Scientists have developed a new, lightweight magnet that outperforms all its molecule-based predecessors. The international collaboration that led to this discovery includes a chemist from the University of Bath. The research is described in this week's issue of the top academic magazine, Science.
Magnets are integral to modern life. They are used to store data in computers and are essential components in many devices including space satellites, music speakers, credit cards and fridge doors. But there’s a catch – magnets are made either entirely or partly from heavy inorganic materials that are mined from the earth, and some of these materials are both rare and unevenly distributed across the globe. The need to find alternatives to the common lanthanide-based magnet is therefore rising. The drive to miniaturise devices is also accelerating the demand for new types of magnet.
There are two main categories of magnet: heavy magnets made from metal alloys, and newer, molecule-based magnets that incorporate both metal ions and organic molecules. Organic components add an attractive versatility to a product, as they can result in materials that are more lightweight and less brittle, meaning the finished product will be less likely to crack under stress (for instance, if it is dropped).
The newly discovered magnet is made from a compound containing chromium and the organic molecule pyrazine, and both ingredients are abundant and relatively inexpensive. Furthermore, the magnet can be produced at low temperatures, adding to its eco-credentials.
Significantly, this molecule-based magnet exhibits a strong ‘memory effect’. A computer’s hard drive provides a good example of where memory effect is important. Buried in the device’s hardware is a series of spinning discs coated in magnetic material. Information is recorded onto the surface of these discs as a series of changes in the direction of magnetisation. The stored data can later be read by detecting those magnetic changes. If these changes are not ‘locked in’, the data will be lost. The harder it is to erase information that has been recorded, the stronger the memory effect of the material being used.
The breakthrough magnet has a memory effect that is 25 times higher at room temperature than it is for the most efficient of its molecule-based predecessors. In other words, the new material maintains its magnetic memory better than other organic materials. It even holds its own against inorganic magnets, which will be surprising to some, as magnets made from hard metals generally excel in this area.
As an added bonus, the new magnet functions at temperatures exceeding 240°C. This means information won’t be lost from your device even if you put it in the oven.
“It’s exciting to have found a 2D network of magnetic material that works in a way that’s radically different to any conventional magnet,” said Dr Elizaveta Suturina from Bath’s Department of Chemistry.
Dr Suturina was involved in the project’s quantum chemistry calculations. These help scientists understand the functional properties of the material on the atomic level.
Commenting on the study’s findings, she said: “This is a great achievement in the field of molecular magnetism in terms of the critical temperature (at which the magnet functions) and the coercivity (resistance of the magnetic material to changes in magnetisation).
“But the most important innovation is the way the material was created – that is, the post-synthetic reduction of a known metal-organic framework, which can be applied to other systems, unlocking the potential of molecule-based materials.”
This new work on magnets was led by the Centre National de la Recherche Scientifique (CNRS) in France. Collaborators included the University of Bordeaux and the ESRF (European Synchrotron Radiation Facility in Grenoble). The researchers’ discovery opens up highly promising prospects, which could lead to next-generation magnets complementary to current systems.
Video credit: Rodolphe Clérac