Ferromagnetism: Feynman's Physics Explained
Ferromagnetism is the strong magnetism of iron. It springs from a purely quantum effect, the 'exchange interaction,' which makes the spins of electrons in neighboring atoms line up spontaneously even with no outside field. This creates large fully magnetized regions called domains. Magnetizing iron means growing the domains aligned with the field and rotating the others, and the resistance to that change produces hysteresis.
The big idea
Iron is strongly magnetic because electron spins line up in domains.
Think about it
Why does a paperclip become a temporary magnet near a strong magnet, then mostly lose it afterward?
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