Impedance spectroscopy of epitaxial multiferroic thin films

Temperature dependent impedance spectroscopy enables the many contributions to the dielectric and resistive properties of condensed matter to be deconvoluted and characterized separately. We have achieved this for multiferroic epitaxial thin films of $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ (BFO) and $\mathrm{Bi}\mathrm{Mn}{\mathrm{O}}_{3}$ (BMO), key examples of materials with strong magnetoelectric coupling. We demonstrate that the true film capacitance of the epitaxial layers is similar to that of the electrode interface, making analysis of capacitance as a function of film thickness necessary to achieve deconvolution. We modeled non-Debye impedance response using Gaussian distributions of relaxation times and reveal that conventional resistivity measurements on multiferroic layers may be dominated by interface effects. Thermally activated charge transport models yielded activation energies of $0.60\ifmmode\pm\else\textpm\fi{}0.05\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ (BFO) and $0.25\ifmmode\pm\else\textpm\fi{}0.03\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ (BMO), which is consistent with conduction dominated by oxygen vacancies (BFO) and electron hopping (BMO). The intrinsic film dielectric constants were determined to be $320\ifmmode\pm\else\textpm\fi{}75$ (BFO) and $450\ifmmode\pm\else\textpm\fi{}100$ (BMO).