Question

I recently bought some buckyballs, considered to be the world's best selling desk toy. Essentially, they are little, spherical magnets that can form interesting shapes when a bunch of them are used together.

After playing around with these buckyballs for a while, I wondered: "Can these guys ever lose their magnetism?" Then I went a step further and thought, "How are magnets affected by the 2nd law of thermodynamics?"

So, how are magnets affected by the 2nd law of thermodynamics? Do they break down and lose their magnetism over time (like iron rusts over time)?

Answer 1

The second law of thermodynamics - about the increasing entropy - which is apparently what you're talking about - holds for any system. Permanent magnets are no exception.

A ferromagnet may look "more ordered" than a non-magnetic material because the spins are oriented in the same direction, rather than random directions. But physical systems may only try to maximize their entropy among configurations that conserve energy (much like the momentum, charge, and other conserved quantities). For ferromagnets, the configuration with spins oriented in random directions would have a much higher energy - because one reduces the energy by orienting the spins, elementary magnets, in the same direction.

So the spontaneous disappearance of the uniform electrons' spin would violate the energy conservation.

Among the configurations with the same energy, the magnet still tries to maximize its entropy. In particular, the heat is flowing from warmer pieces of the material to colder ones, and so on. More generally, the entropy never goes down, and that's the only general statement that follows from the second law of thermodynamics.

Ferromagnets are not special among physical objects that could have a higher entropy if you allowed the energy to increase. For example, any object would raise its entropy - the amount of disorder - if its temperature increased. But a higher temperature requires a higher energy, too. One can't violate the first law of thermodynamics (energy conservation) just because it would make it more straightforward to satisfy the second law. Both of them hold in Nature.