A new class of materials that eventually could be incredibly useful in designing new methods of computer memory has been discovered by a team of international scientists. The discovery is published in the Sept. 18 issue of Nature Communications.
Headed by Christos Panagopoulos of Nanyang Technological University in Singapore, the researchers investigated heterostructures layered at the atomic level- different materials were deposited in layers a few atoms thick. They found that the new class of materials has a very desirable property: ferroelectricity.
The ferroelectricity was observed in synthetic tri-layer superlattices made up of non-ferroelectric NdMnO3/SrMnO3/LaMnO3 layers. Why is this property desirable? Ferroelectricity could be used to create new types of data storage devices.
Spontaneously Polarizating Heterostructures
A ferroelectric material shows unprompted electrical polarization, characterized by a positive electric charge on one side of the material and negative on the opposite side. The polarization can be reversed by applying an electric field, for instance from a battery. These two possible polarization orientations make these materials attractive for developing computer memory because each orientation could correspond to 0 or 1.
“Our discovery shows a possibility that researchers could engineer properties at the atomic scale and create new, artificial materials exhibiting novel functional properties not existing in their constituents,” said physicist Evgeny Tsymbal, Professor of Physics and director of University of Nebraska-Lincoln’s Materials Research Science and Engineering Center (MRSEC). “This significantly broadens the class of known ferroelectric materials and provides possibilities to design new ferroelectrics.”
The new materials were fabricated by researchers from Nanyang Technological University in Singapore, the Foundation for Research and Technology-Hellas in Greece, and Sungkyunkwan University in South Korea.
Using advanced synthesis methods, the team was able to fabricate heterostructures by depositing atomic layers of different materials, layer-by-layer, in stacks of thickness of a few nanometers. To put his in perspective, one nanometer is 1 billionth of a meter. Although neither of the component materials alone were ferroelectric, the composed heterostructures showed a pronounced ferroelectric polarization.
The reason for this was unclear at first, but the UNL scientists found the explanation for this phenomenon. They modeled the atomic structure and electronic properties of these materials by performing computations at UNL’s Holland Computing Center, which indicated that interfaces between the constituent materials in the heterostructures were responsible for the observed novel properties.
“Crucially, our computations and analysis were decisive for the understanding of the origin of ferroelectricity in the experimentally synthesized heterostructures,” Tsymbal said. “We were able to elucidate the microscopic mechanism responsible for their exciting properties.”
Also, said Tsymbal, the discovered materials exhibited magnetoelectricity, an important functional property that allows it to affect electric polarization by the application of a magnetic field. “This functionality is especially interesting because of potential application in electrically-controlled data storage with significantly reduced energy consumption,” Tsymbal said. “Our MRSEC dedicates strong efforts to study magnetoelectric materials and has international recognition in this field of research.”
Tunable ferroelectricity in artificial tri-layer superlattices comprised of non-ferroic components K. Rogdakis, J.W. Seo, Z. Viskadourakis, Y. Wang, L.F.N. Ah Qune, E. Choi, J.D. Burton, E.Y. Tsymbal, J. Lee & C. Panagopoulos Nature Communications 3, Article number:1064 doi:10.1038/ncomms2061
Image by Marilyn Roxie, Creative Commons Attribution