Half-metallic Band Gap Research Articles

High Curie temperature in Zn(Co,Ni)Se: DFT study

In this work, we aimed to examine the first-principles study of correlation between chemical environment and ferromagnetism, and Curie temperature of CoxZn1-xSe and NixZn1-xSe diluted magnetic semiconductors for different concentrations of impurity atoms. The calculations are implemented by the norm-concerving FHI pseudopotential method within the local spin density approximation (LSDA) and Hubbard U method. The analysis of the total density of states curves shows the half-metallic ferromagnetic character with half-metallic band gap. The first-principles calculated total magnetic moments of CoxZn1-xSe and NixZn1-xSe systems are found to be equal to 3 and 4 µB, respectively.

Deciphering the evolution of electronic and magnetic properties in alkali doped nickel oxide: An In-silico approach

In this study, we employed the DFT+U method to systematically explore the electronic, and magnetic properties of nickel oxide doped with alkali metal atoms (Li, Na, K). The Hubbard potential-U was judiciously applied to all doped compound resulting from alkali doping, and were found to exhibited half-metallic properties. A noteworthy observation was the half-metallic band gap in the spin-down channel, which exhibited a linear variation with the increasing value of the Hubbard potential. Furthermore, the total magnetic moment was discernible in the supercells, with all supercells demonstrating 100% spin polarization at the Fermi level. Consequently, the findings from this study hold significant potential for applications in spintronics, thereby paving the way for future research in this domain.

Structural stability, induced magnetism and half-metallic band gaps in Cr-substituted GaSb: novel prediction via semi-local potential

Structural stability, induced magnetism and half-metallic band gaps in Cr-substituted GaSb: novel prediction via semi-local potential

Investigating the multifaceted characteristics of Ba2FeWO6 double perovskite: Insights from density functional theory

This study undertook a comprehensive examination of the double perovskite complex Ba2FeWO6, investigating its structural, electrical, magnetic, thermal and elastic characteristics. The study used density functional theory (DFT), specifically the full potential linearized augmented plane wave (FP-LAPW) method. It also used different approximations, including the generalized gradient approximation (GGA) and the modified Trans-Blaha (TB-mBJ) approach, to improve the accuracy of the band gap estimation more accurate. Additionlly, the GGA + U approach, incorporating the Hubbard correction term (U), was utilized. Our findings indicate that Ba2FeWO6 exhibits indirect half-metallic band gaps in the (L-X) direction, with value of 0.91 eV and a net magnetic moment of 4 μB, predominatly influenced by the iron atom. The compound demonstrated exceptional characteristics suitable for thermoelectric applications, particularly at lower temperatures. Furthermore, the elasticity analysis revealed low brittleness, facilitates its manipulation in manufacturing procedures.

First-principles studies of the stability, structural, electronic, magnetic and optical properties of halogen atom doped marcasite FeS2

The effects of halogen atom (F, Cl, Br or I) doping on the stability, structural, electronic, magnetic and optical properties of marcasite FeS2 (m-FeS2) are investigated through the first-principles calculations. The formation energies are relatively small under Fe-rich condition, indicating that it is feasible to implant halogen atom into m-FeS2. The ground state of halogen atom doped m-FeS2 systems is magnetic due to the positive energy differences between non-spin-polarized and spin-polarized states. Phonon dispersion curves show that all doping systems are dynamically stable. The total magnetic moment of all doping systems is nearly 1μB, since replacing the S atom with a halogen atom introduces a non-bonding electron. Most of them come from Fe and S atoms, and only a small fraction come from the dopant. The simulation results show that F- and Br-doped m-FeS2 systems are still semiconductors although the band gaps are reduced considerably, Cl-doped m-FeS2 changes to a half-metal with half metallic band gap of 0.25 eV, while I-doped m-FeS2 becomes a metal, making them potentially useful in spintronics. In addition, the halogen atom doped m-FeS2 systems possess enhanced absorption coefficient and red-shifted absorption edge. So they are promising in optoelectronic device and solar energy harvesting.

