SPIN

The magnetic properties of anisotropic 3D Ising model on a cubic lattice are studied by Monte Carlo simulation. In particular, we have considered an extended 3D Ising model with spatially uniaxial anisotropic bond randomness on the simple cubic lattice parameterized by exchange interaction parameter $J$, anisotropy parameter $a$ and external longitudinal magnetic field $h$. The obtained numerical data clearly point out a second-order ferromagnetic-paramagnetic phase transition belonging in the same universality class with the 3D random Ising model at critical temperature $T_C$ that is strongly correlated to $a$ and $h$. Especially, in the limit, $a\to 0$, the spin ½ cubic lattice becomes a collection of noncorrelated Ising chains, whereas in the other limit, $a^{-1}\to 0$, the system becomes a stack of noncorrelated Ising square lattice.

We report on the effect of Carbon insertion on the microstructure and magnetic properties of nanocrystalline Pr₂Co₇C_x($x\le 1$). The Pr₂Co₇C_x were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and physical property measurement system (PPMS9) Quantum Design. Mean field theory was utilized to depict the temperature dependence of magnetization and deduce the exchange interactions. The approach to saturation magnetization was as well used. The results were interpreted in the framework of random magnetic anisotropy model. From such analysis, some fundamental parameters were extracted.

A model for lateral-type refracting-facet spin-photodiodes based on ferromagnetic metal-insulator-semiconductor (FM-I-S) junctions is described. The model utilizes spin and charge drift-diffusion equations and spin-dependent tunneling equations which are simultaneously solved numerically in order to obtain a self-consistent solution. The model is used to analyze and optimize the refracting-facet spin-photodiode structure. The relation between the active layer thickness and the effective lifetime of photo-generated electrons is investigated. Results show that the optimum active layer thickness depends on both effective lifetimes of photo-generated electrons and spins. The influence of empty density-of-state of ferromangetic metals is also explored.

We review the formulation of gauge fields in terms of the frame of reference as well as the space in which the frame is defined. We highlighted some recent applications of gauge physics in the momentum space — in the modern fields of the spin Hall effect, the magnon Hall, the optical Magnus and the graphene valley Hall. General procedures of gauge transformation which lead to the construction of the gauge curvature and the equations of motion (EOM) are outlined. Central to this review is our intention to illustrate the impact of gauge physics on the past and future development of many new research fields emerging out of condensed matter physics, particularly in quantum nanosciences and nanoelectronics.

This work presents ab initio study of the structural, electronic, magnetic and mechanical properties of Fe₂NiAl${}_{1-x}$Ga_x Heusler compounds with variable concentrations ($x=0$, $x=0.25$, $x=0.50$, $x=0.75$ and $x=1$) of Ga. Calculations have performed using the full-potential linearized augmented plane waves (FP-LAPW) method within generalized gradient approximation Perdew–Burke–Ernzerhof (GGA-PBE) formalism in order to describe the exchange–correlation potential. The obtained results showed that the equilibrium parameter values are in good agreement with the available experimental results. In the study of the electronic properties, band structure analysis indicated that all of our compounds have metallic behavior. The calculated total magnetic moments of our Heusler alloys are in line with the Slater–Pauling rule, and they agreed with the results of previous studies. For mechanical properties, shear modulus, Young’s modulus, elastic constants, Poisson’s ratio and shear anisotropy factor have studied. Their obtained values reveal that these compounds are mechanically and dynamically stable.

In this study, we report the electronic structure properties of SmFe₂ and HoCo₂ binary Laves phase compounds using the density functional theory (DFT) method. We treated the exchange correlation potential with generalized gradient approximation (GGA); in addition, GGA+U (U: Hubbard correction) calculations were applied to describe the correlation effects. At the equilibrium state, the lattice parameter $a_0$ is found in favorable agreement with the available data. We also treated the magnetic properties of SmFe₂ and HoCo₂, respectively; it is shown that the magnetic moment values of Sm and Ho atoms are larger than those of Fe and Ho elements. We note that the GGA with Hubbard correction (U) provides the best description of our systems. We also illustrated the band structures and total and partial densities of states (DOS) of the rare earth-4f (Sm and Ho) and transition metals-3d (Fe and Co) orbitals. For both approximations used, the SmFe₂ and HoCo₂ binary compounds have a metallic character at the Fermi level. This investigation shows the importance of the treatment of correlated electrons for a clear and accurate description of these binary compounds of the Laves phases family.

