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Local Structure of Amorphous EuO–TiO2 Thin Films Probed by X-Ray Absorption Fine Structure

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  • This research was partially supported by the MEXT Grant-in-Aid for Scientific Research (B) (No. 22360273), Challenging Exploratory Research (No. 21656163), and Priority Research (No. 22015011). One of the authors (H. A.) thanks the Grant-in-Aid (No. 22-1280) from JSPS.

Author to whom correspondence should be addressed. e-mail: fujita@dipole7.kuic.kyoto-u.ac.jp

Abstract

We have investigated the local structure of amorphous oxides in EuO–TiO2 system to understand the mechanism that gives rise to curious ferromagnetic properties recently observed in the system. X-ray absorption spectroscopy has been performed on amorphous EuTiO3 and Eu2TiO4 thin films prepared by the pulsed-laser-deposition method. The TiK-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data analyses reveal that the coordination number of Ti4+ in the amorphous thin films is around 4, which is in sharp contrast to their crystalline counterparts, where Ti4+ ions are octahedrally coordinated by oxide ions. It is therefore inferred that Ti4+ acts as a network-forming cation in the random network structure of the amorphous oxides. From the EuL3-edge EXAFS data analyses, it is found that the coordination number of Eu2+ is much lower and the nearest Eu–O bond length is shorter in the amorphous thin films than in the crystalline counterparts. The amorphization-induced enhancement of ferromagnetic interactions observed in the EuO–TiO2 system is discussed in terms of the local environment around Eu2+ ions.

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