Half-metallic Character Research Articles

Theoretical Prediction of Structural Stability, Electronic, Elastic, and Magnetic Properties of the New Half Metallic Half-Heusler XSrC (X=Li and Na) Alloys

In this paper, structural, elastic, electronic and magnetic properties of half-Heusler XSrC ([Formula: see text] and Na) compounds have been investigated utilizing full potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). For exchange-correlation potentials, the generalized gradient approximation (GGA) has been used. The calculated cohesive and formation energy values showed that these compounds can be experimentally synthesized. The elastic properties were analyzed in detail and reveal that LiSrC and NaSrC compounds are mechanically stable. The spin-polarized band structure and density of states illustrate that LisrC and NaSrC alloys have a half metallic character. The total magnetic moment is 1[Formula: see text][Formula: see text] per formula unit that confirms the half metallic behavior and follows the Slater-Pauling rule [Formula: see text]. For half-Heusler XSrC ([Formula: see text] and Na) compounds, there are no available experimental or theoretical studies, our calculations are considered as first predictions.

First-principles study to probe the effect of substitution at X and Z sites on the electronic, magnetic and transport properties of Co2X(V, Nb, Ta)Z(Al, Ga, In, Si, Ge, Sn) Heusler alloys

In the present work, we have used density functional theory based electronic structure calculations to probe the role of isovalent substitution at X@(0.5, 0.5, 0.5) and Z@(0, 0, 0) site of Co2X(= Ta, Nb, V)Z(= Al, Ga, In). Further, we probed the role of electron-rich substitution at Z site on the electronic, magnetic and transport properties of half-metallic(HM) Co2TaZ( = Al,Ga,In) full Heusler alloys(FHA). One of our main aims is to study the effect of electron-rich substitution at Z site on the total and partial moments of X and Z sites. We have used the modified Becke–Johnson(mBJ) exchange–correlation term to calculate the HM band-gap. We observe that, isovalent substitution at X and Z sites provides a way to tune the lattice constant in range of ∼5.75 Å to ∼6.16 Å with sustained HM character. Further, it is noticed that the HM band-gap decreases with isovalent substitution (with low atomic number) at X site with maximum and minimum values of 1.09 eV and 0.5 eV, respectively. Isovalent substitution does not affect the total magnetic moment, however, it affects the atomic magnetic moment values. Further, we observe that 25% of substitution of tetravalent atoms (Si, Ge, Sn) at atomic site Z (having Al, Ga, In) enhances the total magnetic moment with a small decrease in the minority band-gap. However, 75 to 100 % of substitutions destroy the half-metallicity, showing an enhancement in the magnetic moment. Temperature dependent spin Seebeck coefficients corresponding to the 25% and 75% of substitution of tetravalent element at Z site exhibit values close to 150 μV/K and 25–75 μV/K, respectively, for temperatures above 400 K. Interestingly, electron rich substitution at Z cite, changes the orientation of the magnetic moment corresponding to the X (Ta) site element. In order to understand in detail the impact of substitution on the local magnetic moment of Co and X site atoms (V, Nb, Ta), we have performed calculations of respective X-ray magnetic circular dichroism(XMCD) spectra and analyzed the results in terms of unoccupied density of states. XMCD spectra of L2,3 edges of Co atom show only small deviation (in the intensity) with the changes in the X and Z sites. Unlike the case of Co atom, we find that the XMCD spectra of M2,3 edges of Ta atom exhibit substantial changes when tetravalent atoms replace the trivalent atoms at the Z site.

Scrutinized the inherent spin half-metallicity and thermoelectric response of f-electron-based RbMO3 (M = Np, Pu) perovskites: a computational assessment

