I also like how they explained ferromagnetism as being arranged atomic magnets. Magnets all the way down.
> The common one, the fridge magnet, is ferromagnetic — its atomic magnets all point the same way (up or down), adding their magnetic effects.
Ferromagnets typically have domains with magnetic moments that point in different directions. Ferromagnets rarely have every 'atomic magnet' pointing the same way.
https://en.wikipedia.org/wiki/Magnetic_domain
Refrigerator magnets in particular are usually magnetized as Halbach arrays, where the whole point is that the 'atomic magnets' are not pointing in the same direction. This is more energetically stable, which allows you to use cheaper materials.
https://en.wikipedia.org/wiki/Refrigerator_magnet
Lastly, I believe most refrigerator magnets are actually ferrimagnetic, not ferromagnetic. (The distinction doesn't matter much for users of magnets, but is important for the materials scientists studying and designing them.)
Are there any other really unique characteristics of magnets that you find really interesting that most people would not know?
- Superconductors are perfect diamagnets and can levite on (or hang from) ferromagnets: https://www.youtube.com/watch?v=ZHT6NIebSfU)
- Superconductor quantum interference devices (SQUIDs) use the quantization of superconducting electron tunneling to measure tiny amounts of magnetic field, as little as a millionth of a flux quantum: https://en.wikipedia.org/wiki/SQUID
- Ferromagnetism is intrinsically a quantum phenomenon; spin is quantized and iron's magnetism is explained, in part, from electrons being identical particles that obey the exclusion principle: https://farside.ph.utexas.edu/teaching/sm1/Thermalhtml/node8...
- Despite the "super", superconductors are mostly not used in the world's strongest electromagnets, as they have limits on the current and magnetic fields they can take
- Magnetizing a magnet will actually cause it to spin a little, macroscopically: https://en.wikipedia.org/wiki/Einstein%E2%80%93de_Haas_effec...
- Charged particles are affected by magnetism even when traveling through space where electric and magnetic fields are zero: https://en.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect
- Magnetic spin systems can technically have negative temperature: https://en.wikipedia.org/wiki/Negative_temperature
- Everything is magnetic, even frogs: https://www.youtube.com/watch?v=KlJsVqc0ywM