You’ve probably heard of ferromagnetism, materials that become magnetic in a magnetic field, but have you heard of ferroelectricity? And what do hysterons have to do with it? Wait what are hysterons anyway? Ok, I’m getting ahead of myself, let’s go back to ferroelectricity. Ferroelectricity isn’t related to iron like you might think, but it gets its name because it’s analogous to ferromagnetism. Ferromagnetic materials like iron are made up of magnetic domains that have north and south poles.

If these domains line up, the material itself becomes magnetic. Likewise, ferroelectric materials are made of crystals that are electric dipoles, meaning they have a separated positive and negative charge. If these dipoles line up, the material itself will have a positive and negative pole. Usually, the dipoles are pointing in random directions, but they can be coerced into uniformity. The same way iron’s domains can line up when exposed to a strong enough external magnetic field, a ferroelectric’s dipoles will line up when exposed to a strong enough electric field.





They’ll stay that way when the field is removed, as though they have a memory, and because of that memory when another electric field is applied that can change the dipole’s directions they’ll lag behind orienting to the new field, a phenomenon called hysteresis. In a ferroelectric material, the switch doesn’t happen all together like it ideally should, different parts of it change direction at different times.





Figuring out exactly why took more than 80 years of searching. In 1935 a german specialist scientifically portrayed ferroic materials as little free parts called hysterons. Each hysteron would change it’s polarization at a well-defined speed when exposed to a strong enough field, but each hysteron could also have a different critical field than its neighbors. Meaning a magnetic or electric field that was strong enough to change one hysteron would have no effect on the hysteron next to it.





The model works and accurately describes the behavior of ferroelectrics, but nobody was sure what hysterons actually were and the physics of why they behaved that way. That was until 2018 when researchers studied two organic ferroelectric materials and observed stacks of disc-shaped molecules a few nanometers high. The stacks’ different sizes and tight packing meant they all strongly interacted with each other, causing them to react differently to the different field strengths.





Finally, we witnessed hysterons and confirmed why ferroelectrics line up their dipoles at the speed they do. That wasn’t the only breakthrough in our understanding of ferroelectrics in 2018. I know, you just learned about them and they’re already advancing at a breakneck pace. See, ferroelectrics can be permanently polarized, meaning their dipoles stay aligned even after the field is removed until another critical field aligns them in another direction. That property means they have potential use in computer storage. Many computers today still use a magnetic hard drive to store data, but creating a magnetic field requires a large current. Ferroelectrics could use less power to store data, but until recently they had a scaling problem.





The crystals could only get so small until the aligned dipoles became unstable. Roughly eight years ago though, researchers in Germany claimed they made a ferroelectric material that did the opposite: it kept its dipoles aligned when thinner than 10 nanometers, but when it got thicker it lost its ferroelectric properties. A group of skeptical scientists tried to simplify the material and recreate the results, and much to their surprise they did.

In fact, their results were even better than before. It turns out at that small scale, the crystals were under immense pressure that caused a different arrangement of their structures and a polar phase. As an added bonus the substrate used to grow the crystals was also magnetic, opening up the possibility of magnetic and ferroelectric storage on the same drive, allowing for more data can be stored in the same space.





Don’t expect ferroelectric computer storage to hit shelves tomorrow, there are a lot more hurdles the technology would have to clear. But If one day in the future, you’re shopping for a new computer and you start seeing the flashy marketing term “Ferroelectric hard drive,” just remember you heard it here first.



