Magnets attract certain kinds of metal because they generate fields of magnetic force. Some materials, like magnetite, generate these fields naturally. Other materials, like iron, can be given a magnetic field. Magnets can also be made out of coils of wire and batteries. Cold temperatures will affect every kind of magnet.
Where Magnetic Fields Come From
Magnetic force fields are created by electricity. Every electrical current creates its own magnetic field. The atoms of permanent magnets are full of electric currents lined up to generate large magnetic fields. Electromagnets get their fields from an electric current running through a coil of wire.
Cold and Permanent Magnets
When a permanent magnet is cooled, its atoms don't randomly move as much. This makes them easier to line up and increases their magnetic fields.
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Cold and Electromagnets
Electromagnets also increase their magnetic fields in the cold. In their case it is because cold lowers the resistance of the wire, increasing its current.
Superconducting wire can be used to make electromagnets, which can generate super powerful magnetic fields if their temperatures are low enough.
The effect of cold temperatures on magnets is rather small. Even on cold days they are only a few percent stronger.