Influence of chemical substitution on broadband dielectric response of barium-lead M-type hexaferrite

Abstract

We report on the electrodynamic properties of the single crystalline lead-substituted M-type barium hexaferrite, Ba 0.3 Pb 0.7 Fe 12 O 19 , performed in the broad frequency range including radio-frequency, terahertz and sub-terahertz bands, which are particularly important for the development of microelectronic devices. We demonstrate how changing on a molecular level the chemical characteristics (composition, intermolecular interaction, spin-orbital interaction) of lead-substituted M-type hexaferrite influences its radio-frequency and terahertz electrodynamic response. Our results indicate a critical temperature range, 50 K<T<70 K, where significant changes of the electrodynamic response occur that are interpreted as freezing of dynamical oscillations of bi-pyramidal Fe(2b) ions. In the range 5-300 K, the heat capacity shows no sign of any phase transition and is solely determined by electron and phonon contributions. An anomalous electrodynamic response is detected at 1-2 THz that features a rich set of absorption resonances which are associated with electronic transitions within the fine-structured Fe 2+ ground state and are visualized in the spectra due to magnetostriction and electron-phonon interaction. We show that lead substitution of barium in barium hexaferrite, BaFe 12 O 19 , leads to the emergence of a pronounced dielectric and magnetic relaxational dynamics at radio-frequencies and that both dynamics have the same characteristic relaxation times, thus evidencing the bi-relaxor-like nature of Ba 0.3 Pb 0.7 Fe 12 O 19 . We associate the origin of the relaxations as connected with the motion of magnetic domain walls. In order to unveil crucial influence of chemical substitution on electrodynamic characteristics of the compound, we analyze our results on substituted compound in comparison with the data available for pristine barium (BaFe 12 O 19 ) and pristine lead (PbFe 12 O 19 ) hexaferrites. The obtained spectroscopic data on the dielectric properties of Ba 0.3 Pb 0.7 Fe 12 O 19 provide insight into fundamental phenomena responsible for the absorption mechanisms of the compound and demonstrates that chemical ionic substitution is an effective tool to tune the dielectric properties of the whole family of hexaferrites.

Lead-substituted barium hexaferrite for tunable terahertz optoelectronics

“…For an extended picture of the IR phonon resonances for both compounds under study, see Supplemental Information, section SI2. The spectral response of the lattice vibrations observed in our compound is in line with the results obtained in other isostructural phases, such as the pure BaM 21 and Pb-substituted Ba 0.3 Pb 0.7 Fe 12 O 19 23 . The resonances in the spectra were modeled by Lorentzian expressions for the complex permittivity * ( )…”

“…SI5-3), we were not able to detect any sign of the domain polarity, that is most probably beyond the sensitivity of the used technique. This last suggestion is confirmed by the low values of dielectric strengths of the two relaxations, III and IV, Δε<≈10, which is by orders of magnitude less than those seen in pure BaM (Δε≈1000) 23 . We also note a considerable difference in activation energies of these relaxations, 18 meV (III) and 43 meV (IV).…”

“…3f) are also of limited precision because of the superimposed contribution of process IV which was not considered in the fits. Whereas relaxations I and II are extrinsic, the intrinsic relaxations III and IV might manifests the dynamical response of dielectric or magnetic domains, similar to a related compound with higher concentration of Pb, Ba 0.3 Pb 0.7 Fe 12 O 19 23 . In that compound, pronounced dielectric and magnetic relaxational dynamics were detected in the radio frequency range; both relaxations exhibit similar characteristic relaxation times, evidencing SI6-1) should be associated with magnetic domains dynamics.…”

Sub-lattice of Jahn-Teller centers in hexaferrite crystal

“…Magnetic oxides, containing iron ("ferrites"), crystallize in different structures. These materials are widely utilized or are promising candidates to be incorporated in various electronic devices owing to their magnetic, insulating, magnetoelectric and multiferroic properties [45][46][47][48][49][50][51] . An example of single crystal grown for our study is shown in Fig.…”

“…x 0 62, 0 75, 1 15 (this work and 61 ). The terahertz spectra of Ti-or Pb-substituted compounds were found to be determined mainly by electronic transitions of the tetrahedrally coordinated Fe 2+ ions (for details see 51 ). According to the charge compensation mechanism, in Ti 4+ -substituted BaFe 12-x Ti x O 19 hexaferrites with < .…”