The structure, magnetism and mechanical properties of L21-type full-Heusler alloy Cr2ZrSi: A first-principles study

Heusler alloy is a widely studied spintronic material in recent years, which has played a huge role in the field of spintronic devices due to its high spin polarization and high Curie temperature. Using first-principles calculation to predict the basic properties of Heusler alloy can not only save experimental costs and time but also provide a reliable theoretical basis for experimental research. This study used a first-principles calculation to study the magnetic and mechanical properties of full-Heusler alloy Cr2ZrSi with an L21-type structure. The research results indicate that the alloy is a half-metallic ferromagnetic material with a theoretical value of 100% spin polarization. The magnetism mainly comes from the asymmetric spin contribution of d-orbital electrons of transition metal atoms and their hybridization. At the same time, this complex hybridization coupling process is also a possible reason for the half-metallic band gaps. In terms of mechanical properties, the Cr2ZrSi alloy exhibits good ductility and anisotropy, with a Debye temperature of 303.848K. Our theoretical research results provide more choices and theoretical basis for subsequent experimental research.

The electronic structure and magnetic properties of stable Sr2BB′O5 (B = Fe, Co, Ni and B′ = Co, Ni, Mn) with the brownmillerite structure

First-principles calculations have been performed to investigate the structural, electronic, and magnetic properties of Sr2BB′O5 (B = Fe, Co, Ni; B′ = Co, Ni, Mn) brownmillerite materials. By considering the atomic arrangements and the tetrahedral rotated modes, including typical magnetic configurations, the ground states are found by comparing their total energy. The thermodynamic and dynamic stability studies revealed that two compounds, Sr2FeCoO5 and Sr2NiMnO5, could be stable in the brownmillerite structure. Further electronic structure calculations show that the ground state of Sr2FeCoO5 is a G-AFM insulator, while the ground state of Sr2NiMnO5 is an A-AFM half-metal with a half-metallic bandgap of about 1 eV, exhibiting excellent half-metallic properties. In addition, the magnetic interactions are analyzed, which suggest that Sr2FeCoO5 could suffer from the influence of the B-site atomic disorder to maintain the G-AFM state, while Sr2NiMnO5 is more sensitive to atomic disorder, so its A-AFM state would be easily destroyed by the B-site disorder. These results would be helpful for further research.

Thermoelectric, mechanical, and pressure sustained half-metallic properties of BaInO3 perovskite for spintronics applications: DFT computation

Oxide perovskites continue to promote research interest because of their concurrent use in spintronic and thermoelectric applications. The electronic, magnetic, and thermoelectric properties of new half-metallic BaInO3 perovskite are investigated using the density functional theory. The structural and thermodynamic stability of the proposed perovskite is provided by the tolerance factor, octahedral factor, formation energy, and phonon dispersion curves. The structural relaxation curves reveal that the ground state is ferromagnetic. The generalized gradient approximation and mBJ band structure plots show that the half-metallicity exclusively results from the strong exchange splitting of 2p-bands at the Fermi level. Compared with PBE, mBJ depicts highly localized magnetic moments around oxygen along with enhanced half-metallic gaps and band gaps in the spin-up channel. Under a compressive strain, the system undergoes a magnetic phase transition from half-metallic ferromagnet to non-magnetic metal at 30 GPa. The elastic stability at the studied pressure range has been verified from Blackman’s and Every’s diagrams. The material remains ductile and exhibits moderate elastic anisotropy in the studied pressure range. The quasi-harmonic Debye model is employed to study the temperature and pressure effects of thermodynamic parameters. The computed transport properties including the Seebeck coefficient and spin-Seebeck coefficient predict reasonable thermoelectric performance in generating thermally induced spin-polarized current and spin current, respectively. Such a detailed study of this material could open prospects in spintronic as well as waste energy recovery devices.

First principle studies on half-metallicity and pressure-induced half-metallic band gap in 3-d transition metal-based quaternary Heusler ScVCoZ (Z = Si, Ge, Sn, P, As, and Sb) alloys

In the present work, we predict a series of 3-d transition metals-based quaternary Heusler alloys (QHA) ScVCoZ (Z = Si, Ge, Sn, P, As, and Sb) (SVCZ), by employing density functional theory (DFT) calculations. We carried out extensive band structure (BS) and density of states (DOS) analysis to explain the half-metallic and magnetic behavior of the alloys. We found that SVCZ alloys stabilize in the F 4̅ 3m space group and exhibit a ferromagnetic (FM) ground state (GS). Among the QHAs, SVCZ (Z = Si, Ge, and Sb) exhibit intriguing half-metallic properties featuring 100% spin polarization at the Fermi level (EF). Additionally, the effect of pressure indicates a band gap opening in one of the spin channels for SCVZ (Z = P, and As), and the half-metallic characteristics are retained up to a compressive pressure, respectively of 65, and 79 GPa for SCVP and SCVAs. Elastic properties calculations suggest SVCZ alloys satisfy Born stability criteria and are mechanically stable. Among the predicted QHAs, SVCZ (Z = Si, Ge, and Sn) shows brittle nature, whereas SVCZ (Z = P, As, and Sb) are ductile.

