Conduction at Domain Walls in Oxide Multiferroics

Department of Physics, University of California, Berkeley, 94720 California, USA.
Nature Materials (Impact Factor: 36.5). 02/2009; 8(3):229-34. DOI: 10.1038/nmat2373
Source: PubMed


Domain walls may play an important role in future electronic devices, given their small size as well as the fact that their location can be controlled. Here, we report the observation of room-temperature electronic conductivity at ferroelectric domain walls in the insulating multiferroic BiFeO(3). The origin and nature of the observed conductivity are probed using a combination of conductive atomic force microscopy, high-resolution transmission electron microscopy and first-principles density functional computations. Our analyses indicate that the conductivity correlates with structurally driven changes in both the electrostatic potential and the local electronic structure, which shows a decrease in the bandgap at the domain wall. Additionally, we demonstrate the potential for device applications of such conducting nanoscale features.

    • "Recent developments for functional twin boundaries are summarized by Salje (2010, 2012) and Salje and Zhang (2009); the possibility of using mobile magnetic boundaries as functional elements in memory devices was first proposed in racetrack technology by Stuart Parkin (2008a,b). Other crucial developments are the discovery of highly conducting boundaries by Jan Seidel and collaborators (Seidel et al., 2009, 2010) and superconducting twin walls by Aird and Salje (1998, 2000). Ferroelectric twin walls in ferroelastic CaTiO 3 were predicted by Goncalves-Ferreira et al. (2008, 2010) and the chemical enrichment of the twin walls by Calleja et al. (2003). "
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    ABSTRACT: In ferroelastic materials, the existence of degenerate strain states leads to the formation of nanoscale microstructures, such as domain boundaries (twin walls) and tweed. As the symmetry properties of microstructures differ from those of the bulk, they may dramatically change the macroscopic properties of a crystal. In addition, they are likely to have functional properties (ferroelecricity, piezoelectricity, magnetism, conductivity and rapid chemical transport) that are absent in the bulk. The existence of functional properties of twin walls, along with the advances in nano-scale characterization, has opened the door to domain boundary engineering, which aims to use domain boundaries as active elements in device materials. Hence, this relatively new field puts ferroelastic twin walls and possibly tweed at the heart of future electronic devices. Ferroelasticity is very common among minerals. Similar to man-made materials, the same crystallographic principles apply, which means that there are many minerals that await discovery for their functional properties. Thus, this review aims to raise attention to the discovery of minerals with functional microstructures. The current development of functional twin boundaries and tweed structures in physics and materials sciences is compared with the traditional observation of such structures in minerals. With an emphasis on chemical transport and piezoelectric/ferroelectric behaviour, examples of functional microstructures are given from both man-made materials and minerals in addition to a discussion of the origin of polar twin walls and the introduction of a recent experimental technique, resonant piezoelectric spectroscopy (RPS), for their discovery.
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    • "Topological defects are widespread in condensed matter physics, and interactions among topological defects and the resulting configurations of numerous topological defects can be associated with various intriguing phenomena123 because they are insensitive to continuous deformation or perturbation. Topological defects in hexagonal RMnO3 (R = Ho to Lu, Y, and Sc), domain walls/vortices, are responsible for their multiferroicity which is characterized by the coexistence of multi-ferroic orders. "
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    ABSTRACT: Topological vortices with swirling ferroelectric, magnetic and structural anti-phase relationship in hexagonal RMnO3 (R = Ho to Lu, Y, and Sc) have attracted much attention because of their intriguing behaviors. Herein, we report the structure of multiferroic vortex domains in YMnO3 at atomic scale using state-of-the-art aberration-corrected scanning transmission electron microscopy (STEM). Two types of displacements were identified among six domain walls (DWs); six translation-ferroelectric domains denoted by α+, γ-, β+, α-, γ+ and β-, respectively, were recognized, demonstrating the interlocking nature of the anti-vortex domain. We found that the anti-vortex core is about four unit cells wide. In addition, we reconstructed the vortex model with three swirling pairs of DWs along the [001] direction. These results are very critical for the understanding of topological behaviors and unusual properties of the multiferroic vortex.
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