Electrical-transport characteristics of as-grown and oxygen-reduced La${}_{0.7}$Ce${}_{0.3}$MnO${}_3$ films: calculation of hopping energies, Mn valences, and carrier localization lengths

Abstract

Presently, cerium-doped LaMnO${}_3$ is vividly discussed as an electron-doped counterpart prototype to the well-established hole-doped mixed-valence manganites. Here, La${}_{0.7}$Ce${}_{0.3}$MnO${}_3$ thin films of different thicknesses, degrees of CeO${}_2$ phase segregation, and oxygen deficiency, grown on SrTiO${}_3$ single crystal substrates, are compared with respect to their resistance-vs.-temperature (R vs. T) behavior from 300~K down to 90~K. While the variation of the film thickness (and thus the degree of epitaxial strain) in the range between 10~nm and 100~nm has only a weak impact on the electrical transport, the degree of oxygen deficiency as well as the existence of CeO${}_2$ clusters can completely change the type of hopping mechanism. This is shown by fitting the respective \textit{R-T} curves with three different transport models (adiabatic polaron hopping, Mott variable-range hopping, Efros-Shklovskii variable-range hopping), which are commonly used for the mixed-valence manganites. Several characteristic transport parameters, such as the hopping energies, the carrier localization lengths, as well as the Mn valences are derived from the fitting procedures.

arXiv comment9 pages, 3 figures

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