Magnets

Everyone collects things: pet rocks, shot glasses, Shmooints…Some people like to collect magnets and stick them all over their fridge. Magnets can be fun, fancy, frivolous, and even useful, but how do magnets work, exactly?

Some matter becomes magnetized when exposed to a magnetic field, meaning it consists of tiny magnetic dipoles, each with magnetic moments, m = IA. These dipoles will all align with each other in the same direction as the field surrounding them. In this way, magnetization is more or less magnetic polarization.

There are several kinds of magnetization, though. There’s paramagnetism, dimagnetism, and ferromagnetism.

Paramagnets are all about unpaired electrons. Paramagnetism refers to the magnetic state of an atom. The spins of unpaired electrons make the atom have magnetic dipoles, which experience a torque under the influence of a magnetic field. Under these conditions, the dipoles tend to align themselves parallel to the field.

Diamagnetism is another magnetic phenomenon. It involves an electron’s orbital speed changing in response to a magnetic field, and forcing their dipole moments to point opposite the magnetic field.

What about permanent magnetization, like the decorations that give life to our otherwise silent refrigerating companions?

There are substances (ferromagnets) that retain their magnetization after the magnetic field is removed. Just like paramagnetism, ferromagnetism involves dipoles created by the spins of unpaired electrons. The difference is that in a ferromagnet, dipoles actually prefer to align themselves in the same direction as every other dipole in a small region. Monkey see, monkey do.

This happens because the electric fields in these atoms don’t cancel out. Now, there are several small regions within a ferromagnet, true, and they may all have different regional orientations. However, as we apply an external magnetic field to a ferromagnet, the material will become magnetized with the magnetic fields of each region aligning themselves with each other. Because of their strong magnetic memories, ferromagnets remain as they were after the external field is dead and gone.

This why our grocery lists stay on the door of the fridge.