Enhanced magnetic anisotropy in lanthanum M-type hexaferrites by quantum-confined charge transfer

Iron-based hexaferrites are critical-element-free permanent magnet components of magnetic devices. Of particular interest is electron-doped M-type hexaferrite i.e., ${\mathrm{LaFe}}_{12}{\mathrm{O}}_{19}$ (LaM) in which extra electrons introduced by lanthanum substitution barium/strontium play a key role uplifting the magnetocrystalline anisotropy. We investigate electronic structure using density functional theory with localized charge density, reproduces semiconducting behavior and identifies origin very large Localized transfer from to iron at crystal's $2a$ site produces narrow $3{d}_{{z}^{2}}$ valence band strongly locking magnetization along $c$ axis. The calculated uniaxial anisotropy energies fully self-consistent calculations nearly double single-shot values, agree well available experiments. chemical similarity other rare earths suggests that LaM can host possessing nontrivial $4f$ states for, e.g., microwave-optical quantum transduction.