Effect of aluminium substitution on low energy electrodynamics of barium-lead M-type hexagonal ferrites

摘要

We present the first detailed study of the terahertz-infrared dielectric response of single crystalline lead-substituted M-type barium hexaferrites doped with Al~(3+). The broadband spectra of complex dielectric permittivity ε~*(v)=ε'(v)+iε"(v) of Ba_(0.8)Pb_(0.2)Al_xFe_(12-x)O_(19) with concentrations of the dopant x(Al)=1.2, 3, 3.3 are obtained for two principle polarizations using Fourier-transform infrared spectroscopy and terahertz time-domain spectroscopy in the temperature range from 4 to 300 K and at frequencies from 10 cm~(-1) up to 8000 cm~(-1). We observe a rich set of excitations and assign them to the electronic transitions within the ground state 5E of the 4-fold coordinated divalent iron and to phonon resonances. Effect of Al~(3+) cation substitution on low energy (terahertz) dielectric response and infrared phonon spectra of barium-lead M-type hexaferrites is analysed and discussed.