Making magnetism flip twice, by design.

Novel magnetic materials are out there, waiting to be discovered, but finding them is a hit-or-miss proposition. A Japanese team now reports it may have devised a straight path from theory to materials with specific, desirable traits.

When placed in a magnetic field, some materials develop magnetism with the same polarity, While others develop an opposing field. As described in the Feb. 8 PHYSICAL REVIEW LETTERS, the team created a new powder whose magnetic polarity flips twice as temperature climbs from absolute zero.

Such a double reversal was first reported in another material last year. This time, however, the researchers deliberately chose to make their new substance with the specific trait. "This is the first case of a new magnet predicted by theory," says Kazuhito Hashimoto of the University of Tokyo and Kanagawa Academy of Science and Technology in Atsugi.

By incorporating an assortment of metal ions into a crystalline, chromium-based compound, the researchers cause polarity to flip at 35 kelvins and then flip back at 53 K. Between those temperatures, a negative magnetism takes over as one of the ion types, which aligns atomic spins contrary to an applied magnetic field, outweighs the positive responses of other ions.

The researchers expect their directed design to apply to a chemical family that includes the dye called Prussian blue. The double-flip material, a member of that family, is not likely to find practical use. However, Hashimoto and his colleagues are currently creating other magnetic materials, such as ones that respond to light, with commercial promise.