Mesoscale flux-closure domain formation in single-crystal BaTiO3

Over 60 years ago, Charles Kittel predicted that quadrant domains should spontaneously form in small ferromagnetic platelets. He expected that the direction of magnetization within each quadrant should lie parallel to the platelet surface, minimizing demagnetizing fields,and that magnetic moments should be configured into an overall closed loop, or flux-closure arrangement. Although now a ubiquitous observation in ferromagnets, obvious flux-closure patterns have been somewhat elusive in ferroelectric materials. This is despite the analogous behaviour between these two ferroic subgroups and the recent prediction of dipole closure states by atomistic simulations research. Here we show Piezoresponse Force Microscopy images of mesoscopic dipole closure patterns in free-standing, single-crystal lamellae of BaTiO3. Formation of these patterns is a dynamical process resulting from system relaxation after the BaTiO3 has been poled with a uniform electric field. The flux-closure states are composed of shape conserving 90° stripe domains which minimize disclination stresses

Enhanced electric conductivity at ferroelectric vortex cores in BiFeO3

In many large ensembles, the property of the system as a whole cannot be understood from studying the individual entities alone ¿ these ensembles can be made up by neurons in the brain, transport users in traffic networks or data packages in the Internet. The past decade has seen important progress in our fundamental understanding of what such seemingly disparate 'complex systems' have in common; some of these advances are surveyed here

Flexible polarization rotation at the ferroelectric/metal interface as a seed for domain nucleation

The absence of a realistic polarization screening scenario at the pivotal ferroelectric-metal interface impedes the widespread application of low-dimensional ferroelectric heterostructures. Employing quantitative atom-resolved (scanning) transmission electron microscopy and first-principles calculations, we report that structural and chemical reconstruction universally lowers symmetry of the ferroelectric-metal interface. Irrespective of structural and strain mismatch, chemical termination and diffusion, polar catastrophe, and electrode type, the polarization screening is executed by a flexible polarization rotation at several-unit-cell-thick interfaces. By combining nanoscale and atomic-scale microscopy investigations, our ex situ electric-field biasing experiments reveal that the monoclinically distorted interfaces may act as seeds to nucleate new domains during the polarization switching process. These findings suggest that the long-standing fatigue issue is expected to be overcome by interface modification engineering at the monolayer scale