Boosting Magnetic-Refrigerant Materials

Several groups of researchers around the world are developing magnetic-refrigerant materials, reports Science News. When the material is exposed to a magnetic field, the field forces the spins of electrons within the material to align and the material heats up. Removing the field permits the electrons to relax into less-ordered states, and the material cools down. By cycling the material through these hot and cold states and venting away the heat, the system can generate an overall cooling effect.

Researchers at the Department of Energy’s Ames Laboratory in Iowa and the Astronautics Corp. of America in Madison, Wisconsin, have created a prototype magnetic refrigerator that operates at room temperature. The Ames group has also developed a new magnetic-refrigerant material that produces the largest cooling effect of any material to date. The material is a combination of gadolinium, germanium, and silicon.

According to Robert Shull at the National Institute for Standards and Technology in Gaithersburg, Maryland, researchers can’t yet take full advantage of this new material. Each time a magnetic field is applied to the material, it shifts the arrangement of atoms, changing the material’s crystal structure and releasing energy, thus reducing the cooling efficiency.

To eliminate these losses, Shull and his colleagues added iron to the gadolinium-germanium-silicon compound. With just 1% of all the atoms in the material consisting of iron, the material no longer changed its crystal structure when exposed to a magnetic field. However, it retained its magnetic-cooling properties and reduced the material’s energy losses by almost 95%.

Shull says magnetic-cooling systems could have uses beyond refrigerators. “One of the things that is really limiting the development of all-electric cars is the fact that they don’t have an air conditioner,” he says. “An efficient magnetic-cooling system could solve that problem.”