A series of Al substituted yttrium iron garnet (Al-YIG) nanopowders with nominal formula of Y 3 Fe 5−x Al x O 12 which x varied in steps of 0.0, 0.5, 1.0, 1.5 and 2.0 were prepared via mechanochemical processing. The samples were milled for 40 h in a high energy planetary mill and then calcined at different temperatures from 1,300 to 1,100 • C. X-ray diffraction patterns reveal that the structure of nanopowders are bcc and the garnet phase has been obtained after calcining. The average crystallite sizes are in the range of 24-45 nm, using Scherrer's formula. The lattice constant of the samples decreases by increasing Al concentration. To investigate the site preference of Al 3+ ions, room temperature 57 Fe Mössbauer spectra for the samples were recorded and analyzed. The hyperfine field values for octahedral and tetrahedral sites of the samples decrease by increasing x value. This decrease in magnetic hyperfine field reflects a reduction of the superexchange interaction by the progressive substitution of Al for Fe, which is also evident in the behavior of the magnetization and T C for the samples.
Lead sulfide (PbS) thin films were prepared onto ultra-clean quartz substrate by the electron beam gun (EBG) evaporation method. The thicknesses of the thin films were 50, 100, 150and 200 nm. Theywere annealed at 423 K for 2 h. Field emission scanning electron microscopy (FESEM) images of the thin films showed their texture morphologyat the surface of the quartz substrate. X-ray diffraction (XRD) patterns of the thin films showed that theyhave a cubic phase and rock-salt structureafter annealing. The average crystallite size for the thin films was in the range of 32-100 nm. Optical measurements confirmed that crystalline thin films have a direct band gap that increases by decreasing the film thickness. This blue shift of the band gap of thin films compared to the bulk structure can be attributed to the quantum confinement effects in the nanoparticles. A decrease in conductivity by increasing the temperature confirmed the positive temperature coefficient of resistance in the thin films that showed the dominant conduction mechanism is via a band-like transition. The density of localized states at the Fermi level increases by increasing the film thickness. Current-voltage behavior of the thin films showed an increase in both dark current and photocurrent by increasing the crystallite size which is discussed, based on the presence of trap states and barriers in nanostructures.
The purpose of this research is to find out a perpendicular nanomagnetic cell with optimum dimensions by using Object Oriented Micromagnetic Framework (OOMMF) simulation. The optimum perpendicular nanomagnetic cell is characterised and the effect of nano-size on the performance of the cell is explored. Nanomagnetic basic gates are implemented by applying the proper arrangement of nanomagnetic cells. The optimum size of nano cell is 50 × 30 × 5 nm. In this survey, all designs are implemented by employing 3-input and 5-input minority gates. The clock signal, which is a uniform magnetic external field, is needed for proper performance of gates. An irreversible 2-input XOR gate is suggested by these gates based on perpendicular nanomagnetic cells. Moreover, the power dissipation is a major concern in digital circuits. It was proved that the heat dissipation will be very low in reversible circuits. Therefore, the reversible XOR gates are suggested by applying the proposed gates in this study. The correctness of operation of the presented gates is verified by using MagCAD tool. According to the simulation results, the proposed 2-input XOR gates in a single layer have significant improvement in terms of gate count, delay and complexity in comparison to the previous design.
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