In the hunt for novel materials, we present self-consistent ab initio simulations of the structural stability, electronic profile, and transport properties of f-electron-based RbMO3 (M = Np, Pu) perovskites within the context of density functional theory. The structural stability and thermodynamic concerns are fixed by relaxing the crystal structure and computing the energy of formation, respectively. Furthermore, the decisive physical features of given materials have been outlined using the optimised lattice constant retrieved from structural optimizations. The ground state magnetic phase stability is ascertained by minimizing Birch Murnaghan's equation of state in distinct magnetic phases, upholding the ferromagnetic phase (FM) as the ground state magnetic phase, which is further backed by positive Curie Wiess constant values. To specify the electronic structure, a mix of the two approximations GGA and GGA + mBJ has been executed, both of which assert the half-metallic character, culminating in 100% spin polarisation at the Fermi level. The study of the magnetic moment and Curie temperature of each material has further been assessed in the present study. Apart from half-metallicity, the thermoelectric response of the present materials is quantified by exploring the chemical potential dependency of several transport parameters like Seebeck coefficient, electrical and thermal conductivity, power factor, etc. Moreover, the thermoelectric competence has been tested using a zT calculation, adapting values of 1.01 and 0.987 at 300 K for RbNpO3 and RbPuO3, respectively. The high electronic zT at encompassing temperatures uncovers the significant utility of these materials in both low-and high-temperature thermoelectric device applications. In essence, the comprehensive survey of these alloys could certainly open up their possibilities in spintronics, thermoelectric, and solid-state (RTG) device applications.

Phase stability and half-metallic character of off-stoichiometric Co2FeGa0.5Ge0.5 Heusler alloys

We investigate the effects of off-stoichiometric compositional variations from the Co2Fe(Ga0.5Ge0.5) (CFGG) full-Heusler alloy on its half-metallic electronic structure. First-principles calculations predict that the Co antisite defects that occupy Fe-sites (CoFe) lead to a finite DOS in the half-metallic gap of CFGG. Fe antisites defects in Co-sites (FeCo) introduced by excessing Fe composition, which could suppress the formation of CoFe, preserves the half-metallic gap but reduces spin polarization because the Fermi level shifts to the lower energy. We found that, in Fe-excess CFGG, Ge-excess has an important role to enhance the spin polarization by lifting up the Fermi level position and suppressing the formation of CoFe. To confirm the effect of the Fe and Ge-excess off-stoichiometric composition on spin polarization and phase-purity experimentally, we fabricated CFGG epitaxial thin films with various composition ratios (Co2−αFe1+α) (Ga1−βGeβ)1+γ with small positive γ (=0.09–0.29). It turns out that Co1.75Ge or Fe1.7Ge secondary phase often forms in the films for β≥0.69 in Fe-deficient (α≤0.21) and excess (α≥0.49) compositions. This secondary phase can be suppressed by tuning the Ge and Fe compositions, and the L21-phase pure film was found in Co39.4Fe29.3Ga13.4Ge17.9 (α=0.28,β=0.57,γ=0.25). The measurements of conventional magnetoresistance effects qualitatively indicate higher spin polarization in the Co39.4Fe29.3Ga13.4Ge17.9 film compared to other Co-excess and Ge-deficient films, which evidences the benefit to make Fe- and Ge-excess off-stoichiometric CFGG for obtaining the half-metallic nature of CFGG.

The Structural, Electronic, Magnetic and Elastic Properties of Full-Heusler Co2CrAl and Cr2MnSb: An Ab Initio Study

In this paper, the full-potential, linearized augmented plane wave (FP-LAPW) method was employed in investigating full-Heusler Co2CrA1’s structural, elastic, magnetic and electronic properties. The FP-LAPW method was employed in computing the structural parameters (bulk modulus, lattice parameters, c/a and first pressure derivatives). The optimized structural parameters were determined by generalized gradient approximation (GGA) for the exchange-correlation potential, Vxc. Estimating the energy gaps for these compounds was accomplished through modified Becke–Johnson potential (mBJ). It was found that the conventional Heusler compound Co2CrA1 with mBJ and CGA approaches had a half-metallic character, and its spin-down configuration had an energy gap. It was also found that the conventional and inverse Heusler Cr2MnSb and tetragonal (139) (Co2CrA1, Cr2MnSb) compounds with a half-metallic character had direct energy gaps in the spin-down configuration. To a certain degree, the total magnetic moments for the two compounds were compatible with the theoretical and experimental results already attained. Mechanically, we found that the conventional and inverse full-Heusler compound Co2CrAl was stable, but the inverse Cr2MnSb was unstable in the ferromagnetic state. The conventional Heusler compound Cr2MnSb was mechanically stable in the ferromagnetic state.

