Structural, microstructure and magnetic properties of superparamagnetic Mn_xMg_(1-x)Fe_2O_4 powders synthesized by sol-gel auto-combustion method

摘要

Ultrafine manganese magnesium ferrites Mn_xMg_(1-x)Fe_2O_4 powders (x = 0.2, 0.4, 0.5, 0.6, 0.8) have been synthesized using a sol-gel auto-combustion method using tartaric acid as a fuel for the first time. The effect of synthesis conditions such as annealing temperature, Mn~(2+) ion molar ratio and type of carboxylic acid on the crystal structure, microstructure and magnetic properties was investigated using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer, respectively. The results demonstrated that well crystalline single cubic spinel Mn_xMg_(1-x)Fe_2O_4 phase was formed at annealing temperature 1,200 ℃ for time 2 h. The crystallite size, lattice parameter (a) and the unit cell volume were observed to increase as the annealing temperature and the Mn~(2+) content were increased. The microstructure of the formed powders was synthesis conditions dependent. The produced powders were found to be well defined cubic-like structure with high homogeneity by increasing Mn~(2+) ion concentration up to 0.8. Furthermore, the change of carboxylic acid influenced the microstructure of the formed Mn_xMg_(1-x)Fe_2O_4 powders as the results of change of the amount of released carbon dioxide and water vapor during the annealing. The magnetic properties were sensitive to annealing temperature, Mn~(2+) ion molar ratio, and type of carboxylic acid. Good saturation magnetization (Ms = ～ 47.0 emu/g) was achieved with Mn~(2+) ion ratio 0.8 at annealing temperature 1,200 ℃ for 2 h using tartaric acid as an organic fuel whereas the maximum saturation magnetization (Ms = ～ 49.4 emu/g) was obtained using citric acid as a fuel at the similar conditions and Mn~(2+) ion content 0.5.