Effect of annealing temperature on structural and magnetic properties of strontium hexaferrite nanoparticles synthesized by sol-gel auto-combustion method

In this paper, strontium hexaferrite nanoparticles were synthesized by the sol-gel auto-combustion method. Effect of annealing temperature on crystal structure, morphology and magnetic properties of nanoparticles was investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). Also, the thermal decomposition of as-synthesized powdered samples has been studied by thermogravimetric analysis (TGA). The XRD patterns confirmed the formation of single phase M-type hexagonal crystal structure for powders annealed above 950 degrees C, whereas the presence of hematite (alpha-Fe2O3) as secondary phase was also observed for sample annealed at 900 degrees C. Furthermore, the crystallinity along with the crystallite size were augmented with annealing temperature. Comparison of the FT-IR spectra of the samples before and after annealing treatment showed the existence of metal-oxygen stretching modes after annealing. The thermogravimetric analysis confirmed the thermal decomposition of as-burnt powders happened in three-stage degradation process. The TEM images showed the nanoparticles like hexagonal-shaped platelets as the size of nanoparticles increases by increasing the annealing temperature. With increasing annealing temperature, the magnetic saturation and the coercivity were increased to the maximum value of 74.26 emu/g and 5.67 kOe for sample annealed at 1000 degrees C and then decreased.