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Abstract In this study, the structural and electronic properties of CoX 0.25 S 1.75 (X = F, Cl, or Br) were investigated based on spin-polarized first-principles calculations. S-F, S-Cl, and S-Br covalent bonds are not present in CoX 0.25 S 1.75 (X = F, Cl, or Br). The generalized gradient approximation (GGA) + U and Heyd-Scuseria-Ernzerhof hybrid functional method may overestimate the spin-down band gap for CoS 2. The results obtained for CoX 0.25 S 1.75 (X = F, Cl, or Br) using the GGA method are expected to be more reasonable. Only the half-metal CoF 0.25 S 1.75 can be used for spintronic applications and the metal CoX 0.25 S 1.75 (X = Cl or Br) is more suitable for use in supercapacitors. The p - d hybridization between S and Co atoms in CoF 0.25 S 1.75 is stronger compared with that in CoS 2. The p - d hybridization between S(S-X) and Co atoms is stronger whereas that between S(S-S) and Co atoms is weaker in CoX 0.25 S 1.75 (X = Cl or Br). Doping with F and Cl (Br) atoms in CoS 2 induces new bands with less and more dispersion, respectively. In CoX 0.25 S 1.75 (X = F or Cl), X atoms gain more electrons than S atoms and the charge density difference indicates that S atoms donate electrons to F and Cl atoms. However, in CoBr 0.25 S 1.75 , Br atoms gain fewer electrons than S atoms and there is almost no charge transfer between S and Br atoms. Graphical abstract Image 1 Highlights • Results obtained for CoX 0.25 S 1.75 by GGA method are expected to be more reasonable. • CoF 0.25 S 1.75 is half–metallic and can be used for spintronic applications. • CoCl 0.25 S 1.75 and CoBr 0.25 S 1.75 are more suitable for use in supercapacitors. • Doping CoS 2 with F/Cl (Br) atoms induced new bands with less/more dispersion. [ABSTRACT FROM AUTHOR]

According to electronic structure calculations based on density functional theory, we predicted and studied the structural, mechanical, electronic, magnetic, and transport properties of a new full Heusler chalcogenide called Fe 2 CrTe in both its bulk and heterostructure forms. This system exhibits ferromagnetic and half-metallic (HM)-like behavior, with very high (about 95%) spin polarization at the Fermi level in its cubic phase. Interestingly, under tetragonal distortion, a clear minimum (with almost the same energy as the cubic phase) was found at a c/a value of ∼ 1.26, but it exhibits ferrimagnetic and fully metallic characteristics. The compound was found to be dynamically stable against lattice vibration in both phases. The elastic properties indicate that the compound is mechanically stable in both phases according to the stability criteria for the cubic and tetragonal phases. The elastic parameters demonstrate the mechanically anisotropic and ductile nature of the alloy system. Due to the HM-like behavior of the cubic phase and considering practical aspects, we probed the effect of strain and the substrate on various physical properties of the alloy. The transmission profile was calculated for the Fe 2 CrTe/MgO/Fe 2 CrTe heterojunction to investigate its possible use as a magnetic tunneling junction material in both the cubic and tetragonal phases. A large tunneling magnetoresistance ratio of ≈ 1 0 3 % was determined for the tetragonal phase and it was one order of magnitude larger than that for the cubic phase. • We predict a novel full Heusler chalcogenide - Fe 2 CrTe. • It shows a ferromagnetic and half-metal(HM)-like behavior in the cubic phase. • Volume conserved tetragonal phase exhibits ferrimagnetic and metallic nature. • Dynamical and mechanical stability are predicted in both the phases. • Under negative uniform strain, cubic phase shows fully HM-like behavior. • Promising spin-transport properties for Fe 2 CrTe/MgO/Fe 2 CrTe is observed. [ABSTRACT FROM AUTHOR]

Effect of Cr doping on the magnetic structure and electronic properties of Fe 2 VSi has been investigated by experimental measurement and first-principles calculations. In Fe 2 V 1-x Cr x Si, ferromagnetism can be stabilized with 10% Cr substitution. The Curie temperature T C increases rapidly with increasing Cr content and reaches 365K when x = 0.4. The saturation magnetization M s also increases with increasing Cr content. A small amount of A15 secondary phase is observed with increasing Cr content at x = 0.4, indicating that the solid solubility of Cr in Fe 2 VSi has been reached. In Fe 2 V 1-x Cr x Si, high spin polarization ratio is predicted when x ≥ 0.25, and half-metallic character is observed when x = 0.5, 0.75 and 1.0. The calculated total spin moment M t also increases with increasing x. When x is larger than 0.2/0.25, the experimental/theoretical total moment gets close to the Slater-Pauling curve of M = Z - 24 for half-metallic Heusler alloys. All this makes Fe 2 V 1-x Cr x Si promising candidates for spintronic applications. [ABSTRACT FROM AUTHOR]

