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Exploring Magnetic Materials: ExMaMa Project (FP7-People E.U.)

[2013-2015]

 

In this project, we investigated superhard magnets using recently developed state-of-the-art theoretical tools. The objective of this project was to design magnetic materials that have, at the same time, a high magnetization density (the same order of magnitude of existing rare-earth-based magnets), but with a reduced or zero content of REM.

What are superhard magnets?

The term superhard magnet is a broad term and encompasses several magnets based on rare-earth metals (REM) (Yttrium, Scandium and the fifteen lanthanides). The term super magnet is strictly related to the use of rare-earth elements as their principal constituents. However, we expect that in the short-coming time, the term superhard-magnet will be no longer attached to the use of REM. 

REM superhard magnets were first developed in the late ’70s and ’80s; are the strongest type of permanent magnets ever made, are ferromagnetic, meaning that like iron they can be magnetized, and have Curie temperatures well above room temperature, meaning they can be used effectively at higher temperatures as well. The main advantage they have over conventional magnets (Ba-Ferrites, AlNi) is that their greater strength allows for smaller, thus lighter magnets; but ones that can do the same job and take up less space -requiring less material-. REM-Supermagnets can be broken down into two categories. First, there is the Neodymium-based magnet, which is made from an alloy of Neodymium, Iron, and Boron to form the Nd2Fe14B tetragonal crystalline structure. This material is currently the strongest known type of permanent magnet and was developed in the 1980s. It is typically used in the construction of head actuators in computer hard drives and has many electronic applications, such as electric motors, appliances, and magnetic resonance imaging (MRI). The second type of super-magnet is the Samarium-Cobalt variety, an alloy of Sm and Co with the chemical formula of SmCo5. 

This second-strongest type of rare-earth magnet is also used in electronic motors, turbomachinery, and because of its high-temperature range, tolerance has many applications in heat resistant machinery. The problem concerning these magnets is the presence of rare-earth elements. Mining rare-earths is very polluting, and cheap rare-earths rapidly made china the sole world supplier. It is therefore clear that from an environmental, economic, and political point of view, it is essential to eliminate, or at least to reduce, our dependence on rare-earth metals (REM).

Our results

As seen from the above figure, X-axis represents the saturation magnetization and Y-axis the uniaxial magnetic anisotropy energy. Solid triangles represent the most powerful magnets to know up-to-date and other common ferromagnets. Our prediction (black dot) shows a novel magnetic material (rare-earth free systems) with values comparable to top rare-earth-magnets. The empty triangle is our prediction for the respective material (solid triangle). Furthermore, the predicted Curie temperature for our best candidate is of the order of 1000 Kelvin -with this value, our predicted material is expected to overpass the current NdFeB magnet technology. The synthesis of these new magnets would be investigated by our experimentalist colleagues in Germany and Japan.

The headquarters of the project were at the Theory Department of the Max-Planck Institute of Microstructure Physics in Halle (MPI-Halle) from 2013 to 2015.