M-Type Strontium Hexaferrite Nanoparticles Prepared by Sol-Gel Auto-combustion Method: The Role of Co Substitution in Structural, Morphological, and Magnetic Properties

In this work, the sol-gel auto-combustion method has been successfully used to prepare nanocrystalline strontium hexaferrite doped with cobalt at iron sites (SrFe12-x Co-x O (19), x = 0-1). The crystal structure, morphology, and magnetic properties of samples were systematically investigated using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM), respectively. The three vibrational modes were observed in the FT-IR spectra of calcined samples, which indicated the presence of metal-oxygen stretching bands in hexaferrite structure after calcination treatment. The XRD results confirmed the single-phase M-type hexagonal structure for SrFe12-x Co-x O (19) samples with xae 0.5; however, for the samples with x > 0.5, the cubic CoFe2 O (4) phase was also appeared. The average particle size determined by TEM analysis was found to be about 87 nm (for x = 0) and 110 nm (for x = 1) whereas the cobalt substitution leads to the larger particles. The saturation magnetization increased with cobalt content up to x = 0.5 and then decreased slowly on further increase of the dopant concentration, while the coercivity decreased continuously with increasing Co content.