Terahertz spectroscopy of lead-substituted barium hexaferrites Ba1-xPbxFe12O19

Using methods of terahertz time-domain spectroscopy dielectric response of ceramic barium hexaferrites substituted with lead (Ba1_-xPbxFe₁₂O₁₉, x = 0.00-0.30) was studied in the frequency range of 3-110 cm¹ and at temperatures from 5 to 300 K. Obtained spectra are presented by a rich set of lines of different nature, i.e. excitations associated with electronic transitions within the fine-structure components of Fe²⁺ ions, A_2u soft optical phonon, and ferroelectric-like soft mode. The frequency of the soft mode reveals power-law temperature variation v_SM ∼ (T-T_c)⁰²⁵ , which indicates a potential phase transition atr_c. Analysis shows that T_c approaches zero for the concentrations x = 0.20-0.25.