were found in a synthesized R 3 - c -type bulk PdF3 compound, which has potential applications in ultra-fast and ultra-low power spintronic devices. The effects of spin-orbit coupling and on-site Coulomb interaction were determined for the bulk material in this study. To explore the potential applications in spintronic devices, we also performed first-principles combined with the non-equilibrium Green's function for the PdF3/Ga2O3/PdF3 magnetic tunnel junction (MTJ). The results suggested that this MTJ exhibits perfect spin filtering and high tunnel magnetoresistance (~5.04 × 107).

Robust Spin-Gapless Behavior in the Newly Discovered Half Heusler Compound MnPK.

Spin gapless semiconductors have aroused high research interest since their discovery and a lot of effort has been exerted on their exploration, in terms of both theoretical calculation and experimental verification. Among different spin gapless materials, Heusler compounds stand out thanks to their high Curie temperature and highly diverse compositions. Especially, both theoretical and experimental studies have reported the presence of spin gapless properties in this kind of material. Recently, a new class of d0 - d Dirac half Heusler compound was introduced by Davatolhagh et al. and Dirac, and spin gapless semiconductivity has been successfully predicted in MnPK. To further expand the research in this direction, we conducted a systematical investigation on the spin gapless behavior of MnPK with both generalized gradient approximation (GGA) and GGA + Hubbard U methods under both uniform and tetragonal strain conditions by first principles calculation. Results show the spin gapless behavior in this material as revealed previously. Different Hubbard U values have been considered and they mainly affect the band structure in the spin-down channel while the spin gapless feature in the spin-up direction is maintained. The obtained lattice constant is very well consistent with a previous study. More importantly, it is found that the spin gapless property of MnPK shows good resistance for both uniform and tetragonal strains, and this robustness is very rare in the reported studies and can be extremely interesting and practical for the final end application. This study elaborates the electronic and magnetic properties of the half Heusler compound MnPK under uniform and tetragonal strain conditions, and the obtained results can give a very valuable reference for related research works, or even further motivate the experimental synthesis of the relative material.

Competition between cubic and tetragonal phases in all-d-metal Heusler alloys, X 2-x Mn1+x V (X = Pd, Ni, Pt, Ag, Au, Ir, Co; x = 1, 0): a new potential direction of the Heusler family.

In this work, a series of all-d-metal Heusler alloys, X 2 - x Mn1 + x V (X = Pd, Ni, Pt, Ag, Au, Ir, Co; x; = 1, 0), were predicted by first principles. The series can be roughly divided into two categories: XMn2V (Mn-rich type) and X 2MnV (Mn-poor type). Using optimized structural analysis, it is shown that the ground state of these all-d-metal Heusler alloys does not fully meet the site-preference rule for classic full-Heusler alloys. All the Mn-rich type alloys tend to form the L21 structure, where the two Mn atoms prefer to occupy the A (0, 0, 0) and C (0.5, 0.5, 0.5) Wyckoff sites, whereas for the Mn-poor-type alloys, some are stable with XA structures and some are not. The c/a ratio was also changed while maintaining the volume the same as in the cubic state to investigate the possible tetragonal transformation of these alloys. The Mn-rich Heusler alloys have strong cubic resistance; however, all the Mn-poor alloys prefer to have a tetragonal state instead of a cubic phase through tetragonal transformations. The origin of the tetragonal state and the competition between the cubic and tetragonal phases in Mn-poor alloys are discussed in detail. Results show that broader and shallower density-of-states structures at or in the vicinity of the Fermi level lower the total energy and stabilize the tetragonal phases of X 2MnV (X = Pd, Ni, Pt, Ag, Au, Ir, Co). Furthermore, the lack of virtual frequency in the phonon spectra confirms the stability of the tetragonal states of these Mn-poor all-d-metal Heusler alloys. This work provides relevant experimental guidance in the search for possible martensitic Heusler alloys in all-d-metal materials with less Mn and new spintronic and magnetic intelligent materials among all-d-metal Heusler alloys.

The electronic, half-metallic, and magnetic properties of Ca1-xCrxS ternary alloys: Insights from the first-principle calculations.

The electronic, structural, and magnetic characteristics of Cr atom substituting Ca atom in rocksalt CaS have been investigated within the formalism of (GGA + PBE) and PBE with Hubbard correction (GGA + U). Our findings point out that the ternary alloys are dynamically stable depending on the obtained results of elastic constants. For structural properties, it is clear that the lattice constants decrease and bulk modulus increases with increasing concentration of chromium impurity. Interestingly, the perceived total magnetic moments increase with the Cr concentration and reaches the maximum for Ca0.25Cr0.75S, which is mainly composed of Cr atoms. Besides, it is found from PBE and PBE + U calculations that the Cr-substituted CaS gives half-metallic ferromagnetism (HMF). Finally, the deduced results of minority-spin bands demonstrate a half-metallic ferromagnetic gap and half-metallic (HM) gap. The predicted results confirmed that Ca1-xCrxS could be considered as a promising candidate material for spintronics applications.

Lattice dynamics, mechanical stability and electronic structure of Fe-based Heusler semiconductors.

