Universities Develop Light-Tunable Plastic Magnet
Brian Dance, Contributing Editor -- Semiconductor International, 6/1/2002
The world's first light-tunable plastic magnet has been demonstrated by researchers at Ohio State University (Columbus) in collaboration with the University of Utah (Salt Lake City). The plastic material becomes 1.5× more magnetic when irradiated with blue light. Green light partially reverses this photo-induced magnetism.
The magnet consists of the polymer tetracyanoethylene containing manganese ions; it can be deposited as a thin film. A six-hour irradiation with 488 nm blue light with 50 mW/cm2 intensity from an argon ion laser puts the thin film of the material into its more highly magnetic state. The green 514 nm line from the laser reverses the effect somewhat, so that the magnetism decreases to 60% of the normal value. The light-sensitive magnet will only function at temperatures below 75 K, a temperature at which superconductivity can be obtained. Thus, instead of irradiating the film with green light, the magnetism can be reversed by allowing the temperature of the magnet to rise above 250 K.
The researchers believe that the blue and green light cause the molecules of the material to change into two different shapes. "Once one molecule in the magnet locks into a different shape, its magnetism changes and it encourages its neighboring molecules to change shape too," said Arthur Epstein, professor of physics and chemistry, and director of Ohio State's Center for Materials Research. During the magnetization of the plastic material, electrons are pushed into a metastable state so that the material remains magnetized when the light is removed. The researchers claim that the magnetism can remain for up to 11 days.
Magneto-optical systems can, at least in theory, operate more rapidly and more efficiently than conventional electronic circuits. Light-tunable magnets may enable computers to write and erase data magnetically
The researchers are now trying to improve the magnet by exploring various chemical compositions. In particular, Epstein would like to make a magnet that will show the photo-induced magnetism at higher temperatures, enabling it to eventually become commercially viable. He would also like more control over the colors of the light that produces the changes.
The Air Force Office of Scientific Research and the U.S. Department of Energy funded this work.
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