Polarons in Magnetoelectric Fluorides

Abstract

The complex dielectric constant/ac electrical conductivity was investigated as a function of the frequency and temperature in four fluorides systems, K₃Fe₅F₁₅, K₃Fe₂Cr₃F₁₅, (NH₄)₂FeF₆, and Pb₅Cr₃F₁₉. All studied fluorides systems undergo ferroelectric (or antiferroelectric) phase transition at higher temperatures, and ferromagnetic (or antiferromagnetic) transition at low temperatures. At lower temperatures, in all studied systems, the real part of the complex ac electric conductivity was found to follow the universal dielectric response σ′ ∝ ν ^s , being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that, at low temperatures, this mechanism governs the charge transport in all studied fluoride systems.

Keywords:

• Ferroelectrics
• ferromagnetic
• dielectric properties
• tunneling
• polarons

Acknowledgments

This work was supported by the Slovenian Research Agency under program P1-0125.