The advantage of nanocomposites for magnets is twofold: nanocomposites promise to be stronger than other magnets of similar weight, and they should use less rare-earth metals. What enables better magnetic properties in these nanocomposites is a property called exchange coupling. The physics are complex, but coupling between different nanoparticles in the composite leads to overall magnetic properties that are greater than the sum of the parts.
Exchange coupling can’t happen in pure magnet materials, but emerges in composites made of mixtures of nanoparticles of the same metals that are used to make conventional magnets. “The advantage of stronger magnets is that the machines you put them in can be smaller and lighter,” says Johnson.
GE would not disclose which materials it’s using to make the magnets, or what its manufacturing methods would be, but Johnson says the company will rely on techniques it has developed to work with other metals. The main problem the company faces, says Johnson, is scaling up production to make large magnets—so far it’s only been possible to make thin films of the nanocomposites. The company has about $2.25 million in funding from ARPA-E.
Hadjipanayis reports his group, a multi-institute consortium, has received nearly $4.5 million in ARPA-E funding. It’s possible to make the necessary nanoparticles in small quantities in the lab, but scaling up will be difficult. “They’re very reactive materials,” he says.
The group is experimenting with a wide range of different types of nanoparticles, including combinations of neodymium-based nanoparticles with iron-cobalt nanoparticles. Another challenge is assembling the nanoparticles in a mixture that ensures they have enough contact with each other to get exchange coupling. “It’s one step at a time,” says Hadjipanayis.