If you stick an ordinary piece of metal into a strong magnetic field, it warms up slightly. But some materials do the opposite: they cool down. This is called the magnetocaloric effect, and it's already being used to build future refrigerators without Freon.
In new experiments, researchers took crystals where atoms of rare-earth metals (neodymium, gadolinium, dysprosium, erbium) are arranged in long chains. These chains interact with each other, and inside them electrons can rearrange. It turned out that with changes in temperature or magnetic field, the material can switch: sometimes it cools, sometimes it heats. For three of the four studied compositions, this switch works, but for gadolinium it doesn't, because it has no orbital moment.
This discovery suggests how to tune materials for cooling over a wide temperature range — from cryogenic to room temperature. Perhaps soon we'll have compact magnetic refrigerators that don't hum and don't need a compressor.
The magnetocaloric effect was discovered in 1881 by German physicist Emil Warburg, but it found practical application only a hundred years later, when strong permanent magnets became available.
In Arthur C. Clarke's novel "Childhood's End," aliens use magnetic fields to control the climate — now that's a bit closer to reality.