How does a magnet work?
Short answer: every electron behaves like a tiny magnet (because of its spin). In most materials these tiny magnets point in all directions and cancel each other out. In a permanent magnet they largely point in the same direction, locked in place by the crystal structure. Together they form a magnetic field with a north and a south pole. That field attracts ferromagnetic materials (iron, steel, nickel, cobalt) and attracts or repels other magnets.
Step by step: from atom to magnet
- Electrons: every electron has a magnetic moment due to its spin. In atoms such as iron, cobalt and neodymium these moments do not fully cancel out; such an atom is itself a small magnet.
- Domains: in ferromagnetic materials, neighbouring atoms align with each other spontaneously, in regions a few micrometres in size: magnetic domains (Weiss domains).
- Unmagnetised: in an ordinary piece of iron the domains point in different directions. From the outside you notice nothing.
- Magnetising: a strong external field turns all domains the same way.
- Permanent: in soft iron the domains fall back afterwards, but in a permanent magnet the crystal structure holds them in place. How well that works is called coercivity.
Why does a magnet attract steel?
Steel is not a magnet itself, but it is ferromagnetic. When it enters the field of a magnet, the domains in the steel temporarily align with that field. The steel then becomes a (temporary) magnet itself, with an opposite pole facing the magnet, so they attract each other. Remove the magnet and the steel largely falls back.
Which materials does a magnet work on?
| Yes (ferromagnetic) | No or hardly |
|---|---|
| iron, steel, cast iron | aluminium, copper, brass, zinc |
| nickel, cobalt | gold, silver, lead, titanium |
| ferritic stainless steel (for example 430) | austenitic stainless steel (304, 316) |
| some coins with a steel core | wood, glass, plastic, paper |
Aluminium and copper are not magnetic, but a moving magnet does induce eddy currents in them that slow it down. If you drop a neodymium magnet through a copper tube, it falls remarkably slowly.
Why is neodymium so strong?
The compound Nd₂Fe₁₄B combines a lot of iron (high magnetisation) with neodymium, which strongly locks the magnetisation in one crystal direction. As a result, neodymium has the highest energy density of all permanent magnets: 5 to 10 times more than ferrite. See how strong is a neodymium magnet?
Permanent magnet or electromagnet?
- Permanent magnet: always works, without power. Examples: neodymium, ferrite, AlNiCo, samarium cobalt.
- Electromagnet: a coil with an iron core that is only magnetic when current flows. Can be switched on and off, for example in relays, door locks and lifting magnets.
Frequently asked questions
Can a magnet lose its strength through use?
No, a magnet does not consume energy when it holds something. See why do magnets lose their strength?
Why does a magnet always have two poles?
Because the field consists of closed loops: it comes out of the north pole and goes back into the south pole. If you break a magnet in half, you get two magnets, each with a north and a south pole.
Read also
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