Preparation and magnetic properties of Sm and Co/Zn/Ca co-doped SrFe12O19 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.