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 researcher mathematically described ferroic materials as small independent
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 a 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 it’s 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’s 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.
Computer storage is one area where a lot of different fields of study have a lot of promise,
like the potential to store data on a single atom.
Check out my video on that here.
Those tiny lab grown crystals had pressures up to 5 gigapascals inside the crystal, or
over 49,000 times the atmospheric pressure at sea level.
Thanks for watching, don’t forget to subscribe, no pressure, and I’ll see you for more Seeker.