Developing an anisotropic version is key to performance. Hadjipanayis’ group is taking a divide-and-conquer approach of separately synthesizing hard and soft nanoparticles that they will then bind together to form magnets. The issue is that exchange coupling is a short-range interaction, effective at distances below 20 nm, so the nanoparticles need to remain at a size compatible with that. If the team can overcome the difficulties, though, the approach has a theoretical energy product of as much as 100 MGOe.
One of the continuing challenges in nanotechnology is manufacturing. The issues are multifold: researchers not only need to find methods to synthesize the nanoparticles, the process needs to be scalable to volume production. Sometimes, the techniques are high tech, but sometimes they're surprisingly lowbrow.
At the University of Texas, physicists have developed a method for fabricating anisotropic bonded magnets using surfactants -- basically, soap. Led by physicist Ping Liu, the group starts with neodymium-iron-boron and samarium cobalt, ball-milling the materials in solution with surfactants to produce high-aspect-ratio nanochips with coercivities as high as 26 MGOe. They mix the chips with organic binders, then press the material together into magnets under a 20-kOe magnetic field. Applying the field helps align the chips to yield anisotropic magnets with energy products of 19.1 MGOe.
Other projects are even more ambitious. At the US Department of Energy’s Ames Laboratory, researchers are working to develop permanent magnets that use cerium, a rare earth element far more available and economical than neodymium. Led by senior metallurgist William McCallum, the team is investigating alloys that could yield temperature-tolerant magnets for electric vehicle motors. They've teamed with Molycorp Minerals LLC, which runs the resurgent Mountain Pass mine in California, as well as General Motors.
Meanwhile, a separate group at Ames Laboratory is collaborating with researchers at the Pacific Northwest National Laboratory to develop a nanostructured manganese bismuth magnet that holds out the prospect of an energy product of 40 MGOe at 200C.
As with all research that explores fundamentally new technologies, these projects will not come to fruition for a long time, if ever. Even removing the economic argument for pursuing alternatives to rare earth permanent magnets, logistical and environmental concerns still make the effort worthwhile. Research like this not only promises a fresh take on magnets, it could be laying groundwork for entirely new technologies and industries.
In part four of this five-part series, we'll look at permanent-magnet motors that use flux focusing in three dimensions to get REE-free performance without the REEs.