The Heusler project aims to produce permanent magnets that, unlike today's permanent magnets, contain only readily available metals
Strong permanent magnets are indispensable for many technical applications, for example in medical diagnostics, for power generation or for electromobility. At present, alloys containing rare earth metals are used for this purpose. Their resources are limited. Therefore, the researchers of the Heusler project are looking for compounds of the same name in which various mostly non-magnetic metals form a permanent magnetic material.
Sometimes scientific research touches upon big world politics. The Heusler project is an example of this. Scientists from the Max Planck Institute for Chemical Physics of Solids and Microstructure Physics as well as the Fraunhofer Institute for Mechanics of Materials IWM are looking for chemical compounds that can even consist entirely of non-magnetic elements and are still suitable as permanent magnets. Strong permanent magnets are required in electric motors, in magnetic resonance imaging scanners, in wind turbines and for data storage. Such magnets today contain rare earth metals that go by such melodious names as samarium or neodymium. This is exactly where materials science becomes a political issue. Because today almost all rare metals come from China. The excitement in many companies and politicians worldwide was correspondingly great when the country restricted the export of rare earths in 2010 for reasons of environmental protection, as it was called.
Even if China has now lifted the restrictions on exports, the scientists of the Heusler project want to end their dependence on rare earth metals and the Chinese export policy. “We are looking for new permanent magnets made from readily available materials,” explains Claudia Felser, director at the Max Planck Institute for Chemical Physics of Solids in Dresden and one of the coordinators of the research project. “And we don't look for such materials anywhere, but among the Heusler compounds.” Heusler compounds often consist of non-magnetic metals such as manganese, copper, gallium, tin or aluminum. Due to their chemical interaction, these metals can adopt magnetic properties. Magnetic Heusler compounds can also contain magnetic metals such as cobalt, nickel or iron.
Suitable compounds are first simulated and then synthesized
After a combination of different metals, which is not inferior in attractiveness to today's permanent magnets, the scientists are looking very systematically for cooperation. "We first calculate which compounds could have the desired properties," explains Eberhard Groß, Director at the Max Planck Institute for Microstructure Physics in Halle an der Saale. It depends not only on the choice of elements, but also on the exact mixing ratio. The team around Claudia Felser then synthesizes the compounds, which presented themselves promisingly in simulations.
"For soft magnetic connections, the theoretical predictions work very well," says Eberhard Groß. Soft magnetic materials often have a high magnetic moment and can be magnetized and demagnetized even by small magnetic fields. The latter is a welcome feature in many applications, for example in conventional generators, but not in permanent magnets. These are hard magnetic, so can only be magnetized and demagnetized with high magnetic fields. However, hard magnetic materials often only have a small magnetic moment. "We want both: a great magnetic moment that can only be reversed with a strong magnetic field," says Claudia Felser.
For hard magnets, the microstructure is important
This is where Thomas Höche, a scientist at the Fraunhofer Institute for Mechanics of Materials IWM in Halle, and his employees come into play. They are well versed in how the microstructure of a material affects its properties. "Especially with hard magnetic materials, this plays an important role," says Claudia Felser.
A material that can be strongly magnetized with strong magnetic fields, have already found the researchers to Claudia Felser, but it only has a vanishing magnetic moment. As a permanent magnet, the material is therefore not yet suitable. It also contains platinum and gallium and two materials that are not exactly readily available. However, the researchers have already started using this material further metal combinations envisaged that better meet the requirements.
"But it's not just about finding a single material that can replace rare earth permanent magnets," says Claudia Felser. "We want to understand the chemical physics of the Heusler compounds so well that we can adjust their properties specifically." If they achieve this goal, the cooperation partners would not have to fear that a promising combination will be outpaced by the coincidence of another group. Because the systematic search should help them to find the optimal composition themselves. And when they find them, the Fraunhofer colleagues are in demand again. They also have a lot of experience in using materials with economic potential.
Source: http://www.mpg.de/9390334/heusler-permanent-magnet
Text: Peter Hergersberg
