Investigation of structural and magnetic properties of nanocrystalline Mn-doped SrFe12O19 prepared by proteic sol-gel process

Nanoparticles of SrFe12-xMnxO19 (x=0.0 and 0.10) were synthesized by a proteic sol-gel process. Thermogravimetric and differential thermal analyses (TG-DTA) indicated the formation of nanocrystalline strontium ferrite phase at a calcination temperature of 1000 °C. Structural and microstructural evolutions of the samples were studied by X-ray powder diffraction (XRD) and the Rietveld method. XRD patterns demonstrated that all samples consisted of single-phase M-type strontium hexaferrite. The crystal lattice constant did not change significantly with manganese substitution, ranging from 0.5877(3) nm (x=0.0) to 0.5876(3) nm (x=1.0). In addition, the average crystallite size, which was determined from the Williamson-Hall formula, was about 46.4-52.6 nm. Infrared spectroscopy (FT-IR) showed the presence of three principal absorption bands in the frequency ranges around 435-535 cm−1 and around 595 cm−1, indicating the formation of the hexaferrite. Scanning electron microscopy (SEM) revealed that particles consisted of irregular platelets with sizes from 68 to 204 nm. Room-temperature Mössbauer investigations revealed that manganese ions preferentially occupied the 12k, 4f1, 4f2, and 2a sites. Hysteresis loops (M-H) showed that the saturation magnetization, remanence, and coercivity decreased with manganese doping. This effect is discussed in terms of the distribution of metal cations in the tetrahedral and octahedral sites.