La³⁺-Induced Band-Gap Modifications in Barium Hexaferrite: An Investigation of the Structural, Optical, and Dielectric Properties †

M-type barium hexaferrites, BaFe_(12−x)La_xO₁₉ (x = 0.0, 0.05, 0.1, 0.15, and 0.2), were prepared by a low-cost solid-state reaction method. The specimens crystallized in a non-centrosymmetric hexagonal magnetoplumbite structure that belonged to the P6₃/mmc space group. Morphologically, the samples were dense with hexagonal plate-like grains and size variations of around 1.19–1.70 μm. The optical band gap of the system was reduced in the wide band-gap region from 1.78 to 1.74 eV. The band-gap values would be useful in photocatalysis and photovoltaics. The AC conductivity was enhanced with La³⁺ substitution, following Jonscher’s power law. Maxwell–Wagner-type polarization was observed in the specimen, and tangent loss decreased with La³⁺ substitution. The values of the tangent loss were in the appropriate range for electromagnetic shielding applications.