MSE461_09_23_11_Choquette_Paper_ConductionatDomainWalls

MSE461_09_23_11_Choquette_Paper_ConductionatDomainWalls -...

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ARTICLES PUBLISHED ONLINE: 25 JANUARY 2009 DOI: 10.1038/NMAT2373 Conduction at domain walls in oxide multiferroics J. Seidel 1,2 * , L. W. Martin 2,3 * , Q. He 1 , Q. Zhan 2 , Y.-H. Chu 2,3,4 , A. Rother 5 , M. E. Hawkridge 2 , P. Maksymovych 6 , P. Yu 1 , M. Gajek 1 , N. Balke 1 , S. V. Kalinin 6 , S. Gemming 7 , F. Wang 1 , G. Catalan 8 , J. F. Scott 8 , N. A. Spaldin 9 , J. Orenstein 1,2 and R. Ramesh 1,2,3 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. C orrelated oxide systems are an exciting and challenging area of condensed-matter research, with their interacting and competing charge, spin, orbital and lattice degrees of freedom forming new electronic and magnetic phases 1,2 . These phases can be controlled through stress, optical excitation and electric and magnetic fields and have great potential for applications in the fields of spintronics, information storage and communications. Among the correlated oxides, the multiferroics, which show more than one type of ferroic order in the same phase, are attracting particular interest 3–6 . The defining characteristic of a ferroic material is an order parameter (electric polarization in ferroelectrics, magnetization in ferromagnets or spontaneous strain in ferroelastics) that has different, energetically equivalent orientations, the orientation of which can be selected using an applied field. This often leads to the appearance of domains of differently oriented regions, separated by domain walls, coexisting in a sample 7 . Such domain walls will become more technologically important as the dimensions of individual elements in devices continue to shrink. Although the morphology and properties of domains and their walls have been studied for more than 50 years, in recent times there has been increasing focus on novel functionality at domain walls 8–12 . For example, it has been predicted theoretically that the ferroelectric walls in magnetoelectric multiferroics can be ferromagnetic even if the domains themselves are antiferromagnetic 9–11 . Conversely, spin rotation across ferromagnetic domain walls in insulating ferromagnets can induce a local polarization in the walls of an otherwise non-polar material 5,12 . Experimentally, unusual functional properties of domain walls have also been observed:
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MSE461_09_23_11_Choquette_Paper_ConductionatDomainWalls -...

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