Influence of Ti/Al substitution on the structural features, magneitc properties and THz characteristics of M-type hexaferrites

Barium hexaferrite, Al substituted BaFe12-xAlxO19, Ti substituted BaFe12-xTixO19, and Al and Ti bisubstituted BaFe12-2xAlxTixO19 (with x = 0.0, 0.1, 0.5, and 1.0) were synthesized using a solid-phase method. The dopant content in the ceramics was controlled by its charge content. The effect of Al3+ or/and Ti4+ substitution on the crystal structure and properties of BaFe12-xAlxO19, BaFe12-xTixO19, and BaFe12-2xAlxTixO19 were studied. The phase purity and crystal structure of the ferrite solid solutions were studied by powder X-ray diffraction. Our investigation of the crystal structure confirmed the formation of a hexagonal single phase with space group P63/mmc (194) in the synthesized samples. In all Al-substituted samples, smaller Al ionic radii decreased cell parameters. In the other samples, aliovalent Ti4+ substitution might be due to the formation of Fe2+, decreased parameter a, and increased parameters c and V. The magnetization of all the samples was saturated at room temperature in fields of ∼3 T. The magnetization decreases for all samples. The coercivity decreased for BaFe12-xAlxO19 and for BaFe12-2xAlxTiхO19, it decreased likely due to changing the crystalline particle sizes. An increasing amount of dopants resulted in a monotonous reduction of the Curie temperature (TC). It was established for the first time that bisubstitution change the magnetic properties to values more significantly than the changes resulting from single cation substitution. By measuring room-temperature THz-IR spectra of real and imaginary permittivity, the doping effect on IR phonons and THz absorption was studied and compared with similar experiments performed for crystalline samples. The initial matrix cation substitution leads to the broadening of infrared phonon resonances. The effect is assigned to the charge-compensatory mechanisms in the compounds. Below a frequency of ≈5 cm−1, we discovered clear signatures of relaxation-type absorption, whose origin could be related to the disordered character of the ceramic samples. As result, it can be concluded that the structure and properties of initial matrix with a magnetoplumbite structure can be controllably optimized for electronics devices applications by Al3+ or/and Ti4+ substitution.