Chemists discuss magnetism in terms of three basic categories: diamagnetism, paramagnetism, and ferromagnetism.

Diamagnetic materials have all of their electrons arranged in pairs, which, by definition, means that their spin magnetic moments must all be arranged in pairs and thus cancel each other out. For this reason, diamagnetic materials cannot be magnetic, and won’t be influenced by magnetic fields.

Paramagnetic materials have unpaired electrons, but in these materials the electrons’ spin magnetic moments cannot all be lined up in the same direction, which means that they cannot be strongly magnetic. Since they do have unpaired electrons, they can be influenced by applied magnetic fields, but not to the same extent as the third class, ferromagnetic materials.

Ferromagnetic materials are the materials that can give rise to the magnets we’re all familiar with. All of the materials that magnets can interact strongly with are ferromagnetic. In these materials, there are unpaired electrons whose magnetic spin can all be aligned in the same direction. Note that just because a material is ferromagnetic doesn’t mean it must be a magnet, but rather just that it has the potential to be magnetized. Take a paper clip, for example; when you first pick it up it’s not a magnet, but you can turn it into a weak magnet by holding a magnet next to it for a short length of time. Some of the most common ferromagnetic substances are those made of iron, nickel, or cobalt.