A light-sensitive plastic magnet that works at record temperatures has been developed by Ohio State University and the University of Utah, offering new opportunities for light-controlled magnetic materials. The new plastic magnet becomes 1.5 times more magnetic when blue light shines on it. Green light partially reverses the effect. Such magnets have potential for new applications in electronic data storage.
A key factor in enabling commercial applications for this technology is that the magnet functions up to a temperature of 75 K. This temperature, which approaches that of today's high-temperature superconductors, represents an important first step towards future light-based forms of electronics.
The plastic magnet is made from a polymer comprised of tetracyanoethylene (TCNE) combined with manganese (Mn) ions. The researchers deposited the Mn-TCNE powder into a thin film. After they "charged" the material with an initial 6 h dose of blue laser light, the magnet maintained a higher degree of magnetism - 150% of its normal level - even in the dark.
Green laser light reversed the effect somewhat, by decreasing the material's magnetism to 60% of its normal level. Why should light have this effect? The researchers think the different wavelengths of blue and green light cause the TCNE molecules to change shape in different ways. Once one molecule in the magnet locks into a different shape, its magnetism changes, and it encourages its neighbouring molecules to change shape too.
Scientists and engineers worldwide are working to develop computer data storage based on light and magnetism. Such magneto-optical systems would theoretically work faster and much more efficiently than traditional electronics. A light-tunable magnet would be a critical component, because it would allow computers to write and erase data magnetically. In a future memory device, information could be encoded in the material as regions of stronger or weaker magnetism, which could be written and erased using tightly focused lasers. This could lead to information storage at very high densities. The organic magnet still has a long way to go, however, before it has the properties demanded of commercial devices.