The effect of the citric acid to metal nitrates molar ratio on the structural and magnetic properties of strontium hexaferrite nanoparticles synthesized by the sol-gel combustion method

Strontium hexaferrite is a hard ferrite with the chemical formula of SrFe12O19 and has a magnetoplumbite structure. Due to high anisotropy, high saturation magnetization, chemical stability, high corrosion resistance, and appropriate Curie temperature, it has been widely used as a permanent magnetic material. A novel sol-gel combustion process was used to synthesize ultrafine particles of strontium hexaferrite. The weight ratio of citric acid to the total weight of strontium and iron salts nitrate (CA/MN) is among the parameters affecting the purity of SrFe12O19 nanoparticles produced by the sol-gel method, which can improve the purity of the final product by controlling this parameter. M-type SrFe12O19 nanostructures with different citric acid to metal nitrates molar ratios (0.5, 1, 2, and 4) were prepared. The results showed that nitrate-citrate gels exhibit self-ignition behavior after combustion in the air at room temperature. The samples were then characterized by XRD, TGA/DTA, FTIR, FE-SEM, VSM. The results showed that the crystallite size of strontium hexaferrite is significantly affected by the molar ratio of citric acid to metal nitrates. As the molar ratio of citric acid to metal nitrates increases, the size of nanostructures decreases. By increasing the molar ratio of citric acid from 0.5 to 1, the saturation magnetization and magnetic remanence magnetization increase, but the coercive field decreases.