4 February 2002

First Light-Tunable 'Plastic' Magnet Developed

by Kate Melville

Low-cost, flexible electronics and better computer data storage might result from the world's first light-tunable plastic magnet, just developed at Ohio State University. With colleagues at the University of Utah, researchers here developed a plastic material that becomes 1.5 times more magnetic when blue light shines on it. Green light partially reverses that effect.

Although possible applications are years away, this technology could one day lead to a magneto-optical system for writing and erasing data from computer hard drives.

While other scientists have developed plastic magnets, and yet others have developed light-responsive magnets, this is the first material to marry both technologies into one - and at record-high temperatures, explained Arthur J. Epstein, professor of physics and chemistry and director of Ohio State's Center for Materials Research.

The magnet functions up to a temperature of 75 Kelvin (about �200�C, or �325�F). This temperature, which approaches that of today's "high-temperature" superconductors, is a key factor for enabling commercial applications for the technology.

The magnet resulted from a 25-year collaboration between Epstein and Joel S. Miller, professor of chemistry at the University of Utah. They describe the magnet in the current issue of the journal Physical Review Letters, in a paper coauthored with Dusan Pejakovic, a doctoral student in physics at Ohio State, and Miller's former graduate student Chitoshi Kitamura, now at the Himeji Institute of Technology in Japan.

Though the working temperature of the magnet is very cold, it represents an important first step toward future light-based forms of electronics, Epstein said.

"Now that we've proven it's possible to make a light-tunable magnet out of an organic, or 'plastic,' material, we can use what we know about organic chemistry to further improve its properties," Epstein said. "We may someday even be able to improve it to the point that it works at room temperature."

The plastic magnet is made from a polymer comprised of tetracyanoethylene (TCNE) combined with manganese (MN) ions -- atoms of the metal manganese with electrons removed.

Epstein and his colleagues deposited the Mn-TCNE powder into a thin film. After they "charged" the material with an initial six-hour dose of blue laser light, the magnet maintained a higher degree of magnetism -- 150 percent of its normal level -- even in the dark.

Green laser light reversed the effect somewhat, by decreasing the material's magnetism to 60 percent of its normal level.

Why would 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 neighbor molecules to change shape, too," Epstein explained.

Worldwide, scientists and engineers are working to develop computer data storage based on light and magnetics. Theoretically, such magneto-optical systems would 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.

Because the new magnet works at temperatures up to 75 Kelvin, it could one day be employed in a device that was cooled by a refrigerator or by liquid nitrogen. Today, liquid nitrogen costs less per gallon than milk -- roughly $2. Manufacturers that bought it in bulk would pay even less.

But such applications are years away, said Epstein. "We'd like to see the magnet work at higher temperatures before we talk about commercial development," he said.

He his colleagues are now trying to improve the magnet by exploring different chemical compositions.