Transport, magnetic, and structural properties of La${}_{0.7}$Ce${}_{0.3}$MnO${}_3$ thin films. Evidence for hole-doping

Abstract

Cerium-doped manganite thin films were grown epitaxially by pulsed laser deposition at $720^{\circ }$C and oxygen pressure $p_{O_2}=1-25$Pa and were subjected to different annealing steps. According to x-ray diffraction (XRD) data, the formation of CeO${}_2$ as a secondary phase could be avoided for $p_{O_2}\ge 8$Pa. However, transmission electron microscopy shows the presence of CeO${}_2$ nanoclusters, even in those films which appear to be single phase in XRD. With O${}_2$ annealing, the metal-to-insulator transition temperature increases, while the saturation magnetization decreases and stays well below the theoretical value for electron-doped La${}_{0.7}$Ce${}_{0.3}$MnO${}_3$ with mixed Mn${}^{3+}$/Mn${}^{2+}$ valences. The same trend is observed with decreasing film thickness from 100 to 20 nm, indicating a higher oxygen content for thinner films. Hall measurements on a film which shows a metal-to-insulator transition clearly reveal holes as dominating charge carriers. Combining data from x-ray photoemission spectroscopy, for determination of the oxygen content, and x-ray absorption spectroscopy (XAS), for determination of the hole concentration and cation valences, we find that with increasing oxygen content the hole concentration increases and Mn valences are shifted from 2+ to 4+. The dominating Mn valences in the films are Mn${}^{3+}$ and Mn${}^{4+}$, and only a small amount of Mn${}^{2+}$ ions can be observed by XAS. Mn${}^{2+}$ and Ce${}^{4+}$ XAS signals obtained in surface-sensitive total electron yield mode are strongly reduced in the bulk-sensitive fluorescence mode, which indicates hole-doping in the bulk for those films which do show a metal-to-insulator transition.

arXiv comment8 pages, 10 figures

References in corpus (5)

• Double Exchange Alone Does Not Explain the Resistivity of $L{a}_{1-x}S{r}_{x}Mn{O}_3$
• Direct observation of electron doping in La0.7Ce0.3MnO3 using x-ray absorption spectroscopy
• A 'p-n' diode with hole and electron-doped lanthanum manganite
• Temperature-Dependent X-Ray Absorption Spectroscopy of Colossal Magnetoresistive Perovskites
• Electronic structure and transport properties of La_0.7Ce_0.3MnO_3

Cited by in corpus (7)

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• Hall effect in heavy-fermion metals
• Properties of the electron-doped infinite-layer superconductor Sr${}_{1-x}$La${}_x$CuO${}_2$ epitaxially grown by pulsed laser deposition
• 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
• Epitaxial stabilization of ultra thin films of electron doped manganites
• Mn${}^{2+}$/Mn${}^{3+}$ state of La${}_{0.7}$Ce${}_{0.3}$MnO${}_3$ by oxygen reduction and photodoping
• Conductivity and magnetoresistance of La${}_{0.7}$Ce${}_{0.3}$MnO${}_3$ thin films under photoexcitation