Tuning the terahertz electrodynamics in Ba-Pb hexaferrite single crystals

L. Alyabyeva, E. Zhukova, S. Zhukov, A. Ahmed, D. Vinnik, B. Gorshunov

Abstract

First detailed measurements of broad-band (2–8000 cm⁻¹, i.e. 0.06-240 THz) temperature-dependent (5–300 K) spectra of complex permittivity of single-crystalline barium-lead hexaferrites Ba_1-xPb_xFe₁₂O₁₉ covering full interval of lead concentrations, x(Pb)=0…1, were performed to study the effect of Ba for Pb substitution on electrodynamic response. It is found that variation of Ba-Pb relative content allows “tuning” of dielectric losses ε“(0.3 THz; 300 K) from 0.1 to 45, and dielectric constant ε‘(0.3 THz; 300 K) from 10 to 50. To account for the discovered concentration evolution of terahertz dielectric properties, a microscopic model is suggested that considers interaction of 6s² lone pair of Pb²⁺ with nearest FeO₅ clusters. Pronounced anomaly in concentration-dependent oscillator strength of terahertz bands is observed at x(Pb)=0.5–0.6 and interpreted by considering redistribution of Fe²⁺/Fe³⁺ ions over five iron sublattices. It is pointed out that the revealed “tunability” of terahertz characteristics of hexaferrites makes them promising materials for designing devices operating at terahertz frequencies.

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