First-principles simulations of magnetic properties of Co- and Ni-doped ZnSe

We purposed to analyze the theoretical ab initio study of ferromagnetism and to estimate Curie temperature of Co2+ and Ni2+ 3d transition metal (TM) ions doped Zn1-x TM x Se compounds for 12.5 % and 6.25 % concentrations of impurity TM(Co, Ni) atoms. The calculations are carried out using the norm-conserving Fritz-Haber-Institute ionic pseudopotentials based on density functional theory within the local spin density approximation and Hubbard U (U(Znd)=4.5 eV; U(Sep)=3.8 eV) corrections. The analysis of the total and partial electron density of states shows the half-metallic ferromagnetic behavior with a half-metallic bandgap. The theoretically obtained total magnetic moments of TM(Co, Ni) doped Zn1-x TM x Se systems are equal to 3 μB and 4 μB, correspondingly.

Influence of main-group elements on structural, electronic, magnetic and half-metallic properties of DO3-type Mn3Z (Z = Al, Ga, In, Si, Ge, Sn, P, As and Sb) alloys - A DFT study

We investigate the influence of main-group elements belonging to group III (Al, Ga and In), IV (Si, Ge and Sn) and V (P, As and Sb) on structural, electronic, magnetic and half-metallic (HM) properties of DO3-type Mn3Z alloys using density functional theory (DFT). In particular, we emphasize on the correlation between structural parameters (lattice constant) and the changes in electronic and magnetic properties of Mn3Z alloys. From full geometry optimization results, we find that the entire Mn3Z alloys stabilized to ferrimagnetic ordering. Further, the spin-polarized density of states (DOS) calculation reveals that Mn3Z (Z = Al, Si, Ge, Sn, As and Sb), Mn3Ga and Mn3In alloys exhibit, respectively, half-metallic (HM), nearly half-metallic (NHM) and metallic nature. While, the Mn3P alloy displays spin-gapless semiconducting (SGS) feature, in which spin-up and spin-down channels show metallic and spin-gapless feature, respectively. The Mn3Al, Mn3Z (Z = Si, Ge and Sn) and Mn3Z (Z = P, As and Sb) alloys follow Slater-Pauling rule well, and gives 100 % spin-polarization at the Fermi energy (EF) with total integer magnetic moment of 0, 1 and 2 μB/f.u, respectively. The contribution to total magnetic moment in all the Mn3Z alloys comes predominantly from Mn(Y) atoms. The molecular orbital (MO) hybridization mechanism is proposed to rationalize the HM band gap.

Theoretical Investigation of Half-metallicity and Pressure-induced Half-metallic Band Gap in Half Heusler RuMnZ (Z = Si, Ge, Sn, P, As, Sb, Se, and Te) Alloys

Theoretical Investigation of Half-metallicity and Pressure-induced Half-metallic Band Gap in Half Heusler RuMnZ (Z = Si, Ge, Sn, P, As, Sb, Se, and Te) Alloys

Systematic investigation of magneto-electronic, structural, thermoelectric and optical properties of Nd2MgX4 (X = S, Se) compounds

