Publication Type:Journal Article
Source:Nano Letters, American Chemical Society, Volume 18, Number 2, p.717-724 (2018)
Keywords:bismuth compounds, Bismuth ferrites, Differential phase contrast, Differential phase contrast imaging, Doping (additives), Ferroelectric polarization, ferroelectricity, Functional properties, High resolution transmission electron microscopy, iron compounds, Periodic distortions, Polarization, Polarization gradients, scanning electron microscopy, scanning transmission electron microscopy, Semiconductor doping, transmission electron microscopy
The ultimate challenge for the development of new multiferroics with enhanced properties lies in achieving nanoscale control of the coupling between different ordering parameters. In oxide-based multiferroics, substitutional cation dopants offer the unparalleled possibility to modify both the electric and magnetic properties at a local scale. Herein it is demonstrated the formation of a dopant-controlled polar pattern in BiFeO3 leading to the spontaneous instauration of periodic polarization waves. In particular, nonpolar Ca-doped rich regions act as spacers between consecutive dopant-depleted regions displaying coupled ferroelectric states. This alternation of layers with different ferroelectric state creates a novel vertical polar structure exhibiting giant polarization gradients as large as 70 μC cm-2 across 30 Å thick domains. The drastic change in the polar state of the film is visualized using high-resolution differential phase-contrast imaging able to map changes in ferroelectric polarization at atomic scale. Furthermore, a periodic distortion in the Fe - O - Fe bonding angle suggests a local variation in the magnetic ordering. The findings provide a new insight into the role of doping and reveal hitherto unexplored means to tailor the functional properties of multiferroics by doping engineering. © 2018 American Chemical Society.
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