Stability Of Ferromagnetic State Research Articles

Tunability of half metallicity and thermoelectric indicators in Na2TaX6 (X = Cl, Br) vacancy ordered double perovskites

With the growing development in spintronics and thermoelectrics, researchers across the globe are extensively trying to fabricate and characterize novel materials. In this regard, the current work analyses the magnetic and thermoelectric characteristics of vacancy-ordered double perovskites Na2TaX6 (X = Cl, Br) computed using density functional theory. The geometry optimization reveals a cubic crystal structure with a relatively more stable ferromagnetic state. The mechanical and thermodynamic stability analyses also indicate the stability of both compounds. The computed electronic band structures demonstrate a half-metallic (HM) nature with metallic behavior in the up-spin channel. A semiconducting nature in down-spin configuration shows a direct bandgap of 3.6 eV and 4 eV for Na2TaCl6 and Na2TaBr6, respectively. The computation of transport parameters is found suitable for thermoelectric device applications. The present study demonstrates the high potential of the examined materials for applications in energy conversion and spintronics devices.

Half-Metal Ferromagnetism V-Doped GaN Nanosheet Application in Spintronic Device

The density functional theory calculations using general gradient approximation (GGA) have been systematically performed to study the electronic structures, the density of states (DOS), and magnetic properties of V-doped GaN nanosheet for different dopant concentrations (2.08% and 4.16%). We conducted the entire study using the Atomistixtool kit code. The electronic properties were improved with the Hubbard values U = 4 eV. V-doped CaN nanosheet exhibits stable ferromagnetic (FM) states relative to corresponding antiferromagnetic (AFM) states. The calculated TC with the V-doping is found to be above the room temperature (RT) one. Calculation results reveal that V-doped nanosheets may be a good candidates for spintronics due to its good half-metal ferromagnetism.

The mysterious magnetic ground state of Ba14MnBi11 is likely self-doped and altermagnetic

Magnetism in the Zintl compound Ba14MnBi11 is rather poorly understood. Experimental claims are largely inconsistent with ab initio calculations, much beyond typical errors of the latter. We revisit this old problem, assuming that the root of the problem may be in nonstoichiometry of existing samples. Our key finding is that the magnetic ground state is indeed very susceptible to charge doping (band filling). Calculations for stoichiometric Ba14MnBi11 give a rather stable ferromagnetic metallic state, in agreement with previous publications. However, by adding exactly one electron per Mn, the system becomes semiconducting as expected, and becomes weakly antiferromagnetic (AF). On the other hand, upon small amount of hole doping, the system transitions to a special type of AF state known as altermagnetism. Furthermore, hole and electron doping-induced phase transitions result from different underlying mechanisms, influencing different exchange pathways. We propose that the inconsistency between experiment and theory is not a failure of the latter, but results from a nontrivial ramification of nonstoichiometry. The possibility of doping-stabilized altermagnetism is exciting.

Study of half-metallic ferromagnetism and transport properties of Cs2XI6 (X = transition metals) for spintronic and energy harvesting applications

The double perovskites (DPs) are an emerging applicant for spintronic devices. In the present paper, the ferromagnetism, Curie temperature, and transport characteristics of Cs2XI6 (X = Ta, W, Re, Os) are controlled by the 5d-electrons of transition metal ions. The optimization curves indicate the stability of ferromagnetic states because the energy released in ferromagnetic states is greater than in antiferromagnetic states. The formation energy and phonons dispersion calculations confirmed thermodynamic and dynamic stabilities, while the Goldsmith tolerance factor ensured structural stability. The Heisenberg model and polarization density findings ensure ferromagnetism at high temperatures and 100 % spin polarization. Furthermore, the analysis of the band structures and density of states shows that half-metallic ferromagnetism has a major contribution from 5d-X and 5p-I states. The hybridization, double exchange model, exchange constants, and crystal field energies are also reported for the comprehensive study of the origin of ferromagnetism. Finally, the Seebeck coefficients, electrical and thermal conductivities, and thermoelectric power are illustrated comprehensively. The significant values of the figure of merit make these materials potential candidates for energy harvesting applications.