The structural, magnetic, optoelectronic, and thermoelectric (TE) characteristics of Nd2MgX4 (X = S, Se) are determined by utilizing the density functional theory (DFT) based full potential linearized augmented plane wave (FP-LAPW) method as employed in WEIN2k code. The exchange and correlation energies along with Coulomb interactions are brought into consideration by employing local density of approximation with Hubbard model (LDA+U). Tolerance (τ) factor and formation enthalpy were utilized to confirm the stability of both spinels. τ values are 0.70 and 0.68, and formation enthalpy values are (ΔHf) are -3.34 eV and -2.19 eV for Nd2MgX4 (X = S, Se), respectively. For Nd2MgX4 (X = S, Se) metallic behavior is found in spin up case while considerable bandgaps are found in spin down with half metallic bandgap (Eg) values of 1.82 and 1.26 eV (in spin down), correspondingly. The calculated magnetic moment for Nd2MgX4 (X = S, Se) are 12.0008 μB and 12.0003 μB, respectively. Furthermore, optical features including refractive index n(ω), dielectric constant 𝜀𝜀(𝜔𝜔), reflectivity R(ω), optical conductivity σ(ω), absorption coefficient α(ω) and extinction coefficient k(ω) are computed. The maximum calculated real part of dielectric constant 𝜀𝜀1(𝜔𝜔) values for Nd2MgX4 (X = S, Se) are 9.2 and 10.8, respectively. For Nd2MgX4 (X = S, Se), σ(ω) has maximum value of 7642.9 at 6.6 and 7592.5 (Ω cm)-1 at 5.99 eV, respectively. The various temperature dependent thermoelectric (TE) parameters along with figure of merit (ZT) are determined to get full insight into the TE behavior for both compounds by using BoltzTraP code. The computed ZT value for Nd2MgSe4 is 0.81 at 800 K while Nd2MgS4 has ZT value of 0.80 at 800 K. Results showed that both spinels have potential in spintronics and in cooling industries.

Tunable magnetic anisotropy, half-metallicity and tunneling magnetoresistance effect of 2D CrI3 in CrI3/MnGeX3 (X = Se, Te) heterostructures under normal compressive strain

The induction of half-metallicity and tunable magnetic anisotropy of CrI3 monolayers remains challenging and unstable. In this study, we demonstrate that half-metallic CrI3 can be induced in a CrI3/MnGeX3(X = Se, Te) heterostructure. Normal compressive (NC) strain can effectively control the half-metallic band gap and spin-polarized electronic transport of CrI3 in CrI3/MnGeSe3. At 6% strain, the half-metallic band gap and equilibrium tunneling magneto-resistance (TMR) increases by 25% and 220%. The results of band structure, force theorem, charge density and work function calculations show that CrI3 in CrI3/MnGeSe3 loses electrons to form a hole-conducting half-metal with in-plane easy magnetization axis, while CrI3 gains electrons in CrI3/MnGeTe3 to form an electron-conducting half-metal with out-of-plane easy magnetization axis. Heterointerfacial half-metallicity in CrI3 is intrinsic without any external physical modification, and the NC strain of a two-dimensional structure can easily be realized experimentally, paving the way for further research of spintronic devices.

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.

Half-Metallic Bandgap Measurement Using Circularly Polarized Infrared Light

One avenue toward next-generation spintronic devices is to develop half-metallic ferromagnets with 100% spin polarization and Curie temperature above room temperature. Half-metallic ferromagnets have unique density of states, where the majority spins are metallic but the minority spins are semiconducting with the Fermi level lying within an energy gap. To date, the half-metallic bandgap has been predominantly estimated using Jullière’s formula in a magnetic tunnel junction or measured by the Andreev reflection at low temperature, both of which are very sensitive to the surface/interface spin polarization. Alternative optical methods such as photoemission have also been employed but with a complicated and expensive setup. In this study, we developed and optimized a new technique to directly measure the half-metallic bandgap by introducing circularly polarized infrared light to excite minority spins. The absorption of the light represents the bandgap under a magnetic field to saturate the magnetization of a sample. This technique can be used to provide simple evaluation of a half-metallic film.

Influence of 3d-Fe substitution on structural, mechanical, electronic, and magnetic properties in rock-salt SrS: Insights from the first-principles study

In the present work, first-principles calculations are carried out to investigate the impact of strontium (Sr) replacement by iron (Fe) atoms on the structural, mechanical, electronic, and magnetic properties of rock-salt Sr1-xFexS (0.125≤x≤0.75) compounds. Our calculation results show that the non-magnetic semiconductor-to-ferromagnetic half-metal-to magnetic metal transition and the indirect-to-direct-to-indirect bandgap transition can be realized by altering the Fe concentration. Further analysis indicates that this alteration affects the half-metallic bandgaps, magnetic moments, and exchange constants. The induced ferromagnetism and half-metallicity are attributed to the p-d hybridization between 3d-Fe and 3p-S states. A mechanical study is performed, and it is found that all the titled compounds are mechanically stable. Meanwhile, the high ratio of bulk modulus to shear modulus (B/G) suggests that they are ductile. Finally, an evaluation of the Debye temperature and melting point reveals the potential for the examined compounds to be used in thermal applications.

