Magnets: How do they stop working?

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Magnetism is slightly weird. Iron becomes magnetic because lots of electrons agree to align their individual magnetic moments. If you hit a thin layer of iron with a strong, very short pulse of light, however, the strength of its magnetic field will drop almost immediately.

How does this happen? Well, until now, we weren't really sure. Thanks to the magic of X-ray lasers we now know why: sound waves carry angular momentum of electrons away.

Disappearing magnetism induces a headache

The problem with disappearing magnetism is related to something called the conservation of angular momentum. Think of the Earth, a gigantic spheroid spinning in space: its spin is angular momentum, which is always conserved. If the Earth loses angular momentum, something else must gain angular momentum to compensate.

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