Aarhus Universitets segl


Magnetic materials are of key importance in a large variety of scientific and technological applications such as data storage,[1,2] biomedicine,[3,4] and electric motors.[5] Tons of high performance rare-earth magnets such as the neodymium magnets are produced every year. However, there are some disadvantages about these types of magnets such as geopolitical circumstances which cause an enormous price increase. Today there is a need for rare-earth free magnets as an alternative to what already exist.

A magnet is not just a magnet. A magnet can be divided into two categories: a soft or a hard magnet depending on how easy the material is to demagnetize when another magnetic field is applied to the magnet. Different applications need different magnetic performance and it is therefore important to develop new and improve existing magnet materials that have a broad interval of magnetic performance.

At CMC we prepare rare-earth free magnetic nanoparticles which improve the magnetic performance compared to bulk magnets.

A well known magnetic materials with unexploited potential

SrFe12O19 is a hard magnet with relatively high theoretical magnetic performance. In the industry the material is produced using a solid-state reaction which means that Sr and Fe compounds are mixed and heated which forcing the compound to react. Another way of preparing SrFe12O19 is by the so called bottom up techniques which means that nanoparticles are produced having magnetic performances closer to the theoretical max. The magnetic properties of nanoparticles highly depend on the particle size. When the size can be controlled, the magnetic performance can be optimized.

One of the challenges by this method is that the particles must be compacted into a pellet or similar. To succeed the nanoparticles must be orientated in the same direction, which is only possible at specific morphologies. For example if the nanoparticles are plates. During compaction the particles will grow because of the heat which results in different magnetic performances. The goal is to produce nanoparticles that have the correct size and morphology – and compact them in a way that gives them the optimal size giving a high magnetic performance

Soft magnets are used everywhere

Another group is the soft magnets. A well known soft magnet is iron. Soft magnets are widely used in a number og different applications such as transformer cores, inductors, electric machines, electromagnet cores, relays, magnetic recording heads.

The size of the CoFe2O4 nanoparticles highly influence the magnetic properties. It is therefore important to control the particles which can be done by changing the synthesis method and synthesis parameters. In situ X-ray diffraction is a method that makes it possible to investigate the particle formation during the synthesis. Thereby, important knowledge about the synthesis rate and growth can be gain. In situ studies are typically done using synchrotrons due to the very intense beam.

Single molecule magnetism

Single molecule magnetism is, as the name suggests, a single molecule that behaves as a magnet. Why is this so special? Magnetic materials you know, such as stick magnets from physics classes, get it’s magnetism from all the atoms interacting with each other, and are therefore fixed (in example, you don’t arrive the next day at physics class, and the north and south pole has suddenly shifted places). There are many molecules that are magnetic, but only a few that keeps its magnetization overnight, and that is the hurdle in single molecule magnetism. So far the best ones work at temperatures around 10K (-263oC) and the goal is to make them work at higher temperatures. The applications of such molecules could be to make hard drives, where every bit is just one molecule, which would increase the storage capacity per area by a factor of around 300! There are also suggestions of using them as quantum bits in quantum computers, which might be the future of extreme super computers!

You may also be interested in

[1] I. Matsui, Jpn. J. Appl. Phys., Part 1, 2006, 45, 8302–8307.
[2]  D. K. Jang and J. H. Chang, Microsyst. Technol., 2013, 19, 1601–1606.
[3] M. A. Riley, A. D. Walmsley and I. R. Harris, J. Prosthet. Dent., 2001, 86, 137–142.
[4] N. R. Routley and K. J. Carlton, Magn. Reson. Imaging, 2004, 22, 1145–1151.
[5] S. Tammaruckwattana and K. Ohyama, presented in part at the IEEE Ind. Elec., Vienna, 2013.