Exploring the Mn doped BaTe alloy for spintronics and energy harvesting applications

In the present study, the ferromagnetic semiconductor behavior of Mn doped BaTe is reported along with their physical properties. The calculations are done by full potential linearized augmented plane wave (FP-LAPW) approach within spin-polarized density functional theory (SP-DFT). Formation energies were computed to satisfy the stability of reported alloys. The spin-polarization is included in the calculations to study the electronic (band structure (BS), density of states (DOS)) and magnetic characteristics. Ba1−xMnxTe elucidates the magnetic semiconductor nature with direct band gap (Eg) in both spin channels while indirect Eg (1.66 eV) is observed for pure BaTe compound. Stable ferromagnetic (FM) states are vindicated owing to the p-d hybridization which are contributors in inducing magnetic moments (μ B) at interstitial and non-magnetic sites. The optical parameters (reflectivity, absorption coefficient, refraction, optical conductivity and dielectric function) were computed within an energy range of 0–10 eV. Thermoelectric (TE) features are also figured using Boltaz-Trap code in terms of thermal and electrical conductivity, figure of merit, Seebeck coefficient and power factor. The analysis of optical parameters suggests that the considered alloys is active within visible to UV-range, having potential applications in optoelectronic, photovoltaic and thermoelectric applications.

Controlling the 2D Magnetism of CrBr3 by van der Waals Stacking Engineering.

The manipulation of two-dimensional (2D) magnetic order is of significant importance to facilitate future 2D magnets for low-power and high-speed spintronic devices. van der Waals stacking engineering makes promises for controllable magnetism via interlayer magnetic coupling. However, directly examining the stacking order changes accompanying magnetic order transitions at the atomic scale and preparing device-ready 2D magnets with controllable magnetic orders remain elusive. Here, we demonstrate the effective control of interlayer stacking in exfoliated CrBr3 via thermally assisted strain engineering. The stable interlayer ferromagnetic (FM), antiferromagnetic (AFM), and FM-AFM coexistent ground states confirmed by the magnetic circular dichroism measurements are realized. Combined with the first-principles calculations, the atomically resolved imaging technique reveals the correlation between magnetic order and interlayer stacking order in CrBr3 flakes unambiguously. A tunable exchange bias effect is obtained in the mixed phase of FM and AFM states. This work will introduce new magnetic properties by controlling the stacking order and sequence of 2D magnets, providing ample opportunities for their application in spintronic devices.

Unveiling the Robust Struct-Electromagnetic Characteristics of CdAB2 Chalcopyrite (A = Cr, Mn, Fe; B = P, As): A Comprehensive Ab-Initio Study

We present a comprehensive investigation of the electromagnetic properties of CdAB2 compounds, where A represents Cr, Mn, or Fe, and B denotes P or As. To investigate the spin-polarized behavior of these compounds the A atoms were substituted at the Group IV (Ge) position in CdGeB2 in the chalcopyrite crystal structure. Our results reveal that all the CdAB2 compounds exhibit compelling spin-splitting of energy states near the Fermi level (EF). Notably, CdAB2 materials with A = Cr and Mn exhibit intriguing half-metallic ferromagnetic (HMF) characteristics, with the calculated total magnetic moments of 2.00 and 3.00 µB/f.u., respectively. The HMF properties originated in CdAB2 (A = Cr and Mn; B = P, As) these compounds owing to the hybridization of partially filled -3d(t2g) states of A atoms with the p-states of B (P, As) atoms, with minor contributions from Cd’s-like states. In contrast, CdFeB2 displays distinct behavior, demonstrating spin-splitting of energy levels around the EF indicative of a stable ferromagnetic (FM) state and the absence of HMF at their equilibrium volume. The calculated total magnetic moments for CdFeP2 and CdFeAs2 are about 1.83 (1.64 µB/f.u.) and 1.94 µB/f.u. (1.84 µB/f.u.) under generalized gradient approximation (GGA) (local spin density approximation (LSDA)) approximations, respectively. Perhaps these CdAB2 compounds (A = Cr and Mn; B = P, As) with HMF characteristic within both LSDA and GGA formalisms makes them highly promising candidates for spin injectors in the spintronic device applications. Furthermore, their semiconducting nature renders CdCrB2 and CdMnB2 materials compatible with silicon and other semiconducting lattices, enhancing their potential practical applications in the spintronic technologies. In conclusion, this study presents a thorough exploration of the robust electronic and magnetic properties of CdAB2 chalcopyrites, offering exciting prospects for their utilization in the future spintronic applications.