Effect of 4d transition metals on the electronic and magnetic properties of twin graphene

To explore new uses for twin graphene (TG) in spintronic devices, we tuned the electronic properties and introduced a magnetic moment for TG by doping it with 4d transition metal (TM = Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, and Cd) atoms. Some single TM doped TG systems have spin-polarized states, and their magnetic moments can be divided into three categories. TG doped with single Y, Mo, and Ag exhibits dilute magnetic semiconductor (DMS) properties, and the doping of Tc introduces a half-metallic character. For dual-doped systems, the electronic properties of TG can be effectively regulated by the doping positions of various TM atoms. The α-2Mo/TG, α-2Tc/TG, β-2Y/TG, and γ-2Y/TG systems exhibit DMS behavior. Some dual-doped systems exhibit antiferromagnetic (AFM) and ferromagnetic (FM) behaviors. For β configurations, the electronic properties of TM atoms dual-doped on the same and different sides of TG are similar to those of the corresponding single-doped systems, except for the β/D-2Zr/TG and β/D-2Ag/TG systems. The dual-doping of Y and Rh atoms on the same and different sides of TG can realize the switch between AFM and FM. The results of this study might provide new inspiration for applying TG in spintronic and nanomagnet devices.

Effect of B substitution for Si on the electronic structure and magnetic properties of Heusler alloys Fe2CoSi1-xBx (x = 0–0.25)

A series of Fe2CoSi1-xBx (x = 0, 0.05, 0.1, 0.15, 0.2 and 0.25) Heusler alloys has been synthesized using melt-spinning method, which can help to reduce the precipitation of the secondary phase and form a highly ordered structure. The XRD patterns indicate that, when x = 0–0.1 the Fe2CoSi1-xBx melt-spun ribbons are single Heusler phases, but when x = 0.2 and 0.25 a small amount of secondary phase appears. The lattice constant decreases with increasing B content, suggesting that B mainly enters the substitutional sites of Si. The Curie temperatures TC of Fe2CoSi1-xBx alloys are all higher than 1000 K, and a 21 K increase of TC is observed as x varies from 0 to 0.25. The hysteresis loops of Fe2CoSi1-xBx alloys show soft magnetic character. Their saturation magnetizations Ms at 5 K and 300 K are similar and close to 5μB / f.u. The zero-gap half-metallic character reported for Fe2CoSi has been confirmed in present work. But with the substitution of B for Si, the Fermi level moves from the center in Fe2CoSi DOS to the left edge of the minority energy gap in Fe2CoSi0.75B0.25, which may disturb the half-metallic character when B content is high. When × = 0–0.1, the Ms at 5 K of Fe2CoSi1-xBx agree well with the calculated total spin moments, but when the B content is high, especially when x = 0.2 and 0.25, a deviation between the experimental and theoretical results is observed, which is related to the secondary phase in these samples.

Ab initio prediction of half-metallicity in the NaMnZ2 (Z = S, Se, Te) ternary layered compounds

Motivated by recent theoretical studies predicting half-metallicity in some ternary manganese chalcogenides, first-principles calculations based on spin-polarized density functional theory (DFT) are applied to investigate the structural, elastic, electronic and magnetic properties of the ternary layered compounds NaMnZ2 (Z = S, Se, Te). We assume for all compounds the experimentally determined, in the case of NaMnSe2 and NaMnTe2 compounds, noncentrosymmetric trigonal structure (space group P3m1; no. 156). The analysis of spin-polarized band structures and of the diagrams of density of states reveals the half-metallic character of the considered materials. We find that the strong spin polarization of the d orbitals of the manganese atoms is at the origin of the ferromagnetism of these compounds with a total magnetic moment per formula unit of 4μB. The studied compounds show a Slater-Pauling behavior and the total spin magnetic moment per cell (Mt) evolves with the total number of valence electrons (Zt) according to the lawMt=(Zt−22)μB. The calculated values of the minority-spin energy gap (Eg) and of the half-metallic gap (EHM) for the explored materials show that they are promising compounds for spintronic applications.

