Atomic Asymmetry and the Next Generation of Data Storage

One of physics’ greatest tricks is polarization. Take magnets, for example, such as those commonly found on refrigerators holding up shopping lists and Christmas cards. These have the familiar north/south polarization that we can experience as attraction and repulsion. That magnetic orientation persists all the way down to the individual molecules, which actually align to cause the larger-scale behavior.

This polar phenomenon is caused by ferromagnetism, a defining quality of some particles that gives them an intrinsic polarity – what scientists call a dipole moment. And remarkably, that magnetic moment can be manipulated. Applying an external magnetic field to ferromagnetic materials can flip the orientation, turning north into south, attraction into repulsion.

That ferromagnetic flip is happening rapidly inside computer hard drives right now. Magnetic polarization can translate directly into computer code: north and south become the binary building blocks that underlie nearly the entire digital world. Computers apply a field to toggle between the two states, signifying 1 or 0 – this is how data is written, read, and rewritten on hard disk drives. Ferromagnetics are ideal candidates for this because they’re non-volatile, meaning that they retain orientation even when a device powers down.

But magnets aren’t the only game in town. Electricity also enjoys polar play in the form of positive and negative charges, and they’ve got their own class of non-volatile materials: ferroelectrics. These materials also feature a dipole moment that can be flipped, but by an external electric field. This then easily corresponds to binary computer code. And when you take this down to the billionth of a meter scale, exciting things happen that could shake up the next generation of computers.

“Ferroelectric materials can retain information on a much smaller scale and with higher density than ferromagnetics,” said Brookhaven physicist Yimei Zhu, one of the authors on a breakthrough paper published in Nature Materials. “We’re looking at moving from micrometers (millionths of a meter) down to nanometers (billionths of a meter). And that’s what’s really exciting, because we now know that on the nanoscale each particle can become its own bit of information.”

Direct polarization images of individual ferroelectric nano cubes captured with electron holography. The fringing field, or “footprint” of electric polarization, can be seen clearly in (a), but it vanishes when the material is subjected to high temperatures (b). The lower images show that no fringing field can be observed before application of electricity (c), but a clear field emanates after current is applied (d).

Brookhaven Lab scientists  demonstrated a method to “see” into the atomic structure of ferroelectrics, revealing the source of their unique data-storage potential, and laying the foundation for future electronic data devices. The new study also tested nanoscale integrity and probed ferroelectric stability with a range of electric voltages and temperature conditions.

The electron holography techniques employed (see the Predator-vision image to the right) clearly captured the ferroelectric field and its remarkable origin: atomic displacement. Each ferroelectric particle features an internal asymmetry, or polar ordering, that gives rise to its electric polarization. When the charge flips, the structure of the particle itself changes. The study also revealed that ferroelectric particles require about five nanometers of critical elbow room when scaled up to prevent polarity interference that could corrupt data in electronics.

Read more about the research at Brookhaven’s press release, including more on ferroelectric footprints and the incredibly precise electron holography techniques employed by scientists.