A short article Héctor G. Riveros and Julián Betancourt was published in The Physics Teacher this month that is quite fun. The paper centers on what happens when compasses interact.

Basically, if the magnetic fields are strong enough and you bring them close enough together, then compasses will influence each other. Ok fine, that’s not so interesting in and of itself until you make use of it. They arrayed lots of compasses together in a hexagonal packing arrangement, all as close as possible to each other.


On the top, the compasses are responding to an external magnetic field.





What’s really cool is when they take the external magnetic field away as you see on the right hand side (or bottom). The compasses form magnetic domains!

This is a really beautiful demonstration of how magnetic materials behave and I bet would make a great tool for teaching. I would not have thought that the magnetic fields produced by individual compasses would be sufficient to cause this kind of interaction.

Now, the next step is to see if you could add temperature to the mix. Given that we’re approximating spins as compasses, then it might be possible to approximate temperature as some sort of small random motion. Take each compass, put it on a small spring (or place small springs between each), and then shake the how ensemble. Eventually the shaking should be enough to cause the compasses to lose their orientation and the magnetic domains will disappear. Voila, you’ve got a Curie temperature.