New Materials May Reduce or Replace Rare-Earth Elements in Strong Permanent Magnets

Magnets are critical components of some of today's technologies such as smartphones, earbuds, and electric motors. Magnets containing rare-earth elements are among the most powerful available, allowing smaller device footprints. However, their scarcity and the geopolitical climates of the countries where such rare-earth elements are mined often make them difficult to obtain.

A team of scientists from the Critical Materials Institute of Ames Laboratory have identified magnets based on more readily obtainable rare earths, as well as some promising magnets that don't contain these materials at all.

The researchers presented their findings at the American Chemical Society (ACS) Spring 2019 National Meeting & Exposition. ACS, which claims to be the world's largest scientific society, is holding the meeting through Thursday. It features almost 13,000 presentations on a broad range of science topics.

A representative of Ames laboratory held a press conference about these findings at ACS National Meeting and Convention, on April 2. (See the YouTube video below)

https://youtu.be/W55G9a6NbC0

"We have developed new ways to better predict which materials make good magnets," says Thomas Lograsso, Ph.D., who led the team. "Experimentally, we can 'rehabilitate' near-magnet systems, called paramagnets. We start with alloys or compounds that have all the right properties to be ferromagnetic at room temperature. Many times, these materials have high proportions of iron or cobalt."

Paramagnets are materials that are weakly attracted to a magnetic field and are not permanently magnetized. But with the addition of alloys, paramagnets can be transformed into ferromagnets, or regular permanent magnets, like the metal surface of a refrigerator.

Lograsso's team at the Critical Materials Institute at Ames Laboratory found two promising candidates thus far using this "rehabilitative" approach, and both are forms of cerium cobalt: CeCo3 (See image above) and CeCo5. Although cerium is referred to as a rare-earth element, it is very abundant and easy to obtain.

Previous work on CeCo3 revealed that it exhibited typical paramagnetic behavior. Calculations predicted that adding magnesium to paramagnetic CeCo3 could transform it into a ferromagnet.

These predictions were experimentally validated, Lograsso says, and single crystals of the compound were also found to exhibit this property.

CeCo5 is a strong ferromagnet. The researchers combined theoretical calculations with high-throughput experiments to zero in on the exact amount of copper and iron to add that would optimize the compound's ferromagnetism.

With these additives, the team expects that CeCo5 could eventually be used instead of the strongest rare-earth magnets that contain neodymium (Nd) and dysprosium (Dy), thus easing demand for those critical elements. Lograsso and his colleagues continue to study other similar metals that can be added to CeCo5 to further enhance its suitability as a viable substitute for Nd and Dy magnets.

"Replacing rare-earth magnets, which are in high demand, would be ideal, both economically and environmentally," Lograsso says. "Although our modified cerium-cobalt compounds are not as powerful as rare-earth magnets, they could still be highly valuable for certain commercial applications. So, our goal is to match the right magnet material to a specific application -- a so-called 'Goldilocks' non-rare-earth magnet."

For this reason, the group continues to use their approach to optimize the primary characteristics of poor magnets or non-magnets to transform them into alternatives that are entirely free of rare-earth elements. For example, they are now using cobalt to optimize the performance of iron germanium, Fe3Ge. The resulting compound's high magnetization is comparable with the best Nd-based magnets.

They are also applying this strategy to other promising rare-earth-free compounds to selectively improve magnet properties.

Funding for the research came from the U.S. Department of Energy.