Magnets are made of ferromagnetic materials that have been magnetized. Ferromagnetic materials include nickel, iron, rare earth elements and naturally occurring minerals such as lodestone.
Magnets are created by magnetizing certain materials by exposing them to an external magnetic field. These materials are known as ferromagnetic or ferrimagnetic materials. Most non-ferromagnetic materials will react to a magnetic field to some extent; but in contrast to ferromagnetic materials, they will only do so weakly and will not remain magnetized when the external field is removed. Such materials are known as paramagnetic.
There are magnetically "hard" materials, which remain magnetized, and magnetically "soft" materials, which lose their magnetism after a short time. Permanent magnets are commonly made from materials such as ferrite and alnico. These particular magnets are extremely difficult to demagnetize. This is because they have high coercivity whereas "soft" magnets have low coercivity.