Stability Of Ferromagnetic Phase Research Articles

Comprehensive DFT investigation of Cd-based spinel chalcogenides for spintronic and solar cells devices

In light of existing literature of stable ferromagnetic phase, the thermoelectric and optical behavior of the Cd-based spinel chalcogenides i.e. CdCr2X4, (X = S, Se, Te) were inspected and their structural and electronic characteristics were examined in terms of density functional theory calculations. The negative values of formation energy of said spinels were calculated to confirm their ferromagnetic phase stability. Optimization of band structure and calculations of density of states confirmed their ferromagnetic nature. For both channel, the band structure exhibited the semiconducting behavior. The exchange constants (N0α and N0β) were investigated with the help of exchange splitting energies, which were explored from the density of states. The splitting of 3d-states of Cr were explained on the basis of larger value of N0β as compared with N0α. Owing to the strong p-d hybridization indicated by N0β = −0.11, −0.12 and −0.15 and N0α = 0.14, 0.32 and 0.44 for CdCr2S4, CdCr2Se4 and CdCr2Te4, respectively, the necessary condition for ferromagnetic system is satisfied showing that exchange field dominates over the crystal field that induces the ferromagnetism in these spinels. Moreover the p-d hybridization was used to decrease the magnetic moment at Cr ions, by using a fraction of magnetic moment at non-magnetic sites. Further, optical characteristics were investigated in terms of photon energy 0–6 eV showing less dispersion of light and refractive index ranges up to 1–1.5 in visible region, thus suggesting spinels as potential candidates for opto-electronic applications. The thermoelectric performance observed in the temperature range of 200–600K which indicate positive Seebeck coefficients of ∼250 CdCr2S4, CdCr2Se4 while a negative Seebeck coefficients of −112 for CdCr2Te4 at room temperature. Further the power factors increased from S to Te as well as with increase of temperature which shows the potential of these chalcogens for thermoelectric power generators.

Computational insights in predicting structural, mechanical, electronic, magnetic and optical properties of EuAlO3 cubic-perovskite using FP-LAPW method

In this work, we have investigated structural, elastic, electronic, magnetic and optical properties of EuAlO3-cubic perovskite using FP-LAPW. Structural and elastic obtained results using GGA-PBEsol have shown the ferromagnetic phase stability of EuAlO3. The elastic constant and their related parameters such as Poisson’s ratio, Young modulus, shear modulus and Debye temperature have been estimated. Shear modulus and bulk modulus which have been calculated by Voigt, Reuss and Hill approximations have shown that EuAlO3 has a weak elastic anisotropy. This behavior has been confirmed by the analyses of 3D surface of the directional dependence of Young’s modulus, which is almost spherical with a small deformation. Both B/G ratioand Cauchy pressure show that EuAlO3 has a brittle nature. Spin polarized electronic properties, especially band structure and density of states curveshave been calculated by combiningGGA + U and TB-mBJ approaches. The obtained results have shown that EuAlO3adopt a half-metallic behavior. The obtained result of spin polarization, which is 100% at the Fermi level, has confirmed the half-metallic behavior of this compound. Furthermore, optical properties, including real and imaginary parts of the dielectric function, refractive index and extinction coefficient have been investigated.

Robustness in ferromagnetic phase stability, half‐metallic behavior and transport properties of cobalt‐based full‐Heuslers compounds: A first principles approach

AbstractHeusler alloys fill up the demanding gaps and becomes a point of prestige due to their interesting multi‐dimensional and remarkable applications in future technologies like spintronics and thermoelectrics. Self‐consistent ab‐initio calculations with highly precise spin‐polarized density functional theory associated with Boltzmann transport scheme have been perform to investigate the structural stability, mechanical, magneto‐electronic, thermo‐physical and thermoelectric transport properties of Co2VX (X = Sn, Sb) Heuslers. The equilibrium lattice parameters at the cost of structural optimizations are observed to agree with the available experimental data. The occurrence of perfect band occupation and interpretation of density of states through the modified version of Becke Johnson scheme delivers more precise and accurate results rather than GGA and GGA + U, possessing an indirect band gap of 1.12 eV and 1.34 eV in spin down channel of Co2VX (X = Sn, Sb) Heuslers respectively. Robustness of various elastic constants and its other associated mechanical constituents against external forces is checked to define the stability of these alloys. The transport parameters like Seebeck coefficient, electrical and thermal conductivity, power factor and zT have been put together to express their thermoelectric response. Conservative estimates of Seebeck coefficient and zT demonstrate its extending application stand in thermoelectric energy harvesting technologies. Furthermore complete and precise description of thermo‐physical behavior of the vital quantities like Debye temperature, thermal expansion, Grüneisen parameter and specific heat were examined to check its thermo‐dynamical stability against temperature and pressure variation.