The structural and mechanical stability of Fe2TaAl and Fe2TaGa alloys along with the electronic properties are explored with the help of density functional theory. On applying different approximations, the enhancement of semiconducting gap follows the trend as GGA < mBJ < GGA + U. The maximum forbidden gaps observed by GGA + U method are Eg = 1.80 eV for Fe2TaAl and 1.30 eV for Fe2TaGa. The elastic parameters are simulated to determine the strength and ductile nature of these materials. The phonon calculations determine the dynamical stability of all these materials because of the absence of any negative frequencies. Basic understandings of structural, elastic, mechanical and phonon properties of these alloys are studied first time in this report.

Structural, Elastic, Electronic and Optical Properties of SrTMO3 (TM = Rh, Zr) Compounds: Insights from FP-LAPW Study.

The structural, mechanical, electronic and optical properties of SrTMO3 (TM = Rh, Zr) compounds are investigated by using first principle calculations based on density functional theory (DFT). The exchange-correlation potential was treated with the generalized gradient approximation (GGA) for the structural properties. Moreover, the modified Becke-Johnson (mBJ) approximation was also employed for the electronic properties. The calculated lattice constants are in good agreement with the available experimental and theoretical results. The elastic constants and their derived moduli reveal that SrRhO3 is ductile and SrZrO3 is brittle in nature. The band structure and the density of states calculations with mBJ-GGA predict a metallic nature for SrRhO3 and an insulating behavior for SrZrO3. The optical properties reveal that both SrRhO3 and SrZrO3 are suitable as wave reflectance compounds in the whole spectrum for SrRhO3 and in the far ultraviolet region (FUV) for SrZrO3.

Strain Conditions for the Inverse Heusler Type Fully Compensated Spin-Gapless Semiconductor Ti2MnAl: A First-Principles Study.

In this work, we systematically studied the structural, electronic, magnetic, mechanical and thermodynamic properties of the fully compensated spin-gapless inverse Heusler Ti2MnAl compound under pressure strain condition by applying the first-principles calculation based on density functional theory and the quasi-harmonic Debye model. The obtained structural, electronic and magnetic behaviors without pressure are well consistent with previous studies. It is found that the spin-gapless characteristic is destroyed at 20 GPa and then restored with further increase in pressure. While, the fully compensated ferromagnetism shows a better resistance against the pressure up to 30 GPa and then becomes to non-magnetism at higher pressure. Tetragonal distortion has also been investigated and it is found the spin-gapless property is only destroyed when c/a is less than 1 at 95% volume. Three independent elastic constants and various moduli have been calculated and they all show increasing tendency with pressure increase. Additionally, the pressure effects on the thermodynamic properties under different temperature have been studied, including the normalized volume, thermal expansion coefficient, heat capacity at constant volume, Grüneisen constant and Debye temperature. Overall, this theoretical study presents a detailed analysis of the physical properties' variation under strain condition from different aspects on Ti2MnAl and, thus, can provide a helpful reference for the future work and even inspire some new studies and lead to some insight on the application of this material.

New Half-Metallic Materials: FeRuCrP and FeRhCrP Quaternary Heusler Compounds.

The electronic structures and magnetic properties of FeRuCrP and FeRhCrP quaternary Heusler compounds with LiMgPbSb-type structures have been investigated via first-principles calculations. The calculational results show that both FeRuCrP and FeRhCrP compounds present perfect half-metallic properties: Showing large half-metallic band gaps of 0.39 eV and 0.38 eV, respectively. The total magnetic moments of FeRuCrP and FeRhCrP are 3 µB and 4 µB per formula unit, respectively. The magnetism of them mainly comes from the 3d electrons of Cr atoms and follows the Slater-Paulig behavior of Heusler compounds: Mt = Zt - 24. Furthermore, the half-metallic properties of FeRuCrP and FeRhCrP compounds can be kept in a quite large range of lattice constants (about 5.44-5.82 Å and 5.26-5.86 Å, respectively) and are quite robust against tetragonal deformation (c/a ratio in the range of 0.94-1.1 and 0.97-1.1, respectively). Moreover, the large negative cohesion energy and formation energy of FeRuCrP and FeRhCrP compounds indicate that they can be synthesized experimentally.

Rare earth-based quaternary Heusler compounds MCoVZ (M = Lu, Y; Z = Si, Ge) with tunable band characteristics for potential spintronic applications.

Magnetic Heusler compounds (MHCs) have recently attracted great attention since these types of material provide novel functionalities in spintronic and magneto-electronic devices. Among the MHCs, some compounds have been predicted to be spin-filter semiconductors [also called magnetic semiconductors (MSs)], spin-gapless semiconductors (SGSs) or half-metals (HMs). In this work, by means of first-principles calculations, it is demonstrated that rare earth-based equiatomic quaternary Heusler (EQH) compounds with the formula MCoVZ (M = Lu, Y; Z = Si, Ge) are new spin-filter semiconductors with total magnetic moments of 3 µB. Furthermore, under uniform strain, there are physical transitions from spin-filter semiconductor (MS) → SGS → HM for EQH compounds with the formula LuCoVZ, and from HM → SGS → MS → SGS → HM for EQH compounds with the formula YCoVZ. Remarkably, for YCoVZ EQH compounds there are not only diverse physical transitions, but also different types of spin-gapless feature that can be observed with changing lattice constants. The structural stability of these four EQH compounds is also examined from the points of view of formation energy, cohesive energy and mechanical behaviour. This work is likely to inspire consideration of rare earth-based EQH compounds for application in future spintronic and magneto-electronic devices.