Sonochemical assisted synthesis of SrFe₁₂O₁₉ nanoparticles

We present the synthesis of M-type strontium hexaferrite by sonochemistry and annealing. The effects of the sonication time and thermal energy on the crystal structure and magnetic properties of the obtained powders are presented. Strontium hexagonal ferrite (SrFe₁₂O₁₉) was successfully prepared by the ultrasonic cavitation (sonochemistry) of a complexed polyol solution of metallic acetates and diethylene glycol. The obtained materials were subsequently annealed at temperatures from 300 to 900 °C. X-ray diffraction analysis shows that the sonochemical process yields an amorphous phase containing Fe³⁺, Fe²⁺ and Sr²⁺ ions. This amorphous phase transforms into an intermediate phase of maghemite (γ-Fe₂O₃) at 300 °C. At 500 °C, the intermediate species is converted to hematite (α-Fe₂O₃) by a topotactic transition. The final product of strontium hexaferrite (SrFe₁₂O₁₉) is generated at 800 °C. The obtained strontium hexaferrite shows a magnetization of 62.3 emu/g, which is consistent with pure hexaferrite obtained by other methods, and a coercivity of 6.25 kOe, which is higher than expected for this hexaferrite. The powder morphology is composed of aggregates of rounded particles with an average particle size of 60 nm.