Systematic study of ferromagnetic phase stability of Co-based Heusler materials with high figure of merit: Hunt for spintronics and thermoelectric applicability

The high throughput thermoelectric devices are considered a promising futuristic energy source to control global warming and realize the dream of green energy and a sustainable environment. In the present work, strict and highly accurate spin-polarized density functional theory combined with the Boltzmann transport scheme has been applied to extract the properties of Co2XAl (X = Zr, Nb, Hf) Heuslers. The mechanical stability appropriately prefers their cubic crystalline geometry with the ductile character of these alloys. The modified Becke–Johnson potential illustrates better results than GGA and GGA+U functionals. The band profile is found to be n-type (indirect bandgap) for Co2NbAl and p-type (direct bandgap) for Co2ZrAl and Co2HfAl Heuslers near the Fermi level. The preferably asymmetric density of states and structural optimization demonstrate the ferromagnetic character of these Heuslers. The formation and cohesive energy recommend that these alloys are thermodynamically stable. The Co2XAl (X = Zr, Nb, Hf) Heuslers deliver the significant value of the vital parameters like the Seebeck coefficient, zT, and power factor, which recommends the better thermoelectric response for practical applications. The improved stability, ductile behavior, durability, and rational zT should turn helpful in deciding the scalable potential of Co2XAl (X = Zr, Nb, Hf) materials for the design of long-lasting thermoelectric generators and flexible electronic devices.

Evidence of ferromagnetic ground state and strong spin phonon coupling in Zr2TiAl with bi-axial strain: first principles study

A detailed study on the inter-metallic alloy, Zr2TiAl, has been carried out using first principle electronic structure calculations. We found that a small value of bi-axial strain/stress cause a phase change from anti-ferromagnetic(AFM) to ferromagnetic(FM) with a structural transition from face center cubic (fcc) to body center tetragonal (bct). Calculated electronic band structures show that all strained structures are metallic in nature with Zr-d and Ti-d orbital dominated energy bands near the Fermi level(EF). The stability of FM phase is confirmed with phonon dispersion calculations by using density functional perturbation theory (DFPT). It has been observed that AFM state with both positive and negative bi-axial stress exhibits unstable modes while corresponding FM state shows no such instability. This clearly indicates the existence of large spin phonon coupling in this material.

Ab-initio DFT based investigation of double perovskite oxide Ba2CdOsO6 with cubic structure

Electronic structure, magnetic, mechanical and thermodynamic properties of perovskites oxide Ba2CdOsO6 have been calculated within well know density functional theory via full potential linearized augmented plane wave (FP-LAPW) method. The structural study discloses ferromagnetic phase stability with a magnetic moment equal to integer value of 2 μB. The spin polarized band structure and density of states present half-metallic nature for the compound. The mechanical stability has also been determined by the estimation of elastic constants. From the calculated elastic constants mechanical properties like Shear modulus (G), Youngs modulus (Y) Poisson ratio (ν), anisotropic factor (A) etc have been estimated. The calculated Pugh's ratio and Cauchy pressure both characterize this material as ductile. The effect of pressure and temperature on thermodynamic properties like heat capacity, thermal expansion, Grüneisen parameter and Debye temperature have been analyzed via quasi harmonic Debye model.

A combined DFT, DFT + U and mBJ investigation on electronic structure, magnetic, mechanical and thermodynamics of double perovskite Ba2ZnOsO6

First successful ab initio calculations on electronic structure, magnetic, elasto-mechanical and thermodynamic properties of cubic double perovskite oxide Ba2ZnOsO6 has been effectively calculated within density functional theory via full potential linearized augmented plane wave (FP-LAPW) method. The structural investigation exposes the ferromagnetic phase stability of the compound. The spin polarized electronic and magnetic properties were calculated within generalized gradient approximation (GGA), Hubbard approximation (GGA + U), mBJ (modified Becke-Johnson approximation). The electronic profile establishes half-metallic nature for the compound. The calculated total spin magnetic moment was found equal to 2 µB. The elastic constants have been calculated and used to predict mechanical stuffs like Shear modulus (G) Poisson ratio (ν) and anisotropic factor (A). The calculated B/G and Cauchy pressure (C12-C44) both characterize the material as brittle. The thermodynamic parameters like heat capacity and Debye temperature have also been predicted in the temperature range of 0 K–1000 K.

