Abstract
In this Letter we highlight direct experimental evidence of - charge ordering at room temperature in hematite-ilmenite epitaxial thin films grown by pulsed laser deposition, using aberration-corrected scanning transmission electron microscopy coupled to high-resolution energy electron-loss spectroscopy. These advanced spectromicroscopy techniques demonstrate a strong modulation of the valence state along the axis. Density functional theory calculations provide crucial information on the key role of oxygen vacancies in the observed charge distributions. Their presence at significant levels leads to the localization of extra electrons onto reduced sites, while Ti remains solely . The magnetic and transport properties of these films are reviewed in the light of the present results regarding their ferrimagnetic character correlated with the modulation and their semiconducting behavior interpreted by an Efros-Shklovskii variable-range hopping conduction regime via and centers. The experimental evidence of only one type of mixed valence state, i.e., and , in the system will thus help to interpret further the origin of its geomagnetic properties and to illuminate fundamental issues regarding its spintronic potential.
- Received 30 March 2013
DOI:https://doi.org/10.1103/PhysRevLett.111.167202
© 2013 American Physical Society