Large terahertz faraday rotation in high entropy M-type hexaferrites

Magneto-optical materials exhibiting strong Faraday rotation are essential for advanced non-reciprocal photonic and electronic devices. Beyond conventional doping, high-entropy design offers a novel paradigm for engineering functional properties by introducing atomic-scale configurational disorder. Here, high-entropy M-type hexaferrite (Ca_0.2Sr_0.2Ba_0.2Pb_0.2La_0.2)Fe₁₂O₁₉ (HEM) ceramics were prepared and characterized systematically. While retaining the hexagonal structure (P6₃/mmc), HEM displays significantly enhanced room-temperature magnetic properties (M_s ≈ 53.5 emu/g) and a giant Faraday rotation angle (~105°/mm) at 0.2 THz. Raman spectroscopy reveals that the elemental high entropy at the Me-site modifies the local Fe-O bonding, especially strengthening the Fe-O stretching at the 2b site, which may contribute to the enhanced Fe³⁺-O^2--Fe³⁺ superexchange interactions. Meanwhile, the refined domain structures may be associated with a higher domain wall density and are consistent with the enhanced magnetization under an applied magnetic field. These two contributions synergistically support the simultaneous enhancement of magnetic and magneto-optical responses. This work establishes high-entropy design as a powerful strategy for tailoring the magnetic properties and Faraday effect of M-type hexaferrites, paving the way for further innovations in advanced ferromagnetic materials.