Karl A. Gschneidner and fellow scientists at the U.S. Department of Energy’s Ames Laboratory have created a new magnetic alloy that is an alternative to traditional rare-earth permanent magnets.
The new alloy—a potential replacement for high-performance permanent magnets found in automobile engines and wind turbines–eliminates the use of one of the scarcest and costliest rare earth elements, dysprosium, and instead uses cerium, the most abundant rare earth.
The result, an alloy of neodymium, iron and boron co-doped with cerium and cobalt, is a less expensive material with properties that are competitive with traditional sintered magnets containing dysprosium.
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 percent cheaper 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,” said Gschneidner. “It’s an important consideration for high-temperature applications.”
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 idea behind it is over 100 years old
DYSPROSIUM and neodymium are not exactly the best-known elements in the periodic table, but for makers of high-end electric motors they have become vital. Both are strongly magnetic and thus crucial to the construction of powerful motors of the sort used, for example, in electric cars. Unfortunately, they lurk in the part of the table known as the rare-earth metals and, as that name suggests, workable deposits of them are scarce. At the moment, the main source of supply is in China, whose government has used its near-monopoly to restrict availability and push up the price. So there is a lot of interest in inventing motors that can do without them. And several groups of researchers think they have come up with one.
The device in question is known as a switched reluctance motor. The idea behind it is over 100 years old, but making a practical high-performance version suitable for vehicles has not been possible until recently. A combination of new motor designs and the advent of powerful, fast-switching semiconductor chips, which can be used to build more sophisticated versions of the electronic control systems required to operate a reluctance motor, is giving those motors a new spin.
One of the leading contenders is Inverto, a research and development company based in Ghent, Belgium. Inverto’s engineers, led by John De Clercq, the firm’s research director, are collaborating with the University of Ghent and the University of Surrey, in Britain, and also with an unnamed carmaker. They already have a motor running in a car. At Newcastle University, also in Britain, researchers are working with several companies to produce reluctance motors for both cars and lorries. And studies are being carried out in America and Japan too. A team led by Nobukazu Hoshi of the Tokyo University of Science, for example, has experimented with a reluctance motor in a Mazda sports car.