Ben Afleck of Balclutha Primary School asks :-

What are permanent magnets made of?

Richard Blaikie, a nanotechnologist at the University of Canterbury, responded.

Being an electrical engineer I know how important magnets are for a lot of the things we do. As well as being fascinating to play with, magnets make motors, electricity generation, and lots of the electronic gizmos you have at home work. We couldn’t do without them in our modern life!

Magnetism was discovered a long, long time ago, and the ancient Chinese and Greeks used a natural mineral called ‘lodestone’ for things like compass navigation. Lodestone, or magnetite, (which is made up of iron oxide crystals) is a mineral that is magnetic on its own, and which can be used to magnetise other common materials, such as iron. Once magnetized, iron can then be used as a permanent magnet, for magnetizing other materials, and so on. I’m sure that you’ve tried this with a bar magnet and paper clips.

Many modern permanent magnets still use iron or steel, for applications like electric motors or generators, as these are cheap and abundant. However, in the millennia since magnetism was discovered the range of materials that can be magnetized has grown, and some of the strongest permanent magnets around today use compounds of so-called ‘rare-earth’ materials (whose rarity will, of course, make them more expensive than iron). One of the strongest permanent magnet materials is N-I-B, neodymium-iron-boron, but this rusts very easily so needs to be protected.

For other applications where high magnetic fields aren’t required other materials are used, including ceramics or even plastics that can be molded into the right shape—often there will be a ceramic magnet inside your radio aerial to make it work properly, or within your cell-phone charger to help it convert mains power to dc current for charging the battery.