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

W-type SrFe 18 O 27 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 SrFe 18 O 27 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 SrFe 18 O 27 hexaferrite and its compositions with Sr 0.5 A 0.5 Fe 18 O 27 ( 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/m 3 . While the substitutions lead to increased MAE, the magnetic moments of different Fe sublattices and net magnetization ( μ 0 M s ) exhibit minimal changes. Remarkably, La substitution yields a notably high uniaxial MAE of 0.582 MJ/m 3 , attributed to weakly localized charge transfer from La to the Fe(6 g ) site. The underlying mechanism for this enhancement involves the interplay of spin-orbit coupled d z 2 − d y z and d x 2 − y 2 − d xy states within the Fe(6 g ) and Fe(4 f 2 ) sublattices. La substitution proves particularly helpful in improving the anisotropy field ( μ 0 H a ) 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 SrFe 18 O 27 magnets, potentially rivaling the industrial standard M-type hexaferrite magnets.