Tuning the electrocatalytic CO reduction on bilayer C3N via rotation, translation and metal intercalation

Owing to the crucial role of the CO reduction in the sustainable development and carbon neutrality, designing tunable electrocatalyst with high efficiency is the top priority for the controllable CO reduction reaction (CORR). Inspired by the interlayer van der Waals coupling modification, we have theoretically explored the tunable catalyst for the CO electrochemical reduction based on the bilayer C3N (b-C3N) via the rotation, translation and transition metal intercalation. Through careful computational screening, we found that rotational and/or translational intermodulation to the transitional metal intercalated b-C3N (TM/b-C3N) can tune its catalytic activity and selectivity efficiently and therefore control the reaction rates and final product distribution. The electronic analysis revealed the half-metallic characteristic of the TM intercalated b-C3N and found that the electrons transferring from the intercalated metal to the adsorbed molecules with the rotated (or translated) b-C3N acting as transferring bridge can further activate the catalyst surface. This study provides a new strategy to design novel CORR catalyst with tunable catalytic activities by mechanical operations, such as rotation, translation and intercalation, and will open a new door for the application of controllable COx reduction.

Stabilities and half-metallic ferromagnets features of new quaternary Heusler alloys RhCoVX (X = Si, Ge and Sn). Ab-initio study

New quaternary Heusler alloys (QHAs) RhCoVX (X = Si, Ge, and Sn) were investigated for stability and half-metallic ferromagnet features. Three nonequivalent structural arrangements of type I, II, and III structures are considered. Type I is described as the most stable phase for all these compounds in ferromagnetic order compared to non-magnetic order. We also demonstrate the thermodynamic, dynamic, and mechanical stability of RhCoVX (X = Si, Ge, and Sn) by computing the cohesive energies, formation energies, phonon dispersion curves, and elastic constants. Using GGA-mBJ and LDA-mBJ calculations show that RhCoVX (X = Si, Ge, and Sn) are half-metallic ferromagnets (HMFs), with indirect bandgap through the altered Becke-Johnson (mBJ), in the two approach's LDA-mBJ and GGA-mBJ: 1.03 eV (0.922 eV) for RhCoVSi, 0.956 eV (0.856 eV) for RhCoVGe and 0.706 eV (0.662 eV) for RhCoVSn. Furthermore, the electrons at the Fermi level (EF) were fully spin-polarized. The total magnetic moment in these three compounds was found as an integer value of 3.00 μB per formula, which complies with the Slater-Pauling rule Mt = Zt - 24. According to the given results, these compounds are promising materials for spintronic applications. All calculations used the density functional theory (DFT) based on the full-potential linearized augmented plane wave (FP-LAPW) method implemented in the WIEN2K code.

Possible half-metallicity and suppressed double-exchange interaction in spinel Mn2.4Ni0.6O4: A Ni-substitution effect

In this work, we present detailed structural, magnetic, dielectric, and transport properties as well as electronic structure studies of a Mn2.4Ni0.6O4 system. The Mn2.4Ni0.6O4 system acquires cubic Fd3̅m crystal structure at room temperature and exhibits a ferrimagnetic transition around 108 K. The pristine Mn3O4 acquires a tetragonal I41/amd structure at room temperature and exhibits ferrimagnetic transition and magneto-dielectric coupling at around 43 K. The magneto-dielectric coupling is found to be absent in cubic Mn2.4Ni0.6O4, but still shows interesting transport behavior. The resistivity results show semiconducting behavior of the system, but interestingly, this semiconducting behavior weakens at low temperatures. This is evident from the decreased rate of change of resistivity with decreasing temperature. X-ray absorption spectra results have confirmed that to compensate for the charge imbalance caused by Ni2+ cations at the octahedral-site, a few Mn3+ cations transform into Mn4+. The density of state calculations reveal that at Fermi-level, Mn2.4Ni0.6O4 exhibits small but finite bands in the majority channel while a band gap of 1.5 eV exists in the minority channel. The ground state electronic structure of Mn2.4Ni0.6O4 predicts a half-metallic character for the system. The partial density of states analysis of Mn2.4Ni0.6O4 suggests that the bands near the Fermi-level are predominantly contributions of Mn3+, Mn4+ and O2-. We further discuss the origin of the weak semiconducting behavior of Mn2.4Ni0.6O4 at low temperatures.