Intrinsic half-metallicity in two-dimensional Cr2TeX2 (X = I, Br, Cl) monolayers.

Two-dimensional (2D) materials with intrinsic half-metallicity at or above room temperature are important in spin nanodevices. Nevertheless, such 2D materials in experiment are still rarely realized. In this work, a new family of 2D Cr2TeX2 (X = I, Br, Cl) monolayers has been predicted using first-principles calculations. The monolayer is made of five atomic sublayers with ABCAB-type stacking along the perpendicular direction. It is found that the energies for all the ferromagnetic (FM) half-metallic states are the lowest. The phonon spectrum calculations and molecular dynamics simulations both demonstrate that the FM states are stable, indicating the possibility of experimentally obtaining the 2D Cr2TeX2 monolayers with half-metallicity. The Curie temperatures from Monte Carlo simulations are 486, 445, and 451 K for Cr2TeI2, Cr2TeBr2, and Cr2TeCl2 monolayers, respectively, and their half-metallic bandgaps are 1.72, 1.86 and 1.90 eV. The corresponding magnetocrystalline anisotropy energies (MAEs) are about 1185, 502, 899 μeV per Cr atom for Cr2TeX2 monolayers, in which the easy axes are along the plane for the Cr2TeBr2 and Cr2TeCl2 monolayers, but being out of the plane in the Cr2TeI2. Our study implies the potential application of the 2D Cr2TeX2 (X = I, Br, Cl) monolayers in spin nanodevices.

Comparison of Electronic and Magnetic Properties of 4d Transition Metals Based NbAl2F4 and TcAl2F4 Spinels

Half-metallic properties of NbAl2F4 spinel and semiconductor characteristics of TcAl2F4 spinel were investigated with the help of the WIEN2k program. NbAl2F4 spinel shows a metallic character in the up-electron states, while it has a semiconductor nature in the down-electron states. In NbAl2F4 spinel, the Eg bandgaps were calculated in GGA and GGA+mBJ 1.551 eV and 1.622 eV, respectively. The EHM half-metallic bandgaps were obtained 0.410 eV and 0.422 eV, respectively. In the up-spin states of TcAl2F4 spinel, Eg values were obtained 1.199 eV and 1.447 eV for the GGA and GGA+mBJ methods, respectively, while they were obtained 1.281 eV and 1.519 eV in the down-spin states, respectively. When GGA+mBJ is used, it is easily observed that the semiconductor characters increase. Total magnetic moments of NbAl2F4 and TcAl2F4 spinels were calculated 6.00 µB/cell and 10.0 µB/cell, respectively. When both electronic and magnetic moment values are carefully examined, NbAl2F4 and TcAl2F4 spinels can be used as alternative compounds in spintronic applications.

Predicting and understanding the structural stability, origin of half-metallic magnetic nature, and study of opto-electronic properties of Cs2KXCl6: X = Ti and V double perovskites

A succinct summary of various physical characteristics of halide double perovskites Cs2KXCl6: (X = Ti and V) has been summarized using Density Functional Theory (DFT), as applied in WIEN2k simulation code. These material’s stability in Fm-3 m cubic symmetry is confirmed by structural optimization, tolerance factor and elastic parameters. The electronic band structures and density of states calculated using GGA and GGA+mBJ show that these materials are semiconducting in spin down channels. The crystal field splitting of d-orbitals is used to explain the semiconducting ferromagnetic nature of these Ti- and V- based halide double perovskites. The ferromagnetic character of these double perovskites is suggested by the optimization and asymmetric DOS across Fermi level. We have also discussed about the origins of half-metallic bandgap and magnetism. The total magnetic moments of the Ti and V-based double perovskites are 1μB and 2μB, respectively, with the transition metal atoms (Ti/V) accounting for the major contributions. At the Fermi level, these double perovskites have 100% spin polarization, indicating that they could be used in spintronics.