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how can you destroy magnetism?
Actually, it's not hard to wreck a magnet. The little magnetic domains exert forces on each other that push them to change their alignment. Except in some very special cases (tiny iron whiskers, for example) those forces push the domains toward lining up so that they cancel each other's long-range magnetic field. In a good magnet, the domains stay stuck lined up together (so their fields add up together) for a long time, but if you accidentally heat one up, or even drop it, it will partially or completely demagnetize. It will stay demagnetized unless you anneal it in a strong applied field. That's why development of magnets is such an art.
(republished on 07/13/06)
Follow-Up #1: temperature and magnets
DO you mean that heat destroy magnet. Do you know any of it ? And air con and refrigerator are cold and I am wandering that are these not suitable to use for destroying or not.
Yes, we definitely mean that heating up a magnet enough will destroy its magnetism, for the reasons described above.
Cooling an ordinary magnet will not destroy its magnetism.
(published on 04/15/09)
Follow-up on this answer.