Why Al in Alnico
Most recent answer: 10/22/2007
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 its 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 thats 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 its no accident that a non-magnetic material helps break up the magnetism into those little pieces.
(published on 10/22/2007)