A potential replacement for rare earth magnets has been discovered

University of Cambridge researchers have discovered a new way to create a potential replacement for rare earth magnets.

Working with colleagues from Austria, researchers from the University of Cambridge have found that tetrataenite, a ‘cosmic magnet’ that takes millions of years to develop naturally in meteorites, could potentially be used in place of rare-earth magnets.

Previously, attempts to create tetrataenite in the laboratory depended on extreme and impractical methods, but that will change with researchers’ use of the common element phosphorus. By using phosphorus, there is an opportunity to produce tetrataenite artificially and at scale without special treatment or expensive techniques.

The article entitled ‘Direct formation of hard magnetic tetrataenite in bulk alloy castings,’ will be published in the magazine Advanced Science. Cambridge Enterprise, the university’s commercialization department, and the Austrian Academy of Sciences have applied for a patent for the technology.

Why is it necessary to look for a replacement for a rare earth magnet?

Building a zero-carbon economy requires a supply of high-performance magnets. Currently, the best permanent magnets on the market contain rare earth elements, which despite their name are found in abundance in the earth’s crust.

However, there is a problem in ensuring a reliable supply of rare earths such as China controls most of the world’s production. It was reported that 81% of the world’s rare earths were sourced from China in 2017. There are other countries mining REEs, like Australia, but as geopolitical tensions rise with China, the current supply of rare earths could be at risk.

Professor Lindsay Greer of the Department of Materials Science & Metallurgy in Cambridge explained: “Rare earth deposits exist elsewhere but mining operations are very disruptive as you have to extract a huge amount of material to get a small amount of rare earth .

“Between the environmental impact and heavy reliance on China, alternative materials that do not require rare earths have been urgently sought.”

What are the current problems with tetrataenite production?

One of the most promising permanent magnet alternatives is tetrataenite, an iron-nickel alloy with an ordered atomic structure. The material forms over millions of years as a meteorite slowly cools. This allows enough time for the iron and nickel atoms to arrange themselves in a specific stacking sequence within the crystal structure, resulting in a material with magnetic properties similar to rare earth magnets.

In the 1960s, tetrataenite was artificially formed by blasting iron-nickel alloys with neutrons, allowing the atoms to form the desired ordered stacking. However, this technique is unsuitable for mass production.

“Since then, scientists have been fascinated by getting this ordered structure, but it always felt like it was something very far away,” said Greer, who also led the research.

Over the years, many scientists have tried to produce tetrataenite on an industrial scale, but this has not been possible.

Use of phosphorus as a potential alternative for tetrataenite production

Now Greer and his colleagues from the Austrian Academy of Sciences and the Montanuniversität in Leoben have found a possible alternative that avoids these extreme methods.

The team studied the mechanical properties of iron-nickel alloys containing small amounts of phosphorus present in meteorites. Within these materials was a phase pattern that suggested the expected tree-like growth structure called dendrites.

“For most people, that’s where it would have ended: nothing interesting to see in the dendrites, but when I looked closer I saw an interesting diffraction pattern indicative of an ordered atomic structure,” said first author Dr. Yurii Ivanov, who meanwhile finished the work in Cambridge and is now working at the Italian Institute of Technology in Genoa.

The diffraction pattern of tetrataenite initially looks like the structure expected for iron-nickel alloys, namely a disordered crystal that is not of interest as a high-performance magnet. Ivanov’s closer look identified the tetrataenite.

According to the team, phosphorus allows the iron and nickel atoms to move faster, allowing them to form the ordered stacking required without waiting millions of years. They were able to speed up tetrataenite formation by 11 to 15 orders of magnitude by mixing iron, nickel, and phosphorus in the right amounts. This allowed the material to form within a few seconds with simple pouring.

“The amazing thing was that no special treatment was required. We just melted the alloy, poured it into a mold and had tetrataenite,” Greer said. “The previous view in the field was that you can’t get tetrataenite unless you do something extreme because you would have to wait millions of years for it to form. This result represents a complete shift in how we think about this material.”

Future cooperation with magnet manufacturers

Although this method shows promise, more work is needed to decide whether it is suitable for high-performance magnets. The team hopes to work with major magnet manufacturers to determine this.

The results of this study could change views on the duration of tetrataenite evolution.