Refrigerator magnets

The magnets cluttering the face of your refrigerator may one day be used as cooling agents, according to a new theory formulated by MIT researchers. The theory describes the motion of magnons - quasi-particles in magnets that are collective rotations of magnetic moments, or "spins." In addition to the magnetic moments, magnons also conduct heat; from their equations, the MIT researchers found that when exposed to a magnetic field gradient, magnons may be driven to move from one end of a magnet to another, carrying heat with them and producing a cooling effect.      "You can pump heat from one side to the other, so you can essentially use a magnet as a refrigerator," says Bolin Liao, a graduate student in MIT's Department of Mechanical Engineering. "You can envision wireless cooling where you apply a magnetic field to a magnet one or two meters away to, say, cool your laptop." In theory, Liao says, such a magnetically driven refrigerator would require no moving parts, unlike conventional iceboxes that pump fluid through a set of pipes to keep things cool. Liao, along with graduate student Jiawei Zhou and Department of Mechanical Engineering head Gang Chen, have published a paper detailing the magnon cooling theory in Physical Review Letters .   "People now have a new theoretical playground to study how magnons move under coexisting field and temperature gradients," Liao says. "These equations are pretty fundamental for magnon transport." A cool effect In a ferromagnet, the local magnetic moments can rotate and align in various directions.