Text: In a magnetic refrigerator, gadolinium, a rare-earth ferromagnetic metal, plays the role of coolant, staying solid throughout the cycle, while a strong magnet replaces the compressor. The gadolinium concentrates heat when a magnetic field is present, then quickly cools down when the field is removed. Normally, as the gadolinium absorbs heat, it stores some of the energy in the form of increasingly random electron spins. But when a magnetic field is applied, the atoms' magnetic moments align themselves in parallel with the magnetic field, regularizing electron spin. Energy is squeezed out of the system, and can be removed by means of a heat transfer fluid. All ferromagnetic compounds evidence this magnetocaloric effect to some degree, but most do so only within a narrow temperature range. A most efficient element The research into this application of gadolinium got under way at the Ames Lab in the early 19905, when Karl Gschneidner and Iowa State colleague Vitalij Pecharsky began investigating and tweaking the rare earth's performance. Earlier lab tests had revealed that in the presence of a magnetic field the metal could heat up and cool down more efficiently than any other element. Even more importantly, it exhibited a marked magnetocaloric effect at near room temperatures.

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