First principles investigations of optoelectronic and magnetic properties of co-doped zinc sulphide by 3d and 4f elements

In this work, optoelectronic and magnetic properties of Co-doped and (Co, Sm) co-doped ZnS have been studied using the first principles calculation based on density functional theory (DFT) and FP-LAPW method with GGA and GGA + U approximations in zinc blende structure. The lattice parameter will increase by (Co, Sm) co-doping ZnS. The difference in total energy is calculated and confirms the stability of ZnS: Co in ferromagnetic states (FM) and ZnS: (Co, Sm) in antiferromagnetic states (AFM). The total magnetic moment is found to be more interesting by (Co, Sm) co-doping. The band structure, the total density of states (TDOS) and partial density of states (PDOS) show that ZnS: Co has a semiconducting character. While ZnS: (Co, Sm) has half-metallic character behavior with 100% spin polarization at the Fermi level provided by the RE-4f states. Moreover, optical properties such as dielectric functions and absorption coefficients for ZnS: Co and ZnS: (Co, Sm) were also discussed and found to be more interesting in the visible region by (Co, Sm) co-doping. The improved optical and magnetic results indicate that (Co, Sm) co-doped ZnS can be used as a promising candidate for optoelectronic and spintronic devices in the future.

Effects of atomic displacements on band gaps of Na2MgXO6 (X= Co, Fe) double perovskite oxides: GGA and GGA+U approaches

True half-metallic materials are among the most preferred material groups in spintronic applications with their 100% spin polarization. Perovskite materials have formed the basis of many semiconductor devices in recent years with their widespread technological use. In this study, Na2MgXO6 (X = Co, Fe) perovskite oxides were obtained as true half-metallic materials, and the effects of the atomic displacements between Mg and Co/Fe atoms on electronic, magnetic and half-metallic characters were investigated. First, volume-energy optimization curves were calculated, and ferromagnetic phases were energetically more stable. Second, electronic calculations were performed, and semiconducting band gaps were seen in the up-spin states. The band gaps of Na2MgCoO6 and Na2CoMgO6 oxides were obtained as 0.531 eV and 1.1446 eV, respectively. Then atomic displacements between Mg and Co/Fe-transition metals happened and band gaps of Na2MgFeO6 and Na2FeMgO6 oxides were obtained as 0.487 eV and 2.142 eV, respectively. As can be seen, the atomic structure changes directly affected the band gaps. Additionally, GGA + U interactions were performed for electronic calculations. As a result of increasing U-interactions, band gaps decreased. It is possible to say that all band gaps change with the effect of atomic compositions. Finally, the total magnetic moments of Na2MgCoO6 and Na2MgFeO6 oxides were obtained as 5.00 μB/f.u. and 6.00 μB/f.u., respectively. Na2MgXO6 (X = Co, Fe) oxides with half-metallic ferromagnetic features and high magnetic moment values are very useful materials for spintronic applications.

Electronic structure and magnetism of pristine, defected, and strained Ti2N MXene

From first principles electronic structure calculations, we unravel the evolution of structural, electronic, and magnetic properties of pristine, defected, and strained titanium nitride MXene with different functional groups (-F, -O, -H, and -OH). The formation and cohesive energies reveal their chemical stability. The dynamical stability of Ti2N mono-layer is also confirmed by phonon calculations. The MAX phase and defect free functionalized MXenes are metallic except for oxygen terminated (Ti2NO2) one which is 100% spin polarized half-metallic ferromagnet. The spin–orbit coupling significantly influences the bare MXene (Ti2N) to exhibit Dirac topology and band inversion near the high symmetry directions. The strain effect sways the Fermi level thereby shifting it towards lower energy state under compression and towards higher energy state under tensile strain in Ti2NH2. The Ti2NO2 exhibits exotic electronic structure not only in pristine but also in strained and defected structures. Its half-metallic nature changes to semi-metallic under 1% compression and it is completely destroyed under 2% compression. In single vacancy defect, its band structure remarkably transforms from half-metallic to semi-conducting with large band gap in 12.5% Ti, weakly semi-conducting in 5.5% Ti, and semi-metallic in 12.5% O. The 25% N defect changes its half-metallic characteristic to metallic. Further, the 12.5% Co substitution preserves its half-metallic character, whereas Mn substitution allows it to convert half-metallic characteristic into weak semi-metallic characteristic preserving ferromagnetism. However, Cr substitution converts half-metallic ferromagnetic state to half-metallic anti-ferromagnetic state. The understanding made here on collective structural stability, and electronic band structure, and magnetic phenomena in novel 2D Ti2N derived MXenes open up their possibility in designing them for synthesis.

