Positive solutions to Europe’s magnet problem

Magnets are everywhere, from electric vehicles and wind turbines to hard drives and magnetic resonance imaging scanners. The problem is that they contain so-called rare earth elements, 17 highly reactive metals which are becoming increasingly difficult to source.

Rare earth elements such as scandium and yttrium are used in many of today’s high-tech gadgets. However, mining operations are located almost exclusively in China and increased local demand there has led to a severe reduction in exports to the rest of the world.

As a result, European scientists are developing ways to magnetise common metals and alloys by using nanoparticles and innovative manufacturing techniques. The EU-funded REFREEPERMAG project has developed a new technique that can use iron, cobalt and carbon to make useable magnets.

The issue is that materials which have a cubic molecular structure, such as metals, demagnetise easily. In contrast, the elongated molecular structure of rare earths means they can be durably magnetised along one axis. This structural property is known as magnetic anisotropy.

In order to increase the magnetic anisotropy of the metallic elements and create a viable alternative to using rare earths, the project has developed a way to deposit metals onto material that has anisotropic features. That way they can distort the cubic structures into more hexagonal or tetragonal arrangements.

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‘If we can control the microstructure, we can control the magnetic properties.’

‘We have achieved the first magnet in the world based on iron and cobalt nanoparticles exploiting shape anisotropy,’ said Dr Dimitris Niarchos, a senior researcher on the project.

The team has developed a second technique, known as ‘combinatorial material synthesis’, that is unique in the European Union. It involves depositing many small samples of alloys on a thin piece of silicon, known as a wafer, each comprising varying ratios of selected elements, including iron, cobalt and carbon.

‘On one wafer, instead of having one uniform sample, we have hundreds or a thousand in one deposition,’ explained Dr Niarchos. It allows the project to quickly try out lots of different combinations to see what works.

The project, which ends this year, has built a prototype micromotor using the anisotropy-based technique and hopes to do the same thing with magnets produced using combinatorial material synthesis later this year. However they are not aiming for mass production.

‘(The project) is trying to more scientifically understand the processes rather than produce large quantities of magnets,’ explained Dr. Niarchos.

Ferrites

Another group of researchers is using nanotechnology to produce rare-earth-free permanent magnets (which have a persistent magnetic field) with a class of material long ignored in magnetic research: ferrites.

Ferrites are brittle ceramic materials that comprise an iron oxide and a metallic element, in this case cobalt or strontium. ‘Ferrites were discovered in the early 50s, so the question is: why did we not use ferrites?’ said Dr Alberto Bollero, coordinator of the NANOPYME project.

The answer is that rare earths were so cheap during the 1980s and 90s that investment in ferrite-based permanent magnets was not economically viable, until now.

In order to make magnets with ferrites, which produce weak but durable magnets, the project needs to combine them with metals, which produce strong magnets that are easily demagnetised by another magnetic field.

They do it by grinding the metal and the ferrite down into a very fine powder through an ultrafast process, before compressing them together to form a new material combining the best properties of both materials. The strong hybrid magnets that are produced could be used as substitutes for rare earth-based magnets in specific applications.

The important thing is to mix the materials correctly, with control right down to the scale of a nanometre, which is 1 billionth of a metre, in order to obtain the desirable characteristics of both. ‘If we can control the microstructure, we can control the magnetic properties,’ Dr Bollero said.

The project, which ends this year, is planning to use the new magnets to produce an electric bicycle motor. The magnetic components of the motor are currently being prepared, with a public demonstration planned for June this year.

An additional challenge for the makers of rare-earth-free magnets is that they must be able to cope with the high temperatures generated by motors. For example, magnets used in electric car motors and wind turbine generators must withstand temperatures of over 100 degrees Celsius.

The EU-funded ROMEO project is tackling that issue by using a computer database to identify and create several alloys of cobalt, manganese and titanium that could produce a rare-earth-free magnet that operates at that heat.

The project finishes this year, and it is ready to make demonstration magnets for use in wind turbines and electric cars, and begin to produce the materials it has developed on an industrial scale. ‘We are now in the phase of implementing our results together with the industrial partners to the production level,’ said coordinator Professor Spomenka Kobe.