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

Nanoparticles of SrFe_12-xMn_xO₁₉ (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. - Highlights: • Samples have hexagonal phase with space group P6₃mmc. • The present samples sintered at 1000 °C for 1 h. • The M_s and the H_c decreased at low doping contente Mn x=0.10. • M-type SrFe₁₂O₁₉ have been synthesized via the proteic sol–gel process