A promising robust intrinsic half-metallic MXene nanosheet Cr2CuC2 with high Curie temperature

Two-dimension half-metallic ferromagnets are promising in spintronics. In recent years, the half-metallicity and the magnetic properties of the MXene materials have been research hotspots of new materials due to their unique crystal characteristics and wide promising applications. A new promising robust intrinsic half-metallic MXene nanosheet Cr2CuC2 with high Curie temperature (evidently above the room temperature) was predicted from the first principles calculations. The magnetic moment of this nanosheet is calculated as 5.00 μB per unit. Its half-metallic character and the magnetic moment mainly origin from the spin-polarized Cr-ions induced by the crystal field. With increase of the biaxial tensile strain on this nanosheet, its magnetic moment per unit remains 5.00 μB well. More importantly, its energy gap of the spin-down subband and the half-metallic energy gap both increase with the tensile strain, implying that the half-metallicity of this nanosheet may be evidently improved by the biaxial tensile strain. Charge state may cause important influence on the magnetic and electric properties of this nanosheet. If an electron is removed from this nanosheet, its magnetic moment per unit decreases from 5.00 μB to 4.00 μB, while its half-metallic character remains well. These magnetic moments per unit of this nanosheet before/after an electron is removed accord well to those analyzed by the two-center molecular orbital theory.

Electronic Behavior and Optical Properties of New Ferromagnetic Silver-Based Sulfo-spinel: AgV2S4

This study reports the intriguing properties of a novel ternary silver-based sulfo-spinel vanadium system (AgV2S4) having a face centered cubic structure (FCC). The magnetic nature, electronic behavior and optical properties of this system are revealed. The calculations were performed with spin-effect and by using generalized gradient approximation (GGA) under Density Functional Theory (DFT). After obtaining the optimized Wyckoff positions for the atoms in the crystal structure of this composition, it was decided that this spinel material has ferromagnetic nature in view of the energy-volume curves obtained for three different magnetic phases and of the calculated cohesive energies. Furthermore, the spin-polarized electronic band structure with the orbital projected density of electronic states was calculated within first principles to investigate its electronic behavior and bonding characteristic in detail. The observed small band gap in minority spin channel is Eg = 0.41 eV, so its electronic band structure imply that this system has half-metallic character. Finally, to evaluate some optical features, frequency dependent complex dielectric functions were calculated. Then, some optical properties were investigated by using the real and imaginary parts of the dielectric function.

B2-disorder effects on the structural, electronic and magnetic properties of Co2MnAl Heusler alloy

Co-based Heusler alloys are mostly studied for their half metallicity, resulting in 100% spin polarization and a very high Curie temperature, which are the prerequisites for spintronics devices. As the site (swap) disorder has a significant impact on these properties, understanding of the impact of site disorder on these properties is of great interest for the spintronic community. First principle calculations within density functional theory (DFT) have been carried out on the structural, electronic, and magnetic properties of the B2 disordered Co2MnAl full Heusler alloy along with that of L21 ordered structure for comparison purpose. The plane wave pseudopotential method, within the Generalized Gradient approximation for exchange correlation functional was used to study B2 disordered Co2MnAl Heusler alloy. The degree of site (swap) disorder is systematically varied from 0% to 100% in steps of 12.5% using the supercell approach. DFT calculations reveal no considerable changes in the structural and magnetic properties of Co2MnAl by the presence of the disorder and are found to be the same as for the L21 structure. However, on the other hand, electronic properties such as, the spin polarization increased from 76% to 100% in the case of B2-25% and B2-75% disorder from the L21 structure resulting in half-metallic character. The study further suggests that static-magnetization and structural properties of Co2MnAl Heusler alloy are robust against site disorder.