Ferromagnetic Phase Stability, Magnetic, Electronic, Elasto-Mechanical and Thermodynamic Properties of BaCmO3 Perovskite Oxide

The structural, electronic, elasto-mechanical and thermodynamic properties of cubic ABO3 perovskites BaCmO3 has been successfully calculated within density functional theory via full potential linearized augmented plane wave. The structural study divulges ferromagnetic stability for the compound. For the precise calculation of electronic and magnetic properties a generalized gradient approximation (GGA), and a Hubbard approximation (GGA + U), (modified Becke Johnson approximation) mBJ have been incorporated. The electronic study portrays the half-metallic nature for the compound in all the approximations. The calculated magnetic moment with different approximations was found to be large and with an integer value of 6 μb, this integer value of magnetic moment also proves the half-metallic nature for BaCmO3. The calculated elastic constants have been used to predict mechanical properties like the Young modulus (Y), the Shear modulus (G) and the Poisson ratio (ν). The calculated B/G and Cauchy pressure (C12-C44) present the brittle nature for BaCmO3. The thermodynamic parameters like heat capacity, thermal expansion, and Debye temperature have been calculated and examined in the temperature range of 0 K to 700 K and pressure between 0 GPa and 40 GPa. The melting temperature was also calculated and was found to be 1847 ± 300 K.

Insight into electronic structure, magnetic, mechanical and thermodynamic properties of double perovskite Ba2MgReO6: A first-principles investigation

In the present paper, we have investigated structural, electronic, magnetic, mechanical and thermodynamic properties of cubic double perovskite oxide Ba2MgReO6 within density functional theory via full potential linearized augmented plane wave (FP-LAPW) and quasi-harmonic Debye approximation. The structural study reveals ferromagnetic phase stability. The spin polarized electronic band and density of states (DOS) presents half-metallic nature, with spin up states as metallic and spin down states as semi-conducting. The total magnetic moment was found equal to 1 μB, with a major contribution from Re atoms. The calculated values of elastic constants properly follow the mechanical stability criteria. From elastic constant values the mechanical properties such as Bulks modulus (B), Shear modulus (G), Young's modulus (Y) and anisotropic factor (A) have been calculated. The calculated B/G and Cauchy pressure (C12-C44) both characterize the material as ductile. Furthermore, the thermodynamic parameters such as heat capacity, thermal expansion, Grüneisen parameter and Debye temperature have been predicted using Debye model.

Understanding Ferromagnetic Phase Stability, Electronic and Transport Properties of BaPaO3 and BaNpO3 from Ab-Initio Calculations

An extensive study of rare-earth perovskite BaPaO3 and BaNpO3 has been performed by first-principles tactics based on density functional theory (DFT), because the delocalized f-electrons play an important role in the band structure formation, to reveal their impact on the overall physical and chemical properties; it has turned out to be an interesting theme. Along with critical radii and thermoelectric properties, two different theories are employed to calculate the structural properties. The DFT and empirically calculated lattice constants are in rational accord with the experimental results. The critical radius calculations show that the BaPaO3 lattice has a smaller oxygen migration activation energy than the BaNpO3. In addition, we discuss the band profile and magnetic moments for these materials, which demonstrate the half-metallic ferromagnetism with a direct energy gap of 3.91 eV for BaPaO3 and an indirect gap of 3.79 eV for BaNpO3. More interestingly, the integral magnetic moments are in accordance with the Slater–Pauling rule.

Study of magnetic and optical properties of Zn1−xTMxTe (TM = Mn, Fe, Co, Ni) diluted magnetic semiconductors: First principle approach

We present structural, magnetic and optical characteristics of , calculated through Wien2k code, by using full potential linearized augmented plane wave (FP-LAPW) technique. The optimization of the crystal structures have been done to compare the ferromagnetic (FM) and antiferromagnetic (AFM) ground state energies, to elucidate the ferromagnetic phase stability, which further has been verified through the formation and cohesive energies. Moreover, the estimated Curie temperatures Tc have demonstrated above room temperature ferromagnetism (RTFM) in . The calculated electronic properties have depicted that Mn- and Co-doped ZnTe behave as ferromagnetic semiconductors, while half-metallic ferromagnetic behaviors are observed in Fe- and Ni-doped ZnTe. The presence of ferromagnetism is also demonstrated to be due to both the p–d and s–d hybridizations between the host lattice cations and TM impurities. The calculated band gaps and static real dielectric constants have been observed to vary according to Penn’s model. The evaluated band gaps lie in near visible and ultraviolet regions, which make these materials suitable for various important device applications in optoelectronic and spintronic.

