KAIST researchers, in collaboration with several institutions, experimentally confirmed the three-dimensional vortex-shaped polarization distribution inside ferroelectric nanoparticles. Using atomic electron tomography, they mapped the atomic positions in the barium titanate nanoparticles and calculated the internal polarization distribution. This discovery confirms theoretical predictions made 20 years ago and offers potential for the development of ultra-high density memory devices.
A
” data-gt-translate-attributes=”({“attribute”:”data-cmtooltip”, “format”:”html”})” tabindex=”0″ role=”link”>KAISTThe team-led research team successfully demonstrated the internal three-dimensional polarization distribution in ferroelectric nanoparticles, paving the way for advanced memory devices capable of storing more than 10,000 times more data than current technologies.
Materials that remain independently magnetized, without requiring an external magnetic field, are called ferromagnets. Likewise, ferroelectrics can maintain a polarized state themselves, without any external electric field, thus serving as an electrical equivalent to ferromagnets.
It is well known that ferromagnets lose their magnetic properties when reduced to nanoscale sizes below a certain threshold. What happens when ferroelectrics are also extremely small in all directions (i.e., in a zero-dimensional structure such as nanoparticles) has been a matter of controversy for a long time.
The research team led by Dr. Yongsoo Yang from the Department of Physics at KAIST has, for the first time, experimentally clarified the three-dimensional vortex-shaped polarization distribution inside ferroelectric nanoparticles through international collaborative research with POSTECH , SNU, KBSI, LBNL. , and the University of Arkansas.
About 20 years ago, Professor Laurent Bellaiche (currently at the University of Arkansas) and his colleagues theoretically predicted that a unique form of polarization distribution, arranged in the shape of a toroidal vortex, could occur at the inside ferroelectric nanodots. They also suggested that if this vortex distribution could be properly controlled, it could be applied to ultra-high density memory devices with capacities more than 10,000 times greater than existing ones. However, experimental clarification has not been achieved due to the difficulty of measuring the three-dimensional polarization distribution within ferroelectric nanostructures.
Advanced techniques in electron tomography
The KAIST research team managed to solve this 20-year-old challenge by implementing a technique called atomic electron tomography. This technique works by acquiring atomic-resolution transmission electron microscope images of nanomaterials at multiple tilt angles and then reconstructing them into three-dimensional structures using advanced reconstruction algorithms. Electron tomography can be considered essentially the same method as CT scans used in hospitals to view internal organs in three dimensions; the KAIST team adapted it only to nanomaterials, using a single-level electron microscope.
” data-gt-translate-attributes=”({“attribute”:”data-cmtooltip”, “format”:”html”})” tabindex=”0″ role=”link”>atom level.
Three-dimensional polarization distribution of BaTiO3 nanoparticles revealed by atomic electron tomography. (Left) Schematic of the electron tomography technique, which involves acquiring transmission electron microscope images at multiple tilt angles and reconstructing them into 3D atomic structures. (Center) Experimental determination of the three-dimensional polarization distribution inside a BaTiO3 nanoparticle via atomic electron tomography. A vortex-like structure is clearly visible near the bottom (blue dot). (Right) A two-dimensional cross-section of the polarization distribution, thinly sliced through the center of the vortex, with the color and arrows together indicating the polarization direction. A distinct vortex structure can be observed.
Using atomic electron tomography, the team completely measured the positions of cation atoms inside nanoparticles of barium titanate (BaTiO3), a well-known ferroelectric material, in three dimensions. From the precisely determined 3D atomic arrangements, they were able to further calculate the internal three-dimensional polarization distribution at the single-atom level. Polarization distribution analysis revealed, for the first time experimentally, that topological polarization orders including vortices, anti-vortices, skyrmions and a Bloch point occur inside 0-dimensional ferroelectrics , as theoretically predicted 20 years ago. Furthermore, it was also found that the number of internal vortices can be controlled based on their size.
Professors Sergey Prosandeev and Bellaiche (who with other colleagues proposed the theoretical order of polar vortices 20 years ago) joined this collaboration and further proved that the vortex distribution results obtained from the experiments are consistent with theoretical calculations.
By controlling the number and orientation of these polarization distributions, it is expected that this could be used in next-generation high-density memory devices, capable of storing more than 10,000 times the amount of information in a device of the same size compared to existing devices.
Dr. Yang, who led the research, explained the significance of the results: “This result suggests that controlling the size and shape of ferroelectric elements alone, without the need to adjust the substrate or surrounding environmental effects such as epitaxial deformation, can manipulate ferroelectric vortices or other topological orders at the nanoscale. Further research could then be applied to the development of next-generation ultra-high density memory.
Reference: “Revealing the three-dimensional arrangement of polar topology in nanoparticles” by Chaehwa Jeong, Juhyeok Lee, Hyesung Jo, Jaewhan Oh, Hionsuck Baik, Kyoung-June Go, Junwoo Son, Si-Young Choi, Sergey Prosandeev, Laurent Bellaiche and Yongsoo Yang, May 8, 2024,
Source link