The electronic, magnetic and optical properties of C- and N-doped CeO 2 bulk and (111) surface have been systematically investigated by first-principles calculations. The results show that the spin splitting occurs when doping atoms replace the anion sites in the CeO 2 matrix, causing a local magnetic moment of 2.00, and 1.00 μ B for C- and N-doping, respectively. The strong hybridization between dopants 2 p and O 2 p triplet-states around the Fermi level gives rise to the half-metallic character for doped bulk systems, while substitution onto the surface eliminates the degeneration of dopants 2 p orbitals, which results in anisotropic spin atmosphere. Especially, owing to the low formation energy and available RTFM, N-doped CeO 2 would be easily realized in the experiment and should also be wonderful candidate materials for oxide spintronics. In addition, compared with N-doped CeO 2 , the calculated optical properties reveal that C-doped CeO 2 (111) surface is able to enhance the absorption of the visible light. [ABSTRACT FROM AUTHOR]

The effects of 3 d transition metals doping on the structural, electronic, and magnetic properties of aluminum hydride were investigated based on spin-polarized first-principles calculations. The studies indicated that V, Cr, Mn, and Fe doping could produce polarization of high-spin state, while Co and Ni doping would induce polarization of low-spin state. It was found that the magnetic ground state depended on the distance between two substitutions and the long-range ferromagnetic coupling was achieved upon doping V, Mn, and Fe. The present work indicated that the introduced 3 d -block dopants could tailor aluminum hydride into either a potential half-metallic or n -type magnetic semiconductor by tuning the valence electrons of the impurities. The main findings of this work pointed out the possibilities of the applications of hydrides in future hydride electronics and spintronics. [ABSTRACT FROM AUTHOR]

Investigation of band structure and thermo-physical response of new quaternary CoVTiAl Heusler alloy within the frame work of density functional theory has been analyzed. 100% spin polarization with ferromagnetic stable ground state at the optimized lattice parameter of 6.01 Å is predicted for the compound. Slater-Pauling rule for the total magnetic moment of 3 µ B and an indirect semiconducting behavior is also seen for the compound. In order to perfectly analyze the thermo-physical response, the lattice thermal conductivity and thermodynamic properties have been calculated. Thermal effects on some macroscopic properties of CoVTiAl are predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variations of the lattice constant, volume expansion coefficient, heat capacities, and Debye temperature with pressure and temperature in the ranges of 0 GPa to 15 GPa and 0 K to 800 K have been obtained. [ABSTRACT FROM AUTHOR]

In this study, density functional theory (DFT) showed that the electronic band profiles of CaCu 3 B 2 Re 2 O 12 (B = Mn, Fe, Co, and Ni) indicate their half-metallic character. The optimized magnetic energy curves in different magnetic phases demonstrated the type-I ferrimagnetic order of all the compounds investigated in this study. The magnetic exchange coupling constants were calculated between the Cu–B, B–Re, and Cu–Re site spins using the Heisenberg model. These interactions generate strong long range Cu(↑)B(↑)Re(↓) order through a super-exchange mechanism. In these perovskites, the anti-parallel moments of Re with B and Cu reduce the net magnetic moments and they are responsible for the ferrimagnetism. The Cu and B 3d-electrons are localized and responsible for the magnetism, and the Re 5d-electrons are delocalized and responsible for the metallic nature. Magnetic susceptibility analysis verified the results estimated using DFT and the Heisenberg model. Due to the 100% spin polarization around the Fermi level, high Curie temperature TC and ferrimagnetism are expected, thereby making these materials suitable for spintronic applications. • The half-metallic character of the CaCu 3 B 2 Re 2 O 12 (B = Mn, Fe, Co and Ni) was revealed by DFT. • Heisenberg model was used for the calculating of the magnetic exchange coupling constants. • It has been shown the perspectives of the CaCu 3 B 2 Re 2 O 12 (B = Mn, Fe, Co and Ni) in spintronic applications. [ABSTRACT FROM AUTHOR]

A systematic and comparative theoretical study on the stabilization mechanism of titanium cluster has been performed by selecting the clusters Ti n ( n =3, 4, 5, 7, 13, 15 and 19) as representatives in the framework of density-functional theory. For small clusters Ti n ( n =3, 4 and 5), the binding energy gain due to spin polarization is substantially larger than that due to structural distortion. For medium clusters Ti 13 and Ti 15 , both have about the same contribution. For Ti n ( n =4, 5, 13 and 15), when the undistorted high symmetric structure with spin-polarization is changed into the lowest energy structure, the energy level spelling due to distortion fails to reverse the level order of occupied and unoccupied molecular orbital (MO) of two type spin states, the spin configuration remains unchanged. In spin restricted and undistorted high symmetric structure, d orbitals participate in the hybridization in MOs, usually by way of a less distorted manner, and weak bonds are formed. In contrast, d orbitals take part in the formation of MOs in the ground state structure, usually in a distorted manner, and strong covalent metallic bonds are formed. [ABSTRACT FROM AUTHOR]

