kjmagnetics

Hang on a second. I have to go check and see who won the betting pool for how long it would take this meme to surface. ;) Unavoidable with this job title...

I'll play the role of a literal-minded engineer and answer it: Richard Feynman's explanation is still my favorite. YouTube link. How much of an answer is enough to satisfy you? You can sense is irritation and impatience with the question.

This video explanation from the Veritasium guy is also pretty good. Ultimately, though, it comes to the same conclusion as Feynman: it just does. That's the way the universe seems to work.

It's all about coercivity. That's the fancy word for how much a magnet resists getting demagnetized in a magnetic field.

Like when you magnetize a steel screwdriver by wiping a magnet along it, but it doesn't seem to last. That's because the steel has very low coercivity. The magnetic field it has tends to actually demagnetize itself.

Early magnets had lower coercivity. The horseshoe shape (and the use of a steel keeper) were fancy ways of adjusting the magnetic circuit to keep the thing from demagnetizing itself.

Alnico magnets, like those found in home alarm systems and electric guitars, are better, but still not as high coercivity as neodymium magnets. You find Alnico in horseshoes or long cylinders to prevent demagnetization.

Neodymum magnets aren't just stick-to-the-fridge strong, they're also harder to demagnetize. Like, you need an MRI machine magnetic field to do it. It also means you can have a thin disc magnet, which wouldn't stay magnetized with old magnet material.

This article has some better explanation with pictures: Why are magnets shaped like horseshoes?

Ironically, that horseshoe shape of our mascot isn't really needed for neodymium magnets.

The strongest permanent magnet material is a neodymium magnet. We haven't discovered or made anything stronger.

Now, when you start getting electricity involved, people have made much stronger magnets. Think scientific research, particle colliders, etc.

I think the 45 Tesla (!) magnet down at the National High Magnetic Field Lab in Florida is as big as they come. For reference, keep in mind that a 16 T field is strong enough to levitate water, like the levitate a frog experiment.

Yes, I've heard that a lot. I've demagnetized a slightly magnetized piece of steel this way. I've even affected an Alnico magnet with a hammer.

I've tried to characterize how impacts demagnetize neodymium magnets and failed pretty miserably. It seems that the strength of the impact that you need to see any meaningful demagnetization is strong enough to break the magnet.

"Look, I've demagnetized the magnet"

"Dude, it's in 18 pieces on the ground. No kidding it's demagnetized."

Nah, I don't think so. Now more people are thinking about magnets! ;)