RESUMO
Nano-sized pure and Cd-doped ZnFe2O4 (Zn(1-x)Cd(x)Fe2O4 with x = 0.0-0.5) samples were synthesized by a simple microwave combustion method. The X-ray diffraction (XRD) analysis confirmed the single phase cubic spinel structure. The average crystallite size was found in the range of 17.47-41.21 nm. The lattice parameter is found to increase with increase in the concentration of Cd. Pure ZnFe2O4 and all compositions of the Zn-Cd ferrites showed similar particle-like morphologies, which is confirmed by high resolution scanning electron microscopy (HR-SEM). Energy dispersive X-ray (EDX) analysis shows that the theoretical and observed percentage of the elements; Zn2+, Cd2+ and Fe3+ are in the desired stoichiometric proportion. The UV-Visible diffuse reflectance spectrum (DRS) shows the band gap value increases with increasing Cd content. All the samples showed the characteristic near-band-edge emission at around 428 nm, which is observed by photoluminescence (PL) spectra. The magnetic properties were measured by using vibrating sample magnetometer (VSM) and it was found that the saturation magnetization is increased with increase the concentration of Cd content. The results revealed that for lower Cd concentration (x = 0.0-0.2) the samples shows a superparamagnetic behavior, whereas for higher concentration (x = 0.3-0.5), it becomes ferromagnetic.
RESUMO
Cobalt oxide (Co3O4) nanoparticles were synthesized by microwave combustion method (MCM) using urea as the fuel. For the purpose of comparison, they are also prepared by conventional combustion method (CCM). The prepared samples were examined by using X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), high resolution transmission electron microscopy (HR-TEM), UV-Visible diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy and vibrating sample magnetometer (VSM). XRD analysis indicated that the as-prepared samples have well-crystalline cubic phase. HR-TEM images showed that Co3O4 nanoparticles have sphere-like structure with an average particle size in the range of 20-25 nm (MCM) and 45-50 nm (CCM). Optical properties of Co3O4 nanoparticles revealed the presence of two band gap (1.89 and 2.54 eV (MCM), 1.68 and 2.38 eV (CCM)) values, which in turn confirmed the semi-conducting properties. VSM measurements revealed a small hysteresis loop at room temperature thus indicating a weak ferromagnetism.
