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Q & A: making magnets permanent

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Most recent answer: 10/22/2007
Q:
How do bar magnets become permantently magnatized? I know about the domains lining up but I want to know how they keep it from coming unalined if someone drops it or something.
- Rebecca Sztuczko (age 12)
Birch Run, Michigan, United States
A:
How to make good ’permanent’ magnets is a bit of an art. Even in materials that form strongly magnetized domains, there’s a tendency to lower the magnetic energy by having the domains line up to cancel the net magnetization. The best permanent magnets have various impurities and defects which tend to trap the ’walls’ between domains, keeping the most prevalent domain type from shrinking. Furthermore they have crystals which are much more easily magnetized along certain special directions, so the magnetization has a hard time smoothly turning to point some other way. The phrase used to describe that is ’magnetic anisotropy’. Still, too much heat or mechanical shock can partially demagnetize them,

Mike W.
Lee H

(published on 10/22/2007)

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