The magnetocaloric effect was discovered more than 100 years ago, but it is only recently that the phenomenon has been viewed as a way to make a solid-state refrigerator. The scheme, as explained more or less by Wikipedia, is to use of a strong magnetic field to control the entropy of a sample of material by constraining the orientation of its magnetic dipoles. The stronger the magnetic field, the more aligned the dipoles, corresponding to lower entropy and heat capacity. Keeping the material at a constant temperature with a heat sink while the magnetic field is switched on makes the material lose some energy. When the magnetic field is subsequently switched off, the heat capacity of the material rises again because the degrees of freedom associated with orientation of the dipoles are once again liberated, thereby lowering the overall temperature of anything connected to it.
Researchers from the Lawrence Berkeley National Lab say a magnetic fridge would consume less electricity than today’s fridges, which account for eight percent of a family’s utility bill according to the U.S. Environmental Protection Agency. And, they say, the magnetocaloric effect could also cool laptops more efficiently than battery-draining fans, serve as the refrigerant in vehicle air conditioners, and be used in industrial refrigeration.
The trick is finding alloys that undergo the phenomenon at room temperature and without requiring too much energy. Much of the focus is on alloys that exhibit not just any magnetocaloric effect, but a “giant” magnetocaloric effect, so named because they exhibit a large entropy change.One material getting scrutiny at the Lab is a nickel-manganese-gallium alloy in which copper is added. Researchers there say the alloy’s magnetism weakens and its nickel-gallium bond strengthens when copper is added. Their work doesn’t explain why nickel-manganese-gallium doped with copper boasts a huge magnetocaloric effect. But it fills in some blanks and offers one of the best looks yet of the phenomenon in action.
“If you know what is really happening in an alloy as it undergoes the magnetocaloric effect, then we can begin to think about adding other elements to get an even bigger effect – which is what we’re after,” says Sujoy Roy, a Lab physicist . He hopes to soon expand his research and analyze alloys doped with lanthanide, iron, and silicon.
Berkeley Lab magnetic fridge write up: http://newscenter.lbl.gov/feature-stories/2010/07/02/magnetic-fridge/
Wikipedia magnetic fridge page: http://en.wikipedia.org/wiki/Magnetocaloric_effect