Sweating the small stuff Home

Magnets And Microchips Combine
In A Transparent Supermaterial
IN THE movie Superman, the Man of Steel discovers why he was jettisoned from the doomed planet Krypton by watching a video message stored on a transparent crystal. Now, more than 20 years on, Japanese scientists are working on a revolutionary new semiconductor that might one day be turned into just this kind of gadget.

Computer displays made of the material will have all the image processing and memory circuits invisibly buried in the screen itself, making them cheaper and less power hungry than today's displays.

A team led by Yuji Matsumoto of the Tokyo Institute of Technology (Titech) in Yokohama were looking for a material that was both a semiconductor and a permanent magnet, or "ferromagnet". They succeeded--and were amazed to find that the material is transparent as well.

Best of all, the new material works at room temperature. "This is a very important step," says Hideo Ohno, a semiconductor physicist at Tohoku University in Sendai. "If it didn't work at room temperature it would be no good for use in everyday applications." Ohno and his colleagues have created a ferromagnetic semiconductor of their own by mixing manganