$M$-type hexaferrite is an optically active transition-metal oxide, characterized by a tunable band gap within the semiconducting range, along with inherent perpendicular magnetic and optical anisotropy. However, the nature of the optical band gap and associated transitions remains unclear due to its complex crystal structure. Here, we investigate the optical properties and electronic structure of ${\mathrm{SrFe}}_{12}{\mathrm{O}}_{19}$ (SrM) $M$-type hexaferrite using a combination of UV-visible diffuse reflectance spectroscopy, x-ray absorption spectroscopy (XAS), and first-principles calculations. The optical band gap, determined from derivative absorption spectra fitting, is consistent with generalized gradient approximation plus $U_{\text{eff}}$ calculations $(U_{\text{eff}}=3.7\mathrm{eV})$, whereas HSE06 overestimates the gap. Maximally localized Wannier functions constructed from O $2p$ and Fe $3d$ orbitals reveal site-dependent crystal-field splitting and mixed $t_{2g}\text{−}{e}_g$ hybridization. The electronic structure near the Fermi level $\left(E_F\right)$ is dominated by hybridized O $2p$ and Fe $3d$ states, which govern the optical transitions. Simulated O $K$- and Fe $L_{2,3}$-edge spectra reproduce experimental XAS, with O $K$ preedge features confirming covalency of O $2p/\mathrm{Fe}$ $3d$ hybridization. X-ray magnetic circular dichroism measurements further demonstrate the magnetic polarization of O $2p$ states induced by $\text{Fe-3}d$ hybridization, with site-specific contributions from inequivalent Fe sites. These results demonstrate that the optical transitions and electronic structure of SrM are primarily governed by O $2p/\mathrm{Fe}$ $3d$ hybridization and site-resolved crystal-field effects.

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• Crystal-field excitations
• Electronic structure
• Transition metal oxides
• Density functional calculations
• Optical absorption spectroscopy
• Wannier function methods