Co spin state and magnetic structure in GdBaCo2O5+x and Fe doped compounds: A first principles study

GdBaCo2O5.5 exhibits impressive application potentials on giant magnetic resistance materials and solid oxide fuel cell cathodes, owing to its unique electrical and magnetic properties. In this article, stable magnetic-order structures of Co in GdBaCo2O5.5, Fe doped compounds, and GdBaCo2O5.25 with additional oxygen vacancy deficients, are investigated based on first principles calculations. Comparisons with reported experiments are also presented. It turns out that G type antiferromagnetic ordering is the most stable under ground state, and Co is high-spin state, which matches the observations of neutron diffraction and XAS spectrum. Calculated results show that the stability of ferromagnetic phase under low temperature will be enhanced by the introduction of Fe dopant, which is supported by the reported experiment. Moreover, additional oxygen vacancies caused by the valence alternation of Co ions are discussed. The magnetic moments of several Co cations closed to the additional vacancy are reduced. Besides, oxygen ions could be divided into 3 layers based on their stabilities. Oxygen vacancy formation energies within two layers are much lower, which facilitate the oxygen ion transfer along these layers. This result also fits the conclusion of reported molecular dynamic simulation well.

Origin of Suppression of Charge Ordering Transition in Nanocrystalline Ln0.5Ca0.5MnO3 (Ln = La, Nd, Pr) Ceramics

The bulk and nanocrystalline samples of half doped, rare earth, perovskite manganites, Ln0.5Ca0.5MnO3 (Ln = La, Nd, Pr) were investigated by X-ray diffraction and magnetic measurements at various temperatures to understand the origin of suppression of charge ordering transitions in nanocrystalline samples of these manganites. The controversial reports regarding the effect of crystallite size reduction on the unit cell volume has been resolved by studying these three manganites prepared by combustion synthesis method. As reported by earlier authors, reduction of the particle size to nanocrystalline range leads to suppression of charge ordering transition and stabilization of ferromagnetic phase at low temperatures. The unit cell volume is found to systematically increase for all the three manganites with decreasing particle size, which results in increased bandwidth and is responsible for suppression of charge ordering transition. Even through the crystal structure of both bulk and nanocrystalline samples is orthorhombic with space group Pnma, crystallite size reduction into nanocrystalline form affects the orthorhombic strain, lattice parameter, atomic coordinates, and unit cell volume. A comparative study for the La0.5Ca0.5MnO3 samples prepared by sol–gel route is also presented to show that the reduction of the unit cell volume with decreasing crystallite size is linked with nonstoichiometry of the samples, which can also lead to the suppression of the charge ordering transition and stabilization of ferromagnetic state in nanocrystalline form reported by some earlier authors. The role of inherent anisotropic strain in nanocrystalline samples on the magnetic state and phase transitions is also investigated.

A New Type of Bond‐Dilution Problem in a Ferromagnetic Insulator with a Fractional Random Coordination Number

AbstractThe ferromagnetic phase stability limits (or phase diagrams) of a quenched bond‐diluted spin‐ ½ transverse Ising ferromagnetic insulator with a fractional random coordination number are studied within the framework of the effective‐field theory with correlations. The changes of transition temperature and critical concentration with the topology of the network (or the averaged connectivity) are examined in the zero transverse field. The results obtained are compared with those available in the literature. The influences of transverse field on the critical frontiers are also obtained.

Magnetization in a quenched random-bond transverse Ising model with competing interactions.

Abstract The ferromagnetic-phase stability limit and magnetization of a quenched bond-mixed spin- 1 2 transverse Ising model (TIM) in an anisotropic simple square lattice are studied within the framework of an effective field theory considering both competing and non-competing interactions.

A quenched bond-mixed Ising model: Ferromagnetic phase stability limit

Within the framework of an effective field theory we discuss the ferromagnetic phase stability limit of a quenched bond-mixed spin fr12 Ising model in a simple cubic lattice. Whenever comparison is possible a satisfactory qualitative and to a certain extent quantitative agreement is observed.

Ferromagnetic phase breakdown of a quenched bond-mixed Ising model

Within the framework of an effective field theory beyond Mean Field Approximation, we discuss the ferromagnetic phase stability limit in the temperature-concentration space of a quenched bond-mixed spin- 1 2 Ising model in square lattice for both competing and noncompeting interactions J 1 and J 2. Quite reasonable results are obtained in both situations. In particular for the case of competing interactions, numerical estimates of the vanishing temperature critical bond concentrations are predicted for particular values of the ratio J 1 J 2 .