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Q & A: magnetic domains

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Most recent answer: 10/22/2007
Q:
could you please explain the domai theory in magnets? how is it different from the popular molecular theory?
- nimish (age 15)
India
A:
I have no idea what the ’popular molecular theory’ is, but can say a bit about domains.
Ferromagnetic domains form when there’s an interaction between the electrons in a material such that their energy can be lowered by aligning their magnetic moments. These relatively short-range interactions are a consequence of quantum mechanics. At some point as the material is cooled, this possibility of lowering energy by lining up the electronic magnets overcomes the random jostling from thermal energy, and an aligned state starts to form. If that’s all there was to it, the state formed would in principle involve the whole material lining up together. However, there is also a weak classical magnetic torque operating over long distances which favors different parts pointing opposite directions. Except for unusual sizes and shapes of samples, that torque is strong enough on long distance scales to make the magnetism break up into domains pointing different directions. On short scales, the domains are still well-aligned.

Mike W.

(published on 10/22/2007)

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