Electron doping induced stable ferromagnetism in two-dimensional GdI3 monolayer

As a two-dimensional material with a hollow hexatomic ring structure, Néel-type anti-ferromagnetic (AFM) GdI3 can be used as a theoretical model to study the effect of electron doping. Based on first-principles calculations, we find that the Fermi surface nesting occurs when more than 1/3 electron per Gd is doped, resulting in the failure to obtain a stable ferromagnetic (FM) state. More interestingly, GdI3 with appropriate Mg/Ca doping (1/6 Mg/Ca per Gd) turns to be half-metallic FM state. This AFM–FM transition results from the transfer of doped electrons to the spatially expanded Gd-5d orbital, which leads to the FM coupling of local half-full Gd-4f electrons through 5d–4f hybridization. Moreover, the shortened Gd–Gd length is the key to the formation of the stable ferromagnetic coupling. Our method provides new insights into obtaining stable FM materials from AFM materials.

Theoretical study of rare earth in the spinels chalcogenide MgCe2Z4 (Z = S, Se) for spintronic and thermo-electric applications

For leading spintronic technology, the significance of rare earth in the spinels chalcogenide MgCe2Z4 (Z = S, Se) has been investigated. Wein2K and BoltzTraP program packages are used to calculate the magnetic and transport characteristics of the spinels. While comparing the energies within the ferromagnetic and nonmagnetic states, the ferromagnetic state stability in the ground state is examined. The formation energy, phonon dispersion curve, and mechanical stability conditions help clarify the issue of stability in the cubic ferromagnetic phase. Poisson's and Pugh's ratios are employed to ensure the brittle characteristics. To explore the electronic properties, modified Becke and Johnson (mBJ) potential are utilized to investigate both spinels' direct narrow bandgap (spin up channel) nature. Chalcogenide's 2p produces the total magnetic moments- and rare-earth metals' f-states, which result in significant hybridization around the Fermi level. The computed total magnetic moment integer values and polarization are used to demonstrate spin polarisation. Finally, the Seebeck coefficient, thermal-to-electrical conductivity ratio, and power factor are used to evaluate thermoelectric properties.

Topology-insensitive axion mass in magnetic topological insulators

We study the axion in three-dimensional topological insulators with magnetic impurities under finite temperature. We find a stable antiferromagnetic ground state and ferromagnetic metastable state. In both magnetic states, the mass of the axion is found to be up to eV scale and it approaches zero near the phase boundary of the magnetic state. This result applies to both normal and topological insulator phases, i.e., the axion mass is insensitive to the topological states, and it will have a direct impact on the targeted mass range of particle axion dark matter in future experiments.

