International Journal of Modern Physics B

A characteristic feature of long-range interacting systems is that they become trapped in a non-equilibrium and long-lived quasi-stationary state (QSS) during the early stages of their development. We present a comprehensive review of recent studies of the core-halo structure of QSSs, in the Hamiltonian mean-field model (HMF), which is a mean-field model of mutually coupled ferromagnetic XY spins located at a point, obtained by starting from various unsteady rectangular water-bag type initial phase-space distributions. The main result exposed in this review is that the core-halo structure can be described by the superposition of two independent Lynden–Bell distributions. We discuss the completeness of collisionless relaxation of this double Lynden–Bell distribution by using both of Lynden–Bell entropy and double Lynden–Bell entropy for the systems at low energies per particle.

The paper considers a static isotropic self-gravitating perfect gas in the presence of thermal radiation. The gravitational field is specified in terms of the radiation and gas pressures. Assuming that the thermodynamic internal energy is small compared with relativistic rest energy, it is shown that the gas pressure satisfies the Lane–Emden equation; the assumption of dominant intrinsic relativistic rest energy is satisfied by the hottest stars. Six-solutions of the Lane–Enden equation are obtained together with the corresponding gravitational fields. The basis for comparison is the singular solution I decaying like the inverse square of the radius, that is the leading term of the asymptotic solution V. Two semi-linear solutions are obtained using as variables nonlinear functions of the gas pressure, leading to nonlinear second-order differential equations that can be linearized; one solution II holds for small radius and leads to zero, finite or infinite central pressure, and the other solution III holds asymptomatically and exhibits pressure oscillations. The singular solution I for large radius is matched to a power series solution IV for small radius leading to a solution valid for all radii. The asymptotic solutions III and V: (i) coincide in their common domain of validity; (ii) can be truncated with good accuracy leading to the solution VI.

In this paper, we describe a novel reflective sandwiched three-port grating with two dielectric layers. The two-layer sandwiched grating can separate incident wave into the $\pm 1$ and the 0th-order with high-efficiency beam splitting and good splitting ratios for both transverse electric (TE) and transverse magnetic (TM) polarizations. The grating parameters can be optimized by using rigorous coupled-wave analysis (RCWA) with a special duty cycle of 0.6. With the optimized results, efficiencies more than 32% in the $\pm 1$st-orders and the 0th-order can be obtained. Furthermore, performance of the incident bandwidth and aspect ratio can be improved. Compared with conventional surface-relief grating, the grating with sandwiched structure is aimed at cleaning and protecting grating surface. The presented reflective two-layer sandwiched three-port grating would be put into practical applications for its beneficial performances.

We report here on the multiferroic properties of ZnO–BiFeO₃ (BiFeO₃ referred hereinafter as BFO) nanocomposite structures obtained by using a facile solution-based synthesis route. ZnO is found to grow in the form of well-crystallized and self-assembled dumbbell-like structures. BFO nanoparticles (NPs) are deposited onto ZnO nanodumbbells (NDs) to obtain ZnO–BFO heterostructures. The nanocomposites show prominent ferroelectric polarization hysteresis loop along with enhanced magnetization in comparison to pure BFO NPs. The ordered alignment of spins along with the suppression of Fe–O–Fe antiferromagnetic super-exchange interactions at the ZnO/BFO interface plausibly gives rise to observed multiferroic properties.

In this paper, we performed an ab initio calculation of the different properties of the full-Heusler alloy Ti₂VPb which is reported for the first time using the WIEN2k implementation of the full potential linearized augmented plane wave (FPLAPW) scheme. In order to study this compound for magneto-electronic applications we used the generalized gradient approximation (GGA) approximation for its mechanical properties but the MBJ-GGA to better investigate the electronic properties. Our results show that the Ti₂VPb compound exhibits half-metallicity at its equilibrium lattice 6.548 Å but a metallic character would occur with an expansion of its lattice parameters to 6.85 Å.

The electronic, thermoelectric, optical, and magnetic properties of the samarium aluminate (SmAlO₃) compound is studied using the spin-polarized full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). The exchange and correlation potential is treated with the generalized gradient approximation (GGA) and the Coulomb repulsion ($U=0.51$ Ry) has been calculated theoretically and was used for the GGA$+U$ based approximated electronic structures. Additionally, the modified Becke–Johnson (mBJ) potential was also utilized along with the GGA$+U$ approach for the calculation of the band gap. On the other hand, the optical properties were analyzed with the mBJ$+U$ results and the thermoelectric properties were explained on the basis of the electronic structures and density of states (DOS) with a thermoelectric efficiency of 0.66 at 300 K. The minimum reflectivity at 1.13 eV (which was equal to 1.097 $\mu$m) was found to be in agreement with the experimental results. Further refinements in the electronic structures were obtained by adding the spin–orbit coupling (SOC) interactions to the GGA$+U$ approach, which was then combined with the mBJ approximations. Hence, a conclusion using the combined mBJ$+U+$SOC study indicates that the SmAlO₃ compound is a potential candidate for both thermoelectric as well as magnetic devices.

The phenomenon of domain magnetic shielding by the magnetic sample of external and intrinsic magnetostatic field has been revealed. In this work, we investigate the possibility for detection of the shape and size of magnetic impurity based on the shape of magnetic domain configuration in magnetic film. We show that due to the influence of magnetostatic field of stripe domain structure in magnetic film on the magnetostatic field of magnetic impurity, one can determine the shape and size of this impurity.