Journal of Progress in Physics of Applied Materials
Volume:1 Issue: 1, Dec 2021

Generating spin current by thermal gradient is referred to as Spin caloritronics. Spin caloritronics is an emerging new subfield of condensed matter physics concerned with coupled spin, charge, and energy transport in small structures and devices. In this paper, thermally induced spin transport in a magnetized zigzag graphene nanoribbon is explored. Using non-equilibrium Green’s function (NEGF) method in a tight-binding model, a temperature gradient applied between the left and right nonmagnetic electrodes, as thermal reservoirs in a magnetized zigzag graphene nanoribbon model junction so that the flowing of the up-spin and down-spin currents in the opposite directions can be induced which may be modulated by tuning of the back gate voltage. Furthermore, some thermoelectric properties of the junction, such as the spin-dependent Seebeck effect, electrical conductance, electron thermal conductance, and thermoelectric efficiency (ZT) of the model evaluated. Our calculations for the thermoelectric properties of the magnetized zigzag graphene nanoribbon indicate that for the zigzag edge graphene nanoribbon, the spin-dependent ZT is greater than the ZT of the electric charge. This means that the zigzag edge graphene nanoribbons are appropriate for spin thermal transport applications.

In this study, Magnesium Fluoride (MgF2) and Zinc Sulfide (ZnS) multi-layer antireflection coatings were prepared using Glancing Angle Deposition (GLAD) technique. MgF2 and ZnS materials have been coated in a Hind - Hivac coating unit (model 15F) on glass substrates. Antireflection coatings were prepared at different oblique incident flux angles (α = 40°, 65°,70°, 80°) by the thermal evaporation method. The Grazing incidence X-ray diffraction (GIXRD)analysis indicated that the thin films coated at different incident angles were crystallized in a single phase with an orthorhombic structure. The XRD results showed improvement of the film crystallinity upon grain size increment. Optical properties were investigated throughout the measurement of transmission spectra and refractive index and extinction in the visible region. The refractive index of films decreased from 2.8 to 1.66 as the flux angle increased from 40° to 80°. The extinction coefficient of films increased from 0.03849 to 0.05997 as the flux angle increased from 40° to 80°.

Today, there is a great request for radiation detection in medical and industrial fields. Zinc oxide (ZnO) and cadmium tungstate (CWO) are two types of scintillator perspective due to their useful features such as high density, large Z, and efficient scintillation output. In this study, ZnO and CWO nanopowders were synthesized by the simple sol-gel method, and ZnO and CWO films were prepared by spin coating technique on glass substrates. Samples were characterized by X-ray diffraction, transmission electron microscopy, and X-ray induced luminescence measurements. XRD analysis showed that ZnO and CWO powders were well synthesized with wurtzite and monoclinic wolframite structures, respectively. It was observed that the particle diameters for ZnO and CWO nanopowders are 22 and 100 nm, respectively. The scintillation response of samples was measured using a 241Am alpha source. Compared to ZnO, CWO nanopowders showed prominent luminescence properties with higher radiation sensitivity for applications in fields of radiation detection.

CuFe2O4 ferrite was synthesized by citrate precursor and then calcined at 800, 900, and 1000 °C. Structural properties showed that the X-ray diffraction patterns of the samples could be easily indexed to tetragonal CuFe2O4 ferrite with the spatial group the I 41/AMD. As the calcination temperature increased, the larger Cu2+ ion at the tetragonal site substituted the smaller Fe3+ ion at the octahedral site. The half-width of X-ray diffraction peaks can be affected by several factors such as instrumentation, crystallite size, and lattice microstrain broadening. The results of crystallite size and Microstrain estimated by different methods for the samples show that the Size-strain Plot method is more accurate, the value of R2 is close to 1 and all data points touch the fitting line better than other methods. The results showed that the increase in crystal size with calcination temperature could be mainly attributed to the increase of stretching microstrain.

In this paper, plasmon frequency manipulation using an external electric field was investigated. Using an external electric field with the right intensity can change the density of charge carriers in materials such as metals and semiconductors. This phenomenon can be used to design a tunable multi-range radiation detector. The density distribution formula of electric charge carriers is proposed as a function of the external electric field, dimension, initial density, and temperature. The validity of this formula was tested by comparing it with the Maxwell distribution function. The use of the formula on the formation of a hot point on the gp120-CD4 connection of HIV-1 and host cells was considered as a practical example. Finally, the effects of Johnson thermal noise and shot Coulomb noise are calculated to accurately determine the external electric field required.

In this research, silica (SiO2) and SiO2@Ag core-shell nanoparticles were synthesized by the co-precipitation method in the presence of ammonia as a reducing agent. First, the effect of different concentrations of tetraethyl orthosilicate (TEOS) as a precursor on the structural and optical properties of silica nanoparticles (SiO2) was investigated. Then, using this optimized concentration of TEOS, silica nanoparticles with silver shell were prepared by two methods (a) in the absence and (b) in presence of APTES (3-Aminopropyl triethoxysilane). The properties of SiO2@Ag core-shell nanoparticles prepared by two methods were compared and the best method was determined. For the synthesis of Ag nanoparticles, silver nitrate (AgNO3) and sodium borohydride (NaBH4) as reducing agents were used. To functionalize the surface of silica nanoparticles, 3-Aminopropyl-triethoxysilane (APTES) was added to the AgNO3 solution with polyvinyl-pyrrolidone (PVP) as a dispersant. The structural properties of silica and silica-silver core-shell nanoparticles were investigated by XRD and TEM. The average size of a silver single crystal in the core shells prepared by the two methods is about 25 nm and 14 nm, respectively. The optical absorption and bandgap were calculated for silica and SiO2@Ag core-shell nanoparticles. The results indicated that with increasing the concentration of TEOS precursor, the optical absorption of silica nanoparticles increased and their optical band gap reduced from 4.22 eV to 3.55 eV.