Induced Hyperfine Field in Doped Chalcopyrite Compounds Cu(In<sub>1-x</sub>A<sub>x</sub>)S<sub>2</sub> (A = V and Cr)

Hyperfine field and electronic states of doped chalcopyrite compounds Cu(In1-xAx)S2 with A = V and Cr are calculated by Korringa- Kohn-Rostoker Green’s function method, where x denotes the concentration of A atoms. The V and Cr doped compounds are ferromagnetically stable in terms of energy minimization and their electronic states are half metallic. The hyperfine fields in the stable ferromagnetic (FM) state are calculated with their valence and core contributions. In addition, site preference local magnetic moments are calculated for the FM and disordered spin moment (DSM) states. Density of states (DOS) exhibit the spintronic property of half metallicity. The local core and valence field polarizations are found in the doped chalcopyrite systems, where the s-orbital hybridization with the local d-shell is explained in terms of some exchange mechanisms. Dhaka Univ. J. Sci. 69(3): 149-153, 2022 (June)

Comprehensive study of ferromagnetic MgNd2X4 (X = S, Se) spinels for spintronic and solar cells device applications

Full potential LAPW + lo method is used for exploring electronic, structural and thermoelectric properties for MgNd2X4 (X = S, Se) spinels that are found to show ferromagnetic-semiconductor behaviour in the spinel structure. The investigated negative value of formation energy and positive value of phonon spectra computed using PBEsol GGA indicates the energetic and dynamical stability of the studied cubic ferromagnetic-semiconductors. We have used TB-mBJ potential functional for electronic and magnetic properties, which lead to a reliable account of electronic structure, demonstrating band occupancy in the spinels along with a clear explanation of density of states. The stability of ferromagnetic state in the studied materials is because of the exchange splitting of Nd cations based on p-d hybridization which is in accordance with the results obtained for electronic band structure and density of states. The exchange splitting of bands can be justified by the spin magnetic moment between anions and cations, and sharing of charge. The computed values of dielectric constant and their associated optical parameters are used to explain the optical active behaviour of the spinels under investigation; indicating that the two spinels studied in the present work are suitable for solar cells device applications. The calculation of thermoelectric properties is very useful for determining a material's potential use in waste energy recovery systems and many other innovative applications.

First-principles calculations to investigate electronic structures, ferromagnetic and optical properties of SnSe2 doped with double impurities

The electronic structures, ferromagnetic and optical properties of pure SnSe2, Fe doped SnSe2, Mo doped SnSe2 and (Fe, Mo) co-doped SnSe2 are studied by the first-principles calculations of the GGA + U methods. The calculation results indicate that the introduction of Fe and Mo atoms can induce total magnetic moments of 4 μB and 1.98 μB, respectively. However, there is a stable ferromagnetic state with ΔE value of about −538.7 meV for (Fe, Mo) co-doped SnSe2, and the ferromagnetic state is resulted from the powerful hybridisation of Fe:3d, Mo:4d and Se:4p orbitals. With the addition of transition metals Fe and Mo, the band gap is gradually reduced but the conductivity is increased. In addition, the addition of Fe and Mo increases the spectral value of the system in visible light, and the addition of Fe can make up for the deficiency of pure SnSe2 in infrared light absorption. Besides, the doping system has a low transmittance in the infrared region. In short, the Fe, Mo doped SnSe2 are helpful to make it to be excellent candidate material in ferromagnetic and photoelectricity fields.

First-principles study of In and Mn dopants on the magnetic and optical properties of 4H–SiC

By combining the GGA + U method, the magnetic and optical properties of (In, Mn) co-doped 4H–SiC and (In, 2Mn) co-doped 4H–SiC systems are calculated by first principles. The results show that the local magnetic moment of the (In, Mn) co-doped 4H–SiC system is 5.14 μB. And (In, 2Mn) co-doped 4H–SiC system can get the most stable ferromagnetic state, in which the energy difference △ EFM is 172.2 meV. The ferromagnetism of (In, 2Mn) co-doped 4H–SiC comes from the strong hybridization between the Si:2p orbitals, the C:2p orbitals and the Mn:3d orbitals near the dopant. In addition, the introduction of dopant atoms can reduce the band gap and improve conductivity. The doping system can weaken the maximum dielectric peak, thereby weakening the electromagnetic absorption ability of ϵ1(ω) in 4H–SiC. The doped system shows a red shift. And the doping system has lower transmittance in the infrared and visible regions. Our results show that doping 4H–SiC with In and Mn atoms is an effective method to modulate the magnetic and optical properties of 4H–SiC. Keywords: First principle, Magnetism, Optical properties, 4H–SiC.

