COLUMBUS, Ohio The world's first photo-induced magnetism in a polymer was demonstrated by researchers here at Ohio State University and at the University of Utah, Salt Lake City.
In the experiment, a blue laser raised the magnetism of the polymer by 50 percent; a green laser brought it back to nominal. The pure-research finding, at 75 K (325°F below zero), could lead to room-temperature storage devices, such as hard disks, that could be written at high densities by laser-based read/write heads, the researchers said.
"This opens opportunities for light-controlled magnetic materials, which could lead to new electronic-storage and computer-storage devices," said Joel Miller, a professor of chemistry at the University of Utah.
Miller and collaborator Arthur Epstein, a professor of physics and chemistry at Ohio State, have been working together for 25 years. Other researchers credited in the discovery are Dusan Pejakovic and Chitoshi Kitamura.
Miller and Epstein based the project on a family of magnetic polymers they discovered 10 years ago that did not need to be supercooled. Further study revealed that the mechanism by which magnetism was being achieved involved the molecules' ability to change shape, which would reorient their magnetic poles. From that family of polymers, the scientists have created several new varieties, culminating in the version that exhibits photo-induced magnetism.
Gallon of milk
Though - 325°F sounds chilly for a memory storage device, it is in the same range as "high critical temperature" superconductors and can be supplied by inexpensive equipment, Epstein said: A gallon of liquid nitrogen costs about the same as a gallon of milk, he added.
In that cold environment, the researchers laid down a thin film of powdered Mn-TCNE, made by combining the tetracyanoethylene (TCNE) polymer with manganese ions. "The organic material is the magnet itself," said Epstein.
The team then used a blue laser to elevate the magnetism of the sample to 150 percent of its original state, after which it retained that extra magnetism. Next, they used a green laser to erase 60 percent of the material's newfound magnetism. Subsequent "writing and erasing" with blue and green lasers, respectively, enabled the magnetism to be indefinitely shuttled between the two states. "We are using lasers to read and write, but you can use broadband sources as well," Epstein said.
The write time is "way less than a second," he said, though the experiment was intended merely to prove the concept, not for speed. Epstein said that scientists will now be able to design shape-changing molecules that operate more efficiently at higher temperatures. The team is exploring various chemical compositions to improve the material with funds from the Air Force and the Department of Energy.
An audio recording of reporter R. Colin Johnson's full interview with professor Arthur Epstein can be found online at AmpCast.com/RColinJohnson.