Facile sonochemical preparation and magnetic properties of strontium hexaferrite (SrFe₁₂O₁₉) nanoparticles

The hard magnetic material M-type strontium hexaferrite (SrFe₁₂O₁₉) was prepared by a facile surfactantfree sonochemical strategy and subsequently by a calcination process. The surface morphologies, structures, and Curie temperature of the obtained final product was investigated by powder X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), BET (Brunauer– Emmett–Teller) specific surface area (SSA) and thermogravimetric analysis (TGA). XRD confirmed the formation of single-phase strontium hexaferrite with space group P63/ mmc (194) and hexagonal structure and the mean primary crystallite size was found to be 44 nm. The morphology of synthesized SrFe₁₂O₁₉ product was in spherical shape with good crystalline nature. The measured Curie temperature (T_c) of the nanoparticles was around 462 °C. The magnetic property of the sample was measured by using a Superconducting Quantum Interference Device (SQUID) magnetometer at temperatures between 4 and 300 K. The measured saturation magnetization (M_s) at 300 K, 33 emu/ g, is significantly lower than that found for bulk SrFe₁₂O₁₉, probably reflecting a size effect of the nano-particles.