Local Electrical Conductivity of Multiferroic Domain Walls

There is an intense interest in magnetoelectric coupling between electric and magnetic due to its potential to the revolutionary of device architectures. Single-phase multiferroics - materials that show spontaneous magnetization and polarization simultaneously at ambient conditions – remain elusive as most systems (such as the manganites) exhibit multiferroicity only at low temperatures. Alternatively, multiferroics can be synthesized as a composite system, e.g. as a product property of a composite phase consisting of a magnetostrictive and a piezoelectric material. One multiferroic material, however, has played a key role in rejuvenating the field after a report of large ferroelectric polarization combined with interesting magnetic properties - BiFeO$_{3}$. Here we provide evidence of a unique property of single domain walls in multiferroic BiFeO$_{3}$. Unlike other multiferroic materials, e.g. PbTiO$_{3}$, on which the electronic properties of the domain walls are not significantly different from the domain area, we observe a finite electric conductivity at room temperature along such a wall using conductive atomic force microscopy. This intrinsic property of the domain wall is attributed to a changed crystallographic structure as revealed by high resolution transmission electron microscopy. Additionally, optical absorption measurements confirm a change in bandstructure at domain walls in BiFeO$_{3}$.