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In this work, we will investigate structural, electronic, magnetic, and thermodynamic properties using density functional theory (DFT) and the quasi-harmonic Debye model. We consider ferromagnetic (FM) and non-magnetic (NM) states for L2₁ and Hg₂CuTi-type crystal structures. The best stability is obtained for ferromagnetic Rh₂MnGa in a Cu₂MnAl structure with a lattice parameter of 6.07 Å and a total magnetic moment of 4.11${\mu }_B$. The compressive strain range from $-6$% to $+4$% tensile strain maintains the ferromagnetic nature and enhances the magnetic moment up to 4.39${\mu }_B$. The formation energy confirms the inherent stability of Rh₂MnGa. Other important thermodynamic parameters such as the expansion coefficient ($\alpha$), heat capacity ($C_V$), Debye temperature (${\theta }_D$) and Grüneisen constant ($\gamma$) are also estimated in this work.

We consider a two-dimensional Ginzburg–Landau model for superconductors which exhibit ferromagnetic ordering in the superconducting phase, introduced by physicists to describe unconventional p-wave superconductors. In this model the magnetic field is directly coupled to a vector-valued order parameter in the energy functional. We show that one effect of spin coupling is to increase the second critical field H_c2, the value of the applied magnetic field at which superconductivity is lost in the bulk. Indeed, when the spin coupling is strong we show that the upper critical field is no longer present, confirming predictions in the physics literature. We treat the energy density as a measure, and show that the order parameter converges (as the Ginzburg–Landau parameter κ→∞) in an average sense to a constant determined by the average energy.

As a contribution to the study of the Hartree–Fock theory, we prove rigorously that the Hartree–Fock approximation to the ground state of the d-dimensional Hubbard model leads to saturated ferromagnetism when the particle density (more precisely, the chemical potential μ) is small and the coupling constant U is large, but finite. This ferromagnetism contradicts the known fact that there is no magnetization at low density, for any U, and thus shows that HF theory is wrong in this case. As in the usual Hartree–Fock theory, we restrict attention to Slater determinants that are eigenvectors of the z-component of the total spin, 𝕊_z = ∑_x n_x,↑ - n_x,↓, and we find that the choice 2𝕊_z = N = particle number gives the lowest energy at fixed 0 < μ < 4d.

The one-dimensional Sznajd model "united we stand, divided well fall" is generalized to the square lattice with similar fixed points. Only in two of the variants are the distribution of equilibration times roughly log-normal. Probabilistic generalizations destroyed the "dictatorial" fixed points.

We demonstrate enhanced ferromagnetism in copper doped two-dimensional GaN monolayer (GaN-ML). Our first principle calculation based on density functional theory predicted that nonmagnetic Cu-dopant with concentration of 6.25% to be ferromagnetic (FM) in 2D GaN layer which carries a magnetic moment of 2.0 μ_B per Cu atom and it is found to be long range magnetic coupling among the Cu-dopant. The Cu-dopant in 2D GaN-ML which can be explained in terms of p-d hybridization at Curie temperature and this dopant prefer the FM behavior in 2D GaN layer. Hence Cu doped 2D GaN layer shows strong magnetic properties so that it is a promising material in the field of spintronics.

We describe recent results concerning the compatibility of the Lifshitz theory of dispersion forces with thermodynamics. It is shown that for ferromagnetic metals described by the plasma model and for ferromagnetic dielectrics with omitted dc conductivity the Lifshitz theory satisfies the Nernst heat theorem. At the same time, for magnetic metals described by the Drude model and for ferromagnetic dielectrics with account of dc conductivity the Nernst heat theorem is violated.

The main equations of the theory of superconductivity in non-adiabatic systems with ferromagnetic arrangement of spins of impurity atoms are derived. The influence of non-adiabaticity on the temperature of superconducting transition T_C as well as on the critical concentration of impurity is also studied. The behavior of the temperature of magnetic arrangement of spins T_k as function of concentration of impurity c in the superconducting state for the non-adiabatic systems is investigated as well. The phase diagram (T, c) is built and it is proved that the effects of non-adiabaticity favor a raise in the field with coexistence of superconductivity and ferromagnetism.

