Cu2+ and Al3+ co-substituted cobalt ferrite: structural analysis, morphology and magnetic properties

Cu-Al substituted Co ferrite nanopowders, Co1-xCux Fe2-x Alx O4 (0.0 ≤ x ≤ 0.8) were synthesized by the co-precipitation method. The effect of Cu-Al substitution on the structural and magnetic properties have been investigated. X-ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM) are used for studying the effect of variation in the Cu-Al substitution and its impact on particle size, magnetic properties such as Ms and Hc. Cu-Al substitution occurs and produce a secondary phase, α-Fe2O3. The crystallite size of the powder calcined at 800°C was in the range of 19-26 nm. The lattice parameter decreases with increasing Cu-Al content. The nanostructural features were examined by FESEM images. Infrared absorption (IR) spectra shows two vibrational bands; at around 600 (v1) and 400 cm-1 (v2). They are attributed to the tetrahedral and octahedral group complexes of the spinel lattice, respectively. It was found that the physical and magnetic properties have changed with Cu-Al contents. The saturation magnetization decreases with the increase in Cu-Al substitution. The reduction of coercive force, saturation magnetization and magnetic moments are may be due to dilution of the magnetic interaction

Effect of size and indium-composition on linear and nonlinear optical absorption of InGaN/GaN lens-shaped quantum dot

Based on the Schrödinger equation for envelope function in the effective mass approximation, linear and nonlinear optical absorption coefficients in a multi-subband lens quantum dot are investigated. The effects of quantum dot size on the interband and intraband transitions energy are also analyzed. The finite element method is used to calculate the eigenvalues and eigenfunctions. Strain and In-mole-fraction effects are also studied, and the results reveal that with the decrease of the In-mole fraction, the amplitudes of linear and nonlinear absorption coefficients increase. The present computed results show that the absorption coefficients of transitions between the first excited states are stronger than those of the ground states. In addition, it has been found that the quantum dot size affects the amplitudes and peak positions of linear and nonlinear absorption coefficients while the incident optical intensity strongly affects the nonlinear absorption coefficients

Effect of Isothermal Conditions on the Charge Trapping/Detrapping Parameters in e-Beam Irradiated Thermally Aged XLPE Insulation in SEM

The effect of isothermal conditions on the trapping/detrapping process of charges in e-beam irradiated thermally aged XLPE insulation in scanning electron microscopy (SEM) has been investigated. Different isothermal conditions ranging from room temperature to 120 °C are applied on both unaged and aged XLPE samples (2 mm thick) by a suitable arrangement associated with SEM. For each applied test temperature, leakage, and influence currents have been measured simultaneously during and after e-beam irradiation. Experimental results show a big difference between the fresh and aged material regarding trapping and detrapping behavior. It has been pointed out that in the unaged material deep traps govern the process, whereas the shallow traps take part in the aged one. Almost all obtained results reveal that the trapped charge decreases and then increases as the temperature increases for the unaged sample. A deflection temperature corresponding to a minimum is observed at 50 °C. However, for the aged material, the maximum trapped charge decreases continuously with increasing temperature, and the material seems to trap fewer charges under e-beam irradiation at high temperature. Furthermore, thermal aging leads to the occurrence of detrapping process at high temperatures even under e-beam irradiation, which explains the decrease with time evolution of trapped charge during this period. The recorded leakage current increases with increasing temperature for both cases with pronounced values for aged material. The effect of temperature and thermal aging on electrostatic influence factor (K) and total secondary electron emission yield (σ) were also studied