Combined effect of strain and screw dislocation on the ferromagnetic behavior of ZnO nanowires

Owing to its excellent structural flexibility, a noteworthy strain adaptability was discovered from the screw dislocation located in zinc oxide (ZnO) nanowires (NWs). Based on density functional theory (DFT), the electronic structure and magnetic coupling mechanism of Zn vacancies (VZn) in this dislocation while sustaining inhomogeneous strain patterns were explored. The electronic structure analysis revealed that a double screw characteristic could be observed from the center of the dislocation, where O atoms were under 3-fold coordination. This was beneficial to the capture of numerous VZn. Meanwhile, the most stable configuration was obtained under a −2% strain, which enhanced the stability and interaction of VZn, allowing the couplings of VZn to form steady VZn pairs. A stable ferromagnetic (FM) state then originated from the p-p spin couplings of surrounding O-2p orbits. It was deduced that the long-range FM ordering could be regulated by the combined effect of strain and screw dislocation.

Systematic, First Principle Study of Ambient Temperature Ferromagnetism and Elastic Anisotropy of Cubic Ca0.75TM0.25S (TM = Mn, Co, and Ni) Ternary Alloys: Using mBJ Functional

Ab initio calculations are performed to investigate theoretically the structural stability, electronic, magnetic, and elastic properties of dilute magnetic semiconductors Ca0.75TM0.25S (TM = Mn, Co, and Ni). These materials crystallize in the ferromagnetic rock-salt phase and are made by doping the CaS binary semiconductor with transition metals at a fixed concentration. Calculations are performed using the full-potential linearized augmented plane wave method, plus the local orbital method (FP-LAPW+lo). The correlation exchanges potential and the structural properties are calculated using the generalized gradient approximation proposed by Perdew-Burk-Ernzerhof (PBE-GGA) and the electronic and magnetic properties are calculated using the Becke and Johnson modified local density approximation (mBJ–LDA). The comparison of curves giving energy as a function of volume in the fundamental state of the compounds in the ferromagnetic (FM), antiferromagnetic (AFM), and paramagnetic (PM) phases presented that the compounds are stable in the ferromagnetic phase. Analysis of the electronic properties showed that Ca0.75Mn0.25S, Ca0.75Co0.25S, and Ca0.75Ni0.25S are all ferromagnetic semiconductors. Various parameters like spin-exchange splittingΔx(d), crystal field energyΔECrystal, and exchange constants N0αand N0β have also confirmed a stable ferromagnetic state. The magnetic study revealed a strong contribution to the value of the total magnetic moment of the compounds, with low contributions coming from the non-magnetic atoms Ca and S. The Curie temperature values, calculated by the mean-field approximation, are 240.78 K, 228.79 K, and 150.31 K in the compounds containing Mn, Co, and Ni, respectively. The study of the mechanical properties of the host semiconductors CaS doped with transition metals, Mn, Co, and Ni, carried out at zero pressure has shown that all compounds are brittle and mechanically stable.

