Researchers see Rare Earth Like Magnetic Properties in Iron

Researchers discovered rare earth like magnetic properties in iron that may provide a new and more available ingredient for electric motors and generators.

Recently, researches at the DOE’s Ames Laboratory recognized rare earth magnetic properties in iron. A new iron based compound was observed with the magnetic properties appearing when the compound was positioned between two nitrogen atoms.

Although it’s too soon for any kind of industrial revolutionary products, it does mean the possibility exists that manufacturers can use iron for both permanence and magnetism in high-strength permanent magnets, used in applications such as permanent magnet motors.

In modern magnets, iron gives most magnets their strength, and comes with the benefits of being abundant and cheap. But the magnet recipe must also include rare earth elements, which lend magnets “permanence,” or the ability to keep the direction of the magnetic field fixed (also called anisotropy). The challenge is rare-earths materials are expensive and at risk of domestic supply shortages. So, ideal next-generation permanent magnets will rely more heavily on iron or other abundant materials and less on rare earths.

“The breakthrough here is that we see magnetic anisotropy normally associated with rare earths ions in iron,” said Paul Canfield, Ames Laboratory physicist. “This isn’t an industrial breakthrough at this point because these magnetic properties only reveal themselves at cryogenic temperatures. But, it’s a basic science breakthrough that hopefully will point the way to future technical breakthroughs.”

The research group that made this surprising discovery is known for the characterization of new and promising materials, among many things. The key ingredient in this instance is using nitrogen.

“Using nitrogen in solution growth had not yet been well explored because, since we typically think of nitrogen as a gas, it’s challenging to get into a solution” said Jesche, “But we found that lithium — lightest solid element — looked like it could hold nitrogen in solution. So, we mixed together lithium and lithium-nitride powder, and it worked. It created a solution.”

Then the group added in iron and, to their surprise, the iron dissolved.

“Usually iron and lithium don’t mix,” said Canfield, who is also a Distinguished Professor of physics and astronomy at Iowa State University. “It seems adding nitrogen to the lithium in the solution allows iron to go in.”

The rare earth like properties wasn’t the only thing that surprised the researchers.

The resulting single crystals of iron-substituted lithium nitride yielded even more surprises: the opposing external field required to reverse magnetization was more than 11 tesla, as much as an order of magnitude larger than that of commercially available permanent magnets and two or more orders of magnitude larger than is typically found in single crystals. Further evidence of iron’s exotic state in this compound is the field-induced quantum tunneling found for very diluted iron concentrations at the relatively high temperature of 10 Kelvin, a temperature orders of magnitude higher than what had been seen before.

“With detailed measurements, we saw that these single iron ions are indeed behaving like a single rare-earth ion would,” Canfield continued. “And we believe this has to do with the special, fairly simple, geometry that the iron finds itself in: one iron atom positioned between two nitrogen atoms. We hope this crystal growing technique and this specific material can be a model system for further theoretical study of these rare-earth-like iron ions. As it stands, these materials have clear implications on finding rare-earth-free replacements for permanent magnets — and perhaps also may impact data storage and manipulation in quantum computer applications.”

Again, although it’s way too soon for any tangible products and procedures, hopefully discoveries such as this will help eliminate China’s stranglehold on exporting rare earth metals.