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...