Tunable valley polarization, magnetic anisotropy and dipole moment for layered Janus 2H–VSSe with intrinsic room temperature ferromagnetism

Effects of strain, interlayer coupling and electric field on the valley polarization, magnetocrystalline anisotropy and dipole moment of layered Janus 2H–VSSe are systematically investigated by first-principles calculations. A unique V 3 d1 electronic configuration and strong electron coupling interaction guarantee the stable in-plane ferromagnetic ground states with Tc of 512 K. By considering spin-orbit coupling (SOC) and exchange interaction based on the effective Hamiltonian k•p model, a large valley splitting of 94.8 meV is observed, which is mainly contributed by the spontaneous magnetic exchange field and not SOC effect. Under various bi-axis strains, Janus 2H–VSSe monolayer still maintains intrinsic in-plane ferromagnetism, but exhibits tunable valley polarization and magnetocrystalline anisotropy, which are associated with the in-plane dx2-y2/dxy orbitals of V atoms. Importantly, stacking patterns can influence the spatial inversion symmetry and further alter the valley polarization for the layered Janus 2H–VSSe. Applied external electric-field can effectively control intrinsic built-in electric-field by charge redistribution in the vertical direction, which can remarkably change the dipole moments and slightly adjust the valley polarization. The layered Janus 2H–VSSe possesses intrinsic ferromagnetism, robust valley-contrasting physics and outfield-dependent dipole moment, making them competitive materials for practical applications in spin-valleytronics, optoelectronics and piezoelectric sensor.

Effect of hybridization on half metallic properties of some diluted chalcopyrites for spintronic applications

Based on the ab initio electronic structure calculations performed by Korring–Kohn–Rostoker method combined with the coherent potential approximation, the effect of transition metals impurities on the electronic states and magnetic properties of ZnXAs2 (X = Sn, Ge) chalcopyrites has been investigated. Electronic density of states, Curie temperature TC, ferromagnetic (FM), antiferromagnetic (AF) and spinglass-like (DLM) energies and their variation as well as crystal field splitting energy ΔCF and exchange interactions Δe and are all discussed in detail. The analysis of the densities of states of Zn(Sn, TM)As2 and Zn(Ge, TM)As2 shows that these compounds exhibit half-metallic character and high-spin ferromagnetic state. The importance of different exchange mechanisms like double exchange, ferromagnetic and antiferromagnetic super-exchange in Zn(Sn, TM)As2 and Zn(Ge, TM)As2 chalcopyrites is also discussed. The result as derived in this report shows that and doped ZnSnAs2 and ZnGeAs2 chalcopyrites exhibit a stable ferromagnetic half metallic state, whereas doping manifests antiferromagnetic and spinglass-like states. These results make Zn(Sn, TM)As2 and Zn(Ge, TM)As2 chalcopyrites useful for spintronic applications.

Use of density functional theory to investigate the optical and magnetic behaviours of Ge1-xMnxTe half-metallic ferromagnets

Ge1-xMnxTe-based IVVI ferromagnetic semiconductors are attractive due to their versatile material properties. In this study, we investigate the physical properties of Ge1-xMnxTe with xMn≤ 0.50 using density functional theory. The dominant exchange splitting caused by pd-hybridisation mediates ferromagnetism that is consistent with the stable ferromagnetic (FM) states, as observed using structural optimisations. The presence of holes due to the half-metallic character suggests that RKKY interactions stabilise FM states. The absorption edges lie in the infrared energy range and are influenced by the crystal symmetry, and the compounds exhibit strong absorption of visible and UV energies. The narrow band gaps extracted from the band structures and the Tauc plots show similar variations with the Mn content, and hence suggest applications in optoelectronic devices.

Density functional study on electronic structures and magnetic properties in (Cr, N) co-doped anatase TiO2

The electronic structures and magnetic properties of Cr-doped and (Cr, N) co-doped anatase TiO2 are investigated using first principles method. Both Cr-doped and (Cr, N) co-doped anatase TiO2 all exhibit ferromagnetic states. For Cr doped systems, the enhancement of ferromagism can be attributed to the Cr: 3d-O: 2p coupling chain formed by p-d hybridization between Cr and its surrounding O atoms. For the (Cr, N) co-doped TiO2 system, various configurations still showed very stable ferromagnetic state, which achieved our expectations. Our research provides a new way for the exploration of TiO2 in spintronics.