The electronic structure and magnetic properties of the SnO 2 (001) surface doped with a nonmetal (C or N) and a transition metal (Co or Ni) were studied by first-principles calculations based on density functional theory. The pristine SnO 2 (001) surface is a nonmagnetic insulator. Although the two-coordinated oxygen vacancy (V O2c) has the lowest formation energy, it cannot produce spin polarization on the SnO 2 (001) surface, while both C and N can introduce spin-splitting defect states in the band gap. It is shown that a single C (or N) atom can produce a magnetic moment of 1.99 μ B (or 0.99 μ B) on the surface. In addition to the local magnetic moment on the dopant atom, many spins are distributed in the crystal gap. Calculations with the generalized gradient approximation with Coulomb repulsion U show that Co (or Ni) can produce a magnetic moment of 1.0 μ B (or 2.0 μ B) in the system, but the spin polarization occurs mainly in the valence band. Studies on magnetic coupling between dopant atoms at different distances show that only Co–Co exhibits mainly ferromagnetic coupling, while C–C, N–N, and Ni–Ni are dominated by antiferromagnetic coupling. Therefore, doping with Co can produce a relatively stable macroscopic magnetism. [Display omitted] • Oxygen vacancy cannot produce d 0 ferromagnetism on the SnO 2 (001) surface. • Both C and N can produce spin splits in the band gap on the surface. • The spin polarization caused by the Co (or Ni) atom occurs in the valence band. • Only Co–Co at different distances exhibits mainly ferromagnetic coupling. [ABSTRACT FROM AUTHOR]

A first-principles theoretical study of the enhanced electronic and magnetic properties of a single-layer CdS (denoted as SL-CdS) was conducted via Li substitutional doping at possible sites. Previous work shows that SL-CdS is a non-magnetic and direct bandgap semiconductor. Our work demonstrated that electronic bandgap tuned to smaller and larger values, e.g., the calculated bandgap (pseudo bandgap) for Li Cd (Li h) are 1.80 eV and 1.62 eV, respectively. Local magnetic moment induced via Li atomic doping at possible dopants sites except for Li h. The Li Cd gives a maximum magnetic moment of 0.98 μ B and shows the half-metallic character with a small dispersion for the spin-down channel at the Γ point. Among all the possible sites, the Li Cd in SL-CdS is magnetic and being most favorable thermodynamically under both S-rich and Cd-rich conditions. The Li Cd in SL-CdS indicates spin polarization with increased bandgap for spin-up and spin-down channels. In contrast, the Li S induces a magnetic moment of 0.86 μ B with a reduced bandgap of 0.60 eV for both the spin-up and spin-down channels. The partial magnetic moment is due to the fact small concentration of the dopant. Interestingly, Li h in SL-CdS shows non-magnetic semiconducting nature with decreased bandgap. For further investigation, we considered the most favorable Cd-Site. For room-temperature ferromagnetism, we did ferromagnetic and anti-ferromagnetic calculations. We considered interactions between two Li atoms substituted at far positions (1, 2) and near positions (1, 3) in SL-CdS. It was found that 2Li Cd in SL-CdS at near positions (1, 3) has FM order with Curie temperature (T c) of 339.95 K at − 5 % compressive biaxial strain. The effect of Li doping on electronic and magnetic properties of SL-CdS can help to utilize SL-CdS materials in electronics and spintronics devices applications. • We select nitrogen (Li) as a first-row element that could host spin-polarized electrons in its s-orbitals as possible sources of magnetic moment, and study various possible dopant positions. • The main aims of our study are (i) tuning of the electronic bandgap (ii) inducing magnetic moments in diamagnetic single-layer CdS. • Studying ferromagnetic (FM) and antiferromagnetic (AFM) coupling to predict the more favorable state. • Our material shows three simultaneous properties of ferromagnetism, diamagnetism and semiconducting one. • To the best of our knowledge, no 2D material is predicted to have such high temperature stability of these properties to-date. [ABSTRACT FROM AUTHOR]

The electronic structure and magnetism properties of V-doped monolayer MoS 2 under biaxial strains were researched through the first-principle calculations. The V-doped MoS 2 is a p-type semimetal with ferromagnetism (FM) state at zero strain, of which V–MoS 2 and V atom exhibit the magnetic moment of 0.81 and 0.30 μ Β , respectively. However, as the biaxial tensile strain is applied and increased gradually, the ground state changes from ferromagnetism (FM) to anti-ferromagnetism (AFM) and the magnetic moment simultaneously reduces. When the biaxial tensile strain is 3%, the ground state of the system turns into the AFM state. Moreover, under biaxial compressive strain, the system also changes from ferromagnetism (FM) to anti-ferromagnetism (AFM). The magnetism and stability of the FM state are weakened gradually due to the strengthened ionic characteristics of Mo–S bonds and the non-localization d orbitals of Mo and V atoms. The results provide a path to adjust the electronic states and magnetism characteristics of 2D transition metal dichalcogenides (TMDs), paving the way for application in spintronic devices. Slight doping with V leads to spin polarization which weakens and even disappears at large tensile strain depending on the increased ionic character of Mo and S bonds and resultant delocalization of Mo d orbitals. Image 1 • FM features of V-doped monolayer MoS 2 are weakened under tensile strain. • V-doped monolayer MoS 2 is changed into AFM state at the biaxial tensile strain of 3%. • The FM stability is lowered and even disappears because of the increased ionic character of Mo and S bonds and resultant delocalization of Mo d orbitals. [ABSTRACT FROM AUTHOR]