Permanent magnets are critical components for numerous devices ranging from electric motors to miniature speakers to disk drives to traction motors for hybrid vehicles to wind generators. The strongest permanent magnets that exist today are based on Nd₂Fe₁₄B, which is a complex metallic system. … Nd₂Fe₁₄B has excellent magnetic properties at room temperature, but poor high temperature performance, and the addition of Dy—a highly critical element—is required for above room temperature applications. Rapidly increasing demand for permanent magnets coupled with supply restrictions and the potential for the ever rising costs of critical elements makes a strong economic case for developing competitive magnets that do not rely on critical elements like Dy.

Here we report the results of an experimental study performed on Ce (the most abundant and low cost rare-earth element) based (Nd_1-x Ce_x)₂Fe_14-yCo_yB nanostructured magnets.

—Pathak et al.

Experiments performed at Ames Laboratory by post-doctoral researcher Arjun Pathak, and Mahmud Khan (now at Miami University) demonstrated that the cerium-containing alloy’s intrinsic coercivity—the ability of a magnetic material to resist demagnetization—far exceeds that of dysprosium-containing magnets at high temperatures. The materials are at least 20 to 40% less expensive than the dysprosium-containing magnets.

This is quite exciting result; we found that this material works better than anything out there at temperatures above 150° C. It’s an important consideration for high-temperature applications.

—Karl A. Gschneidner

Previous attempts to use cerium in rare-earth magnets failed because it reduces the Curie temperature—the temperature above which an alloy loses its permanent magnet properties. But the research team discovered that co-doping with cobalt allowed them to substitute cerium for dysprosium without losing desired magnetic properties.

Finding a comparable substitute material is key to reducing manufacturing reliance on dysprosium; the current demand for it far outpaces mining and recycling sources for it.

The research was supported by the U.S. Department of Energy’s ARPA-E REACT program (Advanced Research Projects Agency-Energy–Rare Earth Alternatives in Critical Technologies) which develops cost-effective alternatives to rare earths. (Earlier post.) The REACT projects identify low-cost and abundant replacement materials for rare earths while encouraging existing technologies to use them more efficiently.

Resources

• Pathak, A. K., Khan, M., Gschneidner, K. A., McCallum, R. W., Zhou, L., Sun, K., Dennis, K. W., Zhou, C., Pinkerton, F. E., Kramer, M. J. and Pecharsky, V. K. (2015) “Cerium: An Unlikely Replacement of Dysprosium in High Performance Nd–Fe–B Permanent Magnets” Adv. Mater. 27: 2663–2667 doi: 10.1002/adma.201404892