Vortex-Antivortex Network Formation in BiFeO₃/SrTiO₃/BiFeO₃ Multilayers

Ferroelectric vortices in low-dimensional ferroelectric oxides have attracted intense spotlight due to their applicational functionalities in nanoelectronics. For data storage devices, rhombohedral-phase BiFeO₃ is one of the most prominent candidates for its stable polar vortex configurations, switchable with controlled manipulations. However, the identification of these vortices is still challenging and needs to be explored widely in complex polar structures, especially in rhombohedral-phase systems exhibiting all possible eight variants of polarization. In case BiFeO₃ shows two out-of-plane polarization projections, identification of all vortices by their polarization projections at one specific plane (usually the (001) plane) may hide the actual identity for many of them. Here, comprehensive research has been demonstrated by designing a unique multilayer BiFeO₃/SrTiO₃/BiFeO₃ thin film over SrTiO₃ (001) substrate to create eight polarization variants at the top BiFeO₃ layer. X-ray diffraction, reciprocal space mapping, and scanning transmission electron microscopy data confirm high epitaxial growth, while piezoelectric force microscopy is performed at the top layer for the mapping of polar domain textures. Identification of these vortices has been performed by projecting the polarizations not only at the (001) plane but also at other planes to prove the precise identity of these vortices.