• Question: Why are some metals magnetic but others aren't?

    Asked by Meg to Chris, Josh, Rebecca, Rob, Susan on 17 Jun 2015.
    • Photo: Susan Cartwright

      Susan Cartwright answered on 17 Jun 2015:

      Magnetism arises when an element has unpaired electrons: the electron spin makes it respond to magnetic fields (paired electrons have opposed spins, and the magnetic effects cancel out).

      In some elements with unpaired electrons, neighbouring atoms tend to align their electron spins. This is what makes a metal a ferromagnet (i.e. magnetic in the everyday sense). In other elements, this interatomic interaction isn’t strong enough to line up the spins, so although the individual electrons respond, the response cancels out with nearby atoms to produce no net effect. These elements are not magnetic. Neither are elements with no unpaired electrons, such as carbon.

    • Photo: Rebecca Dewey

      Rebecca Dewey answered on 18 Jun 2015:

      In addition to what Susan says, which is totally correct, you can create a magnet using a coil of electrical wire. The electromagnetic force works in just the same way as with Susan’s ferromagnet, but only when there is an electric current passing through the wire coil. There are some metals that only become magnetic when a very large electric current is passed through them. We cool these magnets down very cold, so the atoms jiggling around don’t slow the electron current down (superconducting state), and then pass a very large amount of electricity through the metal. In this state, they produce a very large magnetic field, like those used in MRI scanners.

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