Induced and Permanent Magnets

Why is it that some materials are magnetic and some are not? Why can we stick our magnet to the fridge but not the wall?

Magnets are only attracted to magnetic materials or other magnets. The ferromagnetic materials they are made of are different in atomic structure than other materials.

The atoms inside ferromagnetic materials are individually magnetic and tend to align their fields in the same direction, like putting a group of small bar magnets in a row. This is highly unusual. Most other materials either have no atomic level magnetism or their atoms are entirely misaligned.

The atoms in ferromagnetic materials form large regions called magnetic domains where all the atoms in a domain point their magnetic fields in the same direction.

Typically the domains of ferromagnetic materials are also a jumbled up mess and cancel each other out. However, if an external magnetic field is applied to the material, all of the domains will align and it will itself become a magnet.

Materials that retain their magnetism when the external field is shut off are called permanent magnets. Their domains remain aligned and they don’t need an external field to hold their domains in alignment. Fridge magnets are this type of magnet.

Those that lose their magnetism once the external magnetic field is removed are called induced or temporary magnets. Their domains are only aligned in the presence of an external field and jumble up again when it is switched off. If you touch a paperclip to a permanent magnet its domains will align, but as soon as you remove the nail from the magnet it will lose its own magnetism.