Electron-magnon scattering in an anisotropic half-metallic ferromagnetic Weyl semimetal Co3Sn2S2

${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ is a magnetic Weyl semimetal, anisotropic ferromagnet, and half-metal in a single material. These qualities modify the spin dynamics and behavior of electron-magnon scattering. We have investigated this unconventional ferromagnet for modified electron-magnon scattering behavior using temperature and magnetic field dependent resistivity. ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ exhibits exponential suppression of spin-flip electron-magnon scattering below a characteristic crossover temperature which separates the regime of anomalous magnon scattering from one-magnon scattering. Interestingly, the Weyl fermion mediated spin dynamics with large magnetocrystalline anisotropy can also cause exponential suppression of electron-magnon scattering giving similar behavior in resistivity. The gap characterizing the suppression of electron-magnon scattering is 2.46(4) meV and increases linearly with magnetic field. The suppression of electron-magnon scattering could occur from half-metallic or anisotropic character but the presence of anomalous-magnon scattering at low temperatures evinces the half-metallic nature. A large anisotropy gap in magnon dispersion of half-metal can help prevent the deviation from 100% spin polarization at low temperatures.

Effect of 5d state-based full-Heusler alloys on the structural, electronic and magnetic properties of new half metallic ferromagnetism

First-principles calculations of structural, elastic, electronic and magnetic properties of full-Heusler Ir2HfB, Ir2HfAl and Ir2HfGa have been realized by full-potential linearized augmented plane wave (FP-LAPW) method implemented inWIEN2K code. The Perdew–Burke–Ernzerh of generalized gradient approximation (PBE-GGA) carried out the computation of different parameters to describe elastic and structural properties. The calculation of structural properties revealed that the three alloys are stable in cubic AlCu2Mn-type structure in ferromagnetic state. The elastic constants calculation shows the three alloys satisfy the stability criteria. Indeed, the calculated spin-polarized electronic band structure and density of states using generalized gradient approximation (GGA) show that Ir2HfZ (Z = B, Al, Ga) alloys have a metallic character. The influence of strong electronic correlation has been considered in GGA+Uand mBJ-GGA+U approximations that allows for improving the width of the band gap. The calculations carried out with GGA+U and mBJ-GGA+U show that Ir2HfAl and Ir2HfGa have a half-metallic behavior; however, Ir2HfB has a near half-metallic character. The calculated magnetic moments of Ir2HfB, Ir2HfAl and Ir2HfGa in a regular cubic structure with GGA+U and mBJ-GGA+U equal 1μB. With mBJ-GGA+U, the spin polarization values are 100% for Ir2HfAl, Ir2HfGa and 99.90% for Ir2HfBto be applicable for spintronics.

First-Principles Calculations of the Structural, Electronic, Optical, and Mechanical Properties of 21 Pyrophosphate Crystals

Pyrophosphate crystals have a wide array of applications in industrial and biomedical fields. However, fundamental understanding of their electronic structure, optical, and mechanical properties is still scattered and incomplete. In the present research, we report a comprehensive theoretical investigation of 21 pyrophosphates A2M (H2P2O7)2•2H2O with either triclinic or orthorhombic crystal structure. The molecule H2P2O7 is the dominant molecular unit, whereas A = (K, Rb, NH4, Tl), M = (Zn, Cu, Mg, Ni, Co, Mn), and H2O stand for the cation elements, transition metals, and the water molecules, respectively. The electronic structure, interatomic bonding, partial charge distribution, optical properties, and mechanical properties are investigated by first-principles calculations based on density functional theory (DFT). Most of these 21 crystals are theoretically investigated for the first time. The calculated results show a complex interplay between A, M, H2P2O7, and H2O, resulting in either metallic, half-metallic, or semi-conducting characteristics. The novel concept of total bond order density (TBOD) is used as a single quantum mechanical metric to characterize the internal cohesion of these crystals to correlate with the calculated properties, especially the mechanical properties. This work provides a large database for pyrophosphate crystals and a road map for potential applications of a wider variety of phosphates.