Lead magnesium tungsten titanate PbMg${}_{1∕3}$ Ti${}_{1∕3}$W${}_{1∕3}$O₃ was prepared by adopting a high-temperature solid-state reaction method. The sample has tetragonal crystal structure having average crystallite size 45.1325nm calculated using Scherer’s relation and the average grain size is about 40nm from Scanning Electron Microscope (SEM) measurement. Measurements of dielectric permittivity (${\epsilon }_r$) and loss ($\text{tan}\delta$) have been investigated, both as a function of frequency (1kHz to 5MHz) and temperature (25–$500^{°}$C) and the results showed the presence of interfacial polarization of the material. The dielectric spectra with frequency and temperature suggest that the prepared sample is semiconducting in nature following the NTCR behavior. The complex impedance results showed the contribution of grain and grain boundaries in the conduction mechanism. The activation energies were determined from the ac conductivity data in the temperature ranges of 200–$350^{°}$C and 360–$500^{°}$C. It has been observed that with the rise of frequency and temperature, the activation energy increases in the sample. The greater value of the activation energy always supports the conduction mechanism due to hopping of the charge carriers. The semicircular arcs of Cole–Cole plots confirm that the sample is semiconducting in nature which supports our dielectric results.

The first-principles approach based on density functional theory (DFT) and the full-potential linearized augmented plane-wave method were employed to investigate the structural, elastic, electronic and magnetic properties of Na$X$NO ($X=\mathrm{\text{Ca}}$, Sr and Ba) quaternary half-Heusler alloys. The generalized gradient approximation (GGA) as parameterized by Perdew, Burke and Ernzerhof (PBE) and the modified Becke–Johnson exchange potential were used. As far as we know, we present our results which for the first time quantitatively account for the electronic structures and magnetic properties of Na$X$NO ($X=\mathrm{\text{Ca}}$, Sr and Ba) quaternary half-Heusler alloys. From the total energy calculation using three possible atomic configurations ($\alpha$, $\beta$ and $\gamma$), it is found that the Na$X$NO ($X=\mathrm{\text{Ca}}$, Sr and Ba) quaternary half-Heusler alloys are more stable in the ferromagnetic $\gamma$-phase. From our estimated elastic constants $C_{ij}$, it is found that all the considered Heusler alloys are mechanically stable in the $\gamma$-phase. We have also investigated the robustness of the half-metallicity with respect to the variation of lattice constants in these alloys. We have found that these alloys are half-metallic ferromagnets (HMFs) with a magnetic moment of 2${\mu }_B$ per formula unit at their equilibrium volumes. The spin-polarized electronic band structure and density of states of these quaternary half-Heusler alloys calculated by GGA (mBJ-GGA) show that the minority spin channels have metallic nature and the majority spin channels have a semiconductor character with half-metallic gaps of 0.49eV (2.17eV), 0.72eV (2.28eV) and 0.96eV (2.22eV) for NaCaNO, NaSrNO and NaBaNO quaternary half-Heusler alloys, respectively. Analysis of the density of states and the spin charge density of these quaternary alloys indicates that their magnetic moments mainly originate from the strong spin-polarization of 2$p$ states of N atoms and O atoms.

Double perovskites are usually strongly correlated electronic systems that offer many multifunctional properties and are most commonly formed in the monoclinic crystal phase. In this study, we used a first-principles DFT approach in studying the optical and magnetic aspects of Ba₂MMoO₆ ($\mathrm{\text{M}}=\mathrm{\text{Mn}}$, Fe) double perovskite structures in a new monoclinic phase in both their pure and oxygen-deficient form and compared it to their natural cubic phase. The structural parameters of our structures were consistent with the available experimental data of the similar Ca₂MMoO₆ compounds. The optical analysis suggests a high dielectric function for both compounds in their pure and defected state. The addition of defects increases the absorption of photons near the visible spectra. We also found the structures to be half-metallic, with a reduction of magnetic strength and half-metallic gaps when oxygen defects are added to the structure. These features suggest a possible application in the optoelectronics and spintronics industry, even when the crystal structures have oxygen vacancies.