Hydrothermal synthesis and competitive growth of flake-like M-type strontium hexaferrite

In this paper, single flake-like strontium hexaferrite was directly synthesized via a modified hydrothermal approach without high-temperature annealing. To determine the main factors governing the formation of the hexaferrite phase and impurity α-Fe₂O₃, effects of alkali environment and concentrations of metal ions on phase composition, grain growth, and magnetic properties were systematically analyzed. Results from XRD, FESEM and FT-IR analyses indicated that initial alkali concentration was the key factor influencing the phase composition of particles. Suitable initial alkali environment can enhance the nucleation and growth of ferrite, and inhibit the formation of by-product α-Fe₂O₃ at the same time. It was also found that the increase in initial concentration of strontium ions could improve the nucleation of hexaferrite and reduce the grain size, and consequently, change the magnetic performance of hexagonal particles. When the molar ratios of ferric ions to strontium ions were constant, the average grain size did not change significantly with the initial concentration of iron ions, which could be attributed to high levels of strontium ions and hydroxyl ions in the reaction system. The above-mentioned results indicate that the optimized hydrothermal conditions are beneficial for the formation of a single phase and for controlling the particle size and magnetic properties of M-type hexaferrite.