Improved magnetic properties of self-composite SrFe12O19 powder prepared by Fe3O4 nanoparticles

Sintered polycrystalline strontium hexaferrite, which is one of the most widely used permanent magnetic materials, has been applied in many areas such as electrical and mechanical transductor devices. Improving the coercivity (HcJ) of M-type strontium hexaferrite with a nominal composition SrFe12O19 (SrM) plays an essential role to adapt to many modern applications, but is limited by the process and purity of raw materials. In this work, we prepared SrM powders with different iron resources, sintering temperatures, and Fe/Sr atom ratios. It was found that using Fe3O4 nanoparticles with a Fe/Sr atom ratio of 12 at 1100 °C performed the self-composites with 70% nano-size and 30% micro-size, which had the best performance. The coercivity reaches 348.9 kA/m, which is improved compared to pure SrM obtained by other iron resources in the solid-state method. This process shows a unique formation mechanism and the resulting self-composite microstructure eventually causes enhancement in the properties, which provides a new way for high-performance hexaferrites.