The maximum strength of a magnet occurs when all of the magnetic
dipoles of the atoms point the same direction. Each atom is a little
magnet, and we get the best results if they are all lined up.
This rarely occurs in magnetic materials, such as iron, as they
are found in nature, in which only a percent (or so) of the atoms are
aligned. (Neighboring ones align well in little domains, but those
domains tend to point different ways.) Thus, the strength can be
increased if we can line up those domains more.
To twist the domains into alignment (sounds brutal, no?), we put
the magnetizable material in a big magnetic field. We can either put it
near another, *very* strong, magnet, or we can wrap a coil of wire
around it and run a lot of electric current through the wire (making an
electromagnet). It helps if the material is heated first, and then
cooled down when exposed to the big magnetic field.
How well this works depends on the kind of material the natural
magnet is made of. Some materials are easier to magnetize than others.
Jon (w Mike W)
(republished on 07/13/06)