Enhancing magnetocrystalline anisotropy in W-type SrFe₁₈O₂₇ hexaferrite via tailored substitutions

W-type SrFe18O27 exhibits promising potential as a rare-earth-free “gap” permanent magnet due to its substantial magnetization and high Curie temperature. However, the commercial use of W-type SrFe18O27 hexaferrite is hindered by its limited coercivity, emphasizing the pivotal role of magnetocrystalline anisotropy energy (MAE). Addressing this challenge is crucial for advancing next-generation permanent magnets. Here, by performing comprehensive first-principles calculations, we investigate the intrinsic magnetic properties of pure W-type SrFe18O27 hexaferrite and its compositions with Sr0.5A0.5Fe18O27 (A = K, Ca, Ba, and La), aiming to enhance its MAE. The computed magnetic properties of the pure compound align well with prior experimental measurements showing a low uniaxial MAE of 0.148 MJ/m3. While the substitutions lead to increased MAE, the magnetic moments of different Fe sublattices and net magnetization (μ0Ms) exhibit minimal changes. Remarkably, La substitution yields a notably high uniaxial MAE of 0.582 MJ/m3, attributed to weakly localized charge transfer from La to the Fe(6g) site. The underlying mechanism for this enhancement involves the interplay of spin-orbit coupled dz2−dyz and dx2−y2−dxy states within the Fe(6g) and Fe(4f2) sublattices. La substitution proves particularly helpful in improving the anisotropy field (μ0Ha) and magnetic hardness parameter (κ). These findings underscore the potential of tailored substitutions to enhance MAE, providing exciting prospects for the practical development of W-type SrFe18O27 magnets, potentially rivaling the industrial standard M-type hexaferrite magnets.