Broadband electrodynamics of single-crystalline lead-substituted barium hexaferrite

Broadband electrodynamic response of single-crystalline lead-substituted barium hexaferrite Ba
1-x
Pb
x
Fe
12
O
19
is studied at temperatures from 5 to 300 K in the range of frequencies from 1 Hz to 240 THz. Discovered phenomena include relaxational radio-frequency dynamics of domains and domain walls, temperature-unstable terahertz excitations connected with electric dipoles induced by off-center displacements in the ab-plane of the lead ions, narrow terahertz excitations associated with electronic transitions between the fine-structure components of the Fe
²⁺
ground state, dielectric gigahertz resonances presumably of magneto-electric origin and polar lattice phonons.