Photo ccourtesy of Emily Ryan and Megan Holtz

Electron micrograph of the first room temperature multiferroic

November 8, 2016

Researchers Create First Room Temperature Stable Multiferroic

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Have you ever desperately needed to check Facebook or text a friend at the end of the day, only to find your phone out of battery? Or ended up staring at a blank, black laptop screen in the middle of that all important presentation? Well, for all of you, recent research published in Nature by Prof. Darrell Schlom, materials science, could soon make this frustration a thing of the past.

Schlom and team have synthesized a magnetoelectric multiferroic material that works at room temperatures. Such materials allow one to control magnetic fields by manipulating electric fields. Thus far, scientists have only created multiferroics that work at cryogenic temperatures (extremely low temperatures). Attempts at creating materials that work at higher temperatures, like bismuth iron oxide, have been futile because of their weak performance and challenges in putting them to practical use.

What makes these materials important is their ability to improve energy efficiency. A 2013 report by the Digital Power Group asserts that information and communication technology ecosystems worldwide use as much energy as Japan and Germany combined. Wide adoption of these magnetoelectric materials would allow devices to use considerably less energy and thus, reduce this footprint.

“This was a four-year odyssey in understanding what’s going on, and there were some perplexing results early on,” Schlom said.

Schlom and his team synthesized their multiferroic material from a ferromagnet and ferroelectric materials (materials that can be magnetically and electrically polarised externally respectively). Ferromagnetic materials have areas of uniform magnetization, known as magnetic domains, that can be shifted using magnetic fields.

The team used a ferromagnet, consisting of an atomic layer of lutetium oxide, followed by two layers of iron oxide. Ferroelectric materials are similar except, its electric domains can be moved using electric fields. Instead of two layers of iron oxide, the ferroelectric contained a single such layer.

“Consequently, the multiferroic material has domains that can be moved in several ways. In our case, we are interested in being able to move magnetic domains using electric fields,” Schlom said.

Under powerful electron microscopes, Schlom’s team noticed a wrinkle-like puckering of the lutetium oxide atomic layers.

According to Schlom, his collaborators first noticed this wrinkling while looking at the atomic structure of these films under powerful electron microscopes. This puckering was associated with higher temperature magnetism when these puckered layers were next to the double iron oxide atomic layers. Collaboration between researchers at many labs at both Cornell and elsewhere paved the way to understanding what was happening.

Schlom and his team deduced that the puckering allowed the internal magnetization to be in a single direction, thus, making it a powerful magnet, even at high temperatures. Consequently, combining these layers with ferroelectric materials would allow allow for this magnetization to be controlled by electric fields.

The team used a process known as Molecular Beam Epitaxy, or as Schlom refers to it, “atomic spray painting” to intersperse the ferroelectric material with an extra atomic layer of iron oxide.

They synthesized 15 such materials, adding the extra iron oxide layer at various positions in each structure. The first had an extra iron oxide layer after each ferroelectric layer whereas the fifteenth had one after every 15 layers.

After numerous tests, the team found that the ninth material performed best at high temperatures. However, the reason for this remains a mystery, especially because even powerful supercomputers cannot yet calculate the properties of a system with extra atomic layers spaced so far apart.

Schlom hopes future research will focus on answering this question and applying new knowledge to create materials that work at 100 degrees Celsius or higher. Such is its promise that Intel has begun funding the next phase of the lab’s research.