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Why are alnico magnets made with aluminum if AL is not magnetic? Is it just a filler material? If so, why put it in the name?
great question. It turns out that if you make a really pure crystal of
something that spontaneously magnetizes very well, like iron, nickel,
or cobalt, it makes a lousy permanent magnet. The reason is that it's
too easy for the magnetic domains to rotate their magnetization
directions. The lowest energy state is one where the total magnetism
from the different domains cancels, so that's what the thing turns into
on its own. Breaking the magnetism up into lots of little pieces each
stuck in a locally asymmetrical environment reduces the total magnetism
in the little regions but makes it much harder for the magnetization to
realign. That makes it possible to make 'permanent' magnets, which stay
aligned for a very long time. So it's no accident that a non-magnetic
material helps break up the magnetism into those little pieces.
(published on 10/22/2007)
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