Exploring the magnetic properties of W-type SrFe18O27 hexaferrite: Insights from a first-principles study

W-type SrFe18O27 hexaferrite is emerging as a potential material for permanent magnet applications. Despite this, theoretical modeling on W-type hexaferrites is still lacking, leaving only experimental findings to date. Employing density functional theory, we conduct a detailed analysis of pure W-type SrFe18O27 hexaferrite and its compositions with Ni/Zn substitutions, to explore their intrinsic magnetic properties and assess their viability as potential permanent magnets. We found no significant effect of Ni/Zn substitution on the magnetocrystalline anisotropy energy (MAE); however, Zn substitution is particularly helpful for improving the magnetization μ0Ms. The calculated MAE constant Ku values indicate that the compounds are uniaxial with easy axis along the (001) direction. The origin of the predicted MAE is investigated using second-order perturbation theory analysis and the electronic structure. We found that different Fe sublattices contribute differently to the MAE, providing a unique way to enhance the MAE with small site-specific substitutions. The results highlight the challenge of simultaneously enhancing Ku and μ0Ms in W-type hexaferrite compounds. However, the compounds show intriguing properties with moderate Ku and high μ0Ms, which may outperform the conventional M-type ferrite magnets in some applications.