Magnetized Materials

You can easily magnetize a nonmagnetized ferromagnetic material by placing it in a magnetic field. For example, if you put a nonmagnetized iron nail near a magnet, you will turn the nail into a magnet. Figure 5B shows the alignment of magnetic domains in magnetized iron. The applied magnetic field causes magnetic domains aligned with the field to grow larger. This magnetization can be temporary. If the magnet is moved away from the nail, the motion of the atoms in the nail causes the magnetic domains to become randomly oriented again. In some ferromagnetic materials, the domains stay aligned for a long time. These materials are called permanent magnets. They are not truly permanant, because heat or a jarring impact can realign the domains.

If you cut a magnet in half, each half will have its own north pole and south pole because the domains will still be aligned. If you cut the pieces in half again, each half will again have a north pole and a south pole. No matter how many times you cut the magnets, each piece will have two different poles. A magnet can never have just a north pole or just a south pole.

Figure 5 A magnetic field can magnetize ferromagnetic materials.

A Before magnetization, domains are random. B Domains aligned with the field grow during magnetization. Unaligned domains can shrink.