Rapid developments in material research of metallic ferromagnetic (III,Mn)V semiconductors over the past few years have brought a much better understanding of these complex materials. We review here some of the main developments and current understanding of the bulk properties of these systems within the metallic regime, focusing principally on the magneto-transport and magneto-optical properties. Although several theoretical approaches are reviewed, the bulk of the review uses the effective Hamiltonian approach, which has proven useful in describing many of these properties namely in (Ga,Mn)As and (In,Mn)As. The model assumes a ferromagnetic coupling between Mn d-shell local moments mediated by holes in the semiconductor valence band.

If the condition for magnetic nesting is fulfilled for the electron dispersion law with spin σ along a certain preferential direction n, ferromagnetism and the inhomogeneous superconducting state can coexist up to very high magnetization I. This fact was used to explain the coexistence of ferromagnetism and superconductivity for layered cuprates of the RuSr₂GdCu₂O₈ type, which possess a finite, though rather high critical magnetization, because the conditions for magnetic nesting are fulfilled only approximately.

The magnetization behaviors of two manganite oxide systems, La_0.7-xLn_xPb_0.3MnO₃ (Ln=PrandSm), have been synthesized. The replacement of La ions by Pr or Sm results in a considerable decrease in the ferromagnetic ordering temperature T_C and clearly irreversible behavior in the zero-field-cooling-field-cooling curve at a low applied field, showing a short-range spin order phase. These facts are in agreement with the smaller ionic radii of Pr (0.130 nm) and Sm (0.124 nm) ions in contrast to La ion (0.136 nm), and the corresponding larger distortion of perovskite structures. The saturation magnetization M_S decreases as Sm content increases relative to the increase of M_S as Pr content increases. This can be interpreted in terms of the competition between suppression of ferromagnetism due to structure tuning induced by the small ionic radius of the interpolated cations into the La-site and the increase of ferromagnetically interacting spins due to the introduction of magnetic Pr or Sm ions with f-shell electrons.

We present magnetic measurements on iron (Fe) nanoparticles in the size range 10–30 nm produced by the Inert Gas Condensation process (IGC). Structural characterization studies show the presence of a core/shell structure, where the core is bcc Fe while the surface layer is Fe-oxide. Analysis of the magnetic measurements shows that the nanoparticles display very large uniaxial anisotropy, K_eff≈3 - 4 × 106 erg/cc. The observed room temperature coercivities lie in the range ≈600 – 973Oe, much larger than those expected from the Stoner–Wohlfarth model using the bulk iron anisotropy. It can be inferred from the coercivity variation with the particle size that there is a general trend of the coercivity increasing with size, culminating finally in a decrease for high sizes (30 nm) possibly due to the onset of non-coherent magnetization reversal processes.

Nanocrystalline samples of Zn_1-xMn_xO (x = 0.0, 0.01, 0.02, 0.1 and 0.2) were synthesized by solid state reaction and characterized by X-ray diffraction and electron paramagnetic resonance (EPR) at room temperature. EPR studies showed an evidence of ferromagnetism above room temperature.

Ferromagnetism (FM) at room temperature in nano ZnO:Mn is closely monitored here for very low concentration of Mn, as there are conflicting reports on FM, in the uniformly doped system.

The electronic structure and ferromagnetism of Sn₂Co₂O₈ and Sn₂Co₂O₇ have been investigated based on the first-principles plane-wave pseudopotential method within the generalized gradient approximation. The calculated results reveal that the oxygen vacancy plays an important role in the electronic structure and ferromagnetism. The Sn₂Co₂O₈ shows half-metallic behavior, but by introducing single oxygen vacancy, the half-metallic transits to metallic behavior. At the same time, the spin magnetic moment of every Co atom and the total magnetic moment change greatly. For Sn₂Co₂O₈ and Sn₂Co₂O₇, the total spin magnetic moments are 1.99 and 3.49 u_B, respectively.

First-principles total energy calculations have been performed using full potential linear-augmented-plane-wave method within the framework of density functional theory to study the structural, electronic, magnetic and optical properties of the Pb_1-xEu_x Se and Pb_1-xEu_xTe(0 ≤ x ≤1) alloys in the ferromagnetic (FM) ordering. The calculations have been extended to treat the strongly localized f electrons of Eu atom by the self-interaction correction (SIC) approach. For structural optimization, the Wu and Cohen generalized gradient approximation (GGA) functional has been used, whereas for calculating electronic properties, the GGA parameterization scheme formulated by Engel and Vosko (EV) has also been utilized. It has been observed that the use of experimental value of Coulomb parameter (U_f-expt.) within the SIC does not yield an accurate EuSe and EuTe energy band structure. The improvement in the electronic band structures of nonmagnetic PbSe/PbTe and ferromagnetic EuSe/EuTe have been achieved by considering the effects of spin–orbit coupling for Pb atoms, by a suitable choice of U and by treating the U values for Eu atom's f and d electrons as parameters. The electronic and optical properties of FM Pb_1-xEu_xSe in agreement with experiments can be achieved by combining EV GGA with a Hubbard U < U_f-expt., however, a stronger and stable AFM coupling in EuTe leaves the above scheme unable to provide good electronic structure of FM Pb_1-xEu_xTe. In case of Pb_1-xEu_xSe the nonlinear behaviour of electronic structure is reflected in the optical properties of Eu-doped PbSe that have been studied in terms of incident photons' energy dependent complex dielectric function.

La-doped and Cu-doped ZnO nanowires have been prepared to compare the substitution effect on the microstructural and magnetic properties. The XRD patterns of both compositions with single diffraction peak (002) show the same wurtzite hexagonal structure. The growth rate of the ZnO nanowires were enhanced by Cu doping, which were different from the suppression of growth rate by La doping. Room temperature ferromagnetism is observed for all ZnO, Cu-doped ZnO and La-doped ZnO nanowires. The saturation magnetizations are 0.102, 0.232 and 0.04 emu/g for ZnO, Cu-doped ZnO and La-doped ZnO nanowires, respectively. The results showed that the ferromagnetism is restrained by Cu doping, but enhanced by the La doping.

Inspired from the connection between Lie symmetries and two-dimensional materials, we propose a new statistical lattice model based on a double hexagonal structure appearing in the G₂ symmetry. We first construct an Ising-1/2 model, with spin values σ = ±1, exhibiting such a symmetry. The corresponding ground state shows the ferromagnetic, the antiferromagnetic, the partial ferrimagnetic and the topological ferrimagnetic phases depending on the exchange couplings. Then, we examine the phase diagrams and the magnetization using the mean field approximation (MFA). Among others, it has been suggested that the present model could be localized between systems involving the triangular and the single hexagonal lattice geometries.

In this paper, ZnO nanoparticles doped with varying amount of Co content (i.e., 0, 2, 4, 6, 8, and 10 at.%) have been prepared by wet chemical route. X-ray diffraction (XRD) results reveal the successful substitution of Co²⁺ ions on to sites of Zn²⁺ ions without forming any secondary phase. Furthermore, a linear increase in d-spacing of the ZnO lattice is found with the increase in Co content. SEM images demonstrate the formation of homogeneously distributed spherical nanoparticles with average size of 50–70 nm. It is observed from optical investigations that band gap energy of ZnO nanoparticles significantly decreased with the increase in Co doping level. Interestingly, it is found that the high Co dopant concentration can lead to room temperature ferromagnetism in ZnO nanoparticles.

In this paper, we report structural parameters, magnetic ordering and the electronic structure of the tetragonal and orthorhombic ternary iron arsenide compound ${\mathrm{\text{BaFe}}}_2{\mathrm{\text{As}}}_2$. Ab initio calculations are performed by the means of full-potential linearized augmented plane waves plus local orbitals method for both spin states. The local spin density plus Hubbard potential ($\mathrm{\text{LSDA}}+U$) and generalized gradient plus Hubbard potential ($\mathrm{\text{GGA}}+U$) approximations are used to treat the exchange and correlation potentials. The results mainly show that orthorhombic ${\mathrm{\text{BaFe}}}_2{\mathrm{\text{As}}}_2$ compound has an antiferromagnetic spin ordering. Both spin-up and spin-down polarizations are considered to investigate the band structure, density of states and electron charge density. High density of states population at the Fermi level reveals metallic character of this material. The magnetism property arises essentially from the $3d$ orbital of iron atom.

In order to promote suitable material to be used in spintronics devices, this study purposes to evaluate the magnetic properties of the titanium and vanadium-doped zinc-blende ZnO from first-principles. The calculations of these properties are based on the Korringa–Kohn–Rostoker (KKR) method combined with the coherent potential approximation (CPA), using the local density approximation (LDA). We have calculated and discussed the density of states (DOSs) in the energy phase diagrams for different concentration values, of the dopants. We have also investigated the magnetic and half-metallic properties of this doped compound. Additionally, we showed the mechanism of the exchange coupling interaction. Finally, we estimated and studied the Curie temperature for different concentrations.