Spontaneous Vortex Nanodomain Arrays at Ferroelectric Heterointerfaces

The polarization of the ferroelectric BiFeO3 subjected to the different electrical boundary conditions by heterointerfaces is imaged with atomic resolution using a sphencal aberration correct transmission electron microscope. Unusual; triangular-shaped nanodomains are seen, and their role in providing polarization closure is understood through phase-field simulations. Heterointerfaces are key to the performance of ferroelectric devices, and this first observation of spontaneous vortex nanodomain arrays at ferroelectric heterointerfaces reveals properties unlike the surrounding film including mixed Ising-Neel domain walls, which will affect switching behavior, and a drastic increase of in polarization. The importance of magnetization closure has long been appreciated in multidomain ferromagnetic systems; imaging this analogous effect with atomic resolution at ferroelectric heterointerfaces provides the ability to see device-relevant interface issues. Extension of this technique to visualize domain dynamics is envisioned.