Title. How is it different from the types of magnetism we already knew about?
In: Physics
First, the kinds of magnetism we already knew about:
**Ferromagnetism**
This is your typical fridge magnet. You’ve probably heard this explanation before but if not, here’s how they work. A magnetic field is really an electric field but moving (kind of). Each electron is *kind of sort of not really but kind of* spinning in place like a top. Since electrons have an electric charge – an electric *field* – their “movement” as they spin generates a magnetic field. Around atoms, electron form shells that contain two electrons: one with spin up, and one with spin down. Because of the opposite spin, the magnetic fields are opposite. If the shell is full, the magnetic fields cancel each other out and there’s no net magnetic field.
If the shell is *not* full, then that atom has a very very tiny net magnetic field coming from that atom. If a lot of atoms happen to align such that all of those tiny magnetic fields are pointed the same way, you get a *region* that has a bigger magnetic field. However, for most materials, these regions are all mixed up and pointed in every direction so they cancel each other out and, again, there’s no net magnetic field. If enough *regions* are aligned, then you have a permanent magnet.
**Antiferromagnetism**
This is the opposite of ferromagnets. They do not show any net magnetism. In these materials, the electrons and crystals and regions are all arranged so that they are opposite of each other, canceling each other out so that there is no larger magnetic field. Anything that *doesn’t* stick to the fridge is showing antiferromagnetism. This property took longer to figure out, even though it’s kind of the “default” property, because first scientists had to figure out why ferromagnets existed.
**Altermagnetism**
Altermagnets (as far as I can tell from some quick research) are kind of like halfway between ferromagnets and antiferromagnets. That is, the electrons alternate in their spin direction (like antiferromagnets) so that the overall magnetic field cancels out and it won’t stick to your fridge. However, the electrons are aligned in crystal lattices that are big enough to create bands of opposing magnetic fields.
If we zoom *waaaaay* in, imagine each atom is like its own tiny magnet. Put them together in the same direction and you get a bigger magnet. Put the bigger magnets together and you get a fridge magnet, aka a ferromagnet. If you put the tiny magnets together in opposite directions, and you get not a magnet, aka an antiferromagnet. If you put the tiny magnets together to make bigger magnets, and then put *some* of the bigger magnets together, and *some* of them in opposite directions, you get an altermagnet. In other words, an antiferromagnet has regions pointed in every direction, which completely cancels out the magnetic fields. Altermagnets have regions that are opposite, so they cancel out, but they’re larger like in a ferromagnet and they are more directly opposing each other instead of being all over the place.
They’re called altermagnets because if you were an electron whizzing along next to one, your spin would be forced to *alternate* as you passed through the bands of the opposing magnetic fields.
**Usefulness**
Electronics take advantage of electric fields – that’s the flow of electricity that we use to make circuits and flow through logic gates that make computers. *Spintronics* try to use the spin of individual electrons. This is the “quantum computing” that everyone loves to talk about. Since spintronics are manipulating the spin of electrons to store and transmit data, you need to be able to, you know, *do that* – you need to be able to change the spin, which is what ferromagnets do. On the other hand, the spin of a single electron is *extremely* sensitive to magnetic fields – duh, because that’s what was just used to change it on purpose. So, you also want to build your machine using antiferromagnets so there’s no big magnetic field around to change the spin when you don’t want it to change. And, you need to move the electron around through your machine without its path being disrupted by a magnetic field. If only there was a type of magnet that had magnetic fields big enough to manipulate individual electrons’ spin, but still had zero net magnetic field so it wouldn’t be disruptive when it shouldn’t be…oh hey, look, altermagnets! Maybe!
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