In this study, the magnetocaloric effect and magnetic properties of La0.6-xGdxSr0.4MnO3 (x= 0-0.1) samples (with the R-3c space group crystalize in rhombohedral structure) synthesized by the Sol-gel method is presented here. The aim of the study is the investigation of the Landau theory and universal curve approach applied to the magnetic entropy change of La0.6-xGdxSr0.4MnO3 (x= 0-0.1) compounds. A universal curve is an important tool that allows us to compare the performance quality of different materials during measurements, regardless of their nature, processing, or experimental settings. Thermodynamic models were used to calculate the MCE. Theoretical and experimental data -∆SM (T) are well-matched in the compounds. The study of the universal curve and Landau theory showed that the nature of the transition is the second-order ferromagnetic (FM) -paramagnetic (PM) magnetic phase transition. From an application point of view, theoretical research confirmed that compounds containing Gd in the La site can be used for magnetic refrigeration technology.

In this article, the effect of input current frequency on the induction heating process was investigated using a numerical method. We used a 2D finite element method (FlexPDE package) to solve the governing equations in combination with the boundary conditions. The obtained computational results show that this parameter has a great effect on the spatial distribution and the amount of heat produced in different parts of the induction heating system. For all workpiece thicknesses, the amount of heat generated in the workpiece and the RF coil decreases with increasing frequency. Also, changes in driving frequency can shift the location of the maximum point of energy production along the outer surface of the workpiece sidewall. In low frequencies, the maximum amount of heat is located at the middle portions of the outer surface of the workpiece wall, and by frequency increasing, it is shifted toward the two corners of the workpiece surface. These results will help us to select a proper frequency range for different applications of induction heating during material processing.

The present study investigated the cadmium-cobalt ferrite nanoparticles doped with chromium and ytterbium ions synthesized using the hydrothermal method. We analysed the samples by X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), and vibrating Sample Magnetometer devices (VSM). XRD confirmed the formation of an almost pure spinel structure. FESEM-obtained micrographs showed spherical shapes for nanoparticles and by using ImageJ software, an average particle size of about 40 nm was obtained. The saturation magnetization, the remnant magnetization, and the coercivity field were estimated using the hysteresis loop of the samples. The maximum coercivity field (815 Oe )was obtained in the sample doped with ytterbium. This could be due to enhancing the spin-orbit coupling and magnetocrystalline anisotropy constant of the cadmium-cobalt ferrite sample with ytterbium doping. The saturation magnetization decreased with the doping of both ions due to the lower magnetic moment of the doped ions compared to the Fe ion.

We numerically study the propagation of electromagnetic waves in Pascal plasma photonic crystals. For this purpose, the transfer matrix method is used. This method is based on defining multiple matrices for moving waves in interfaces and layers. Other methods such as finite difference time range can also be used, but are more suitable for higher-dimensional photonic crystals. We investigate the effect of dielectric layer refractive index, plasma electron density, total system length, wavelength angle, and the number of photon crystal layers on the transfer coefficient. A pseudo-code to create the Pascal multilayer is also presented. Finally, we describe the properties of the photonic bandgap, including position and width, because the parameters mentioned are different. We showed that as the refractive index n1 increases, the position of the gaps alternates redshifted and blueshifted (ie, decreasing and increasing the frequency and energy of the photon). Also, with increasing the refractive index n1, the width of the gaps decreased and increased. As the collision angle θ0 grew, the transmission edge blueshifted.

In this study, AM60 magnesium alloy surface modification was performed by electron beam irradiation at different energy densities of 3, 5, and 8 J/cm2 and a pulse duration of 2-4 μs for RITM installation and 100 μs for SOLO installation. Then the surface characteristics were analyzed and the process parameters were optimized based on microscopic images with scanning electron microscopy. The element magnesium, the intermetallic phase of Al-Mn and Mg-Al (Mg17Al12) were observed on the microstructure of all samples. It is significant that due to oxidation, the MgO phase was observed in AM60 alloy which was removed by pulsed electron beam irradiation (PEBI). This technique generally caused the percentage of the AlMn phase to be lower than the raw sample and even at the energy level of 8 j/cm2, the AlMn phase was ignored. However, the percentage of Mg17Al12 phase increased significantly after PEBI and this phase changed from block to point mode and spread throughout the material. It was found that with PEBI the surface characteristic changes and among the three levels of 33, 5, and 8 J/cm2, 5 J/cm2 has the lowest number of cracks and the shortest crack length.

WS2 was successfully synthesized by the hydrothermal method under various liquid nitrogen and microwave treatments. X-ray diffraction (XRD) analysis showed the presence of multiple WS2 phases, of which hexagonal was the dominant phase. The morphology of the samples was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and WS2 exfoliation was confirmed after liquid nitrogen and microwave treatments. Fourier transform infrared spectroscopy (FTIR) confirmed WS2 exfoliation during the exfoliation process. Optical bandgap calculation showed an increase in the exfoliation WS2 bandwidth to 4.7 eV, which is large enough for the massive indirect bandwidth (1.3 eV) of WS2, indicating the effect of quantum confinement. Decreased photoluminescence (PL) showed the production of defects in the samples during the processes. The tribological properties of WS2 nanoflakes as an additive in oil showed that the coefficient of friction and wear performance of the oil were significantly improved by adding WS2 nanoflakes synthesized by the hydrothermal method under different liquid nitrogen and microwave treatments. The results show that WS2 nanoflakes with an improved coefficient of friction and wear performance can be a promising additive that could open a new avenue for the large-scale production of tribological materials.