Preparation and magnetic properties of Sm and Co/Zn/Ca co‐doped SrFe ₁₂ O ₁₉ hexaferrite

High‐performance SrFe 12 O 19 meets the current demands for lightweight and high‐efficiency devices. In this study, Sm‒(Co/Zn/Ca) co‐doped spherical SrFe 12 O 19 powders were synthesized via ultrasonic spray pyrolysis. This approach overcomes the limitation of single Sm doping in M‐type strontium ferrite, which enhances coercivity but decreases saturation magnetization. The effects of co‐doping on the structural and magnetic properties of the material were systematically investigated using X‐ray diffraction, Raman spectroscopy, X‐ray photoelectron spectroscopy, scanning electron microscopy, Brunauer–Emmett–Teller, Mössbauer spectroscopy, and both room‐temperature and low‐temperature vibrating sample magnetometry (VSM). Among all the synthesized samples, SrSm 0.20 Zn 0.05 Fe 11.75 O 19 exhibited the highest saturation magnetization ( M s = 78.983 emu/g) while maintaining a coercivity of 7.097 kOe. Compared to SrSm 0.20 Fe 11.80 O 19 , Sm‒Zn co‐doping resulted in a 20.12% increase in M s with only a 0.42% reduction in H cj . The results indicate that Zn 2+ preferentially substitutes Fe 3+ at the 4f 2 spin‐down sites, reducing the contribution of reverse magnetic moments and thereby enhancing M s . Additionally, as a non‐magnetic ion, Zn 2+ does not disrupt Fe‒O‒Fe super‐exchange interactions, leading to a minimal reduction in H cj . In contrast, Ca 2+ tends to occupy the 12k and 2a spin‐up sites, which reduces spin‐up magnetic moments, negatively affecting M s enhancement. Moreover, Co 2+ , being a magnetic ion, disturbs Fe‒O‒Fe super‐exchange interactions when incorporated into the SrFe 12 O 19 lattice, leading to a more significant decrease in coercivity. The magneton number ( n B ) calculated from low‐temperature VSM confirmed the magnetic moment enhancement effect in the co‐doped system, while Mössbauer spectroscopy provided further insights into the hyperfine interactions. This study demonstrates that the Sm‒(Co/Zn/Ca) co‐doping strategy effectively balances M s and H cj , significantly improving the magnetic performance of SrFe 12 O 19 . Furthermore, ultrasonic spray pyrolysis proves to be a scalable and cost‐effective synthesis method, showing great potential for the large‐scale production of high‐performance ferrite powders. These findings provide a theoretical foundation for optimizing SrFe 12 O 19 magnetic properties and offer new perspectives for its application in permanent magnet technology.