Structural, microstructure and magnetic properties of superparamagnetic Mn sub(x)Mg sub(1-X)Fe sub(2)O sub(4) powders synthesized by sol-gel auto-combustion method

Ultrafine manganese magnesium ferrites Mn sub(x)Mg sub(1-x) Fe sub(2)O sub(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 super(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 sub(x)Mg sub(1-x)Fe sub(2)O sub(4) phase was formed at annealing temperature 1,200 degree C 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 super(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 super(2+) ion concentration up to 0.8. Furthermore, the change of carboxylic acid influenced the microstructure of the formed Mn sub(x) Mg sub(1-x)Fe sub(2)O sub(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 super(2+) ion molar ratio, and type of carboxylic acid. Good saturation magnetization (Ms = ~47.0 emu/g) was achieved with Mn super(2+) ion ratio 0.8 at annealing temperature 1,200 degree C 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 super(2+) ion content 0.5.