For a long time, researchers could only make it work with superconducting magnets that had to be cooled to very low temperatures — which made it useful as part of a larger, cryogenic cooling system, but useless for room-temperature situations. In recent years, the development of better magnetocaloric materials and strong room-temperature magnets has allowed the technology to inch slowly forward

http://www.extremetech.com/extreme/176393-ge-develops-high-tech-fridge-magnets-that-could-save-the-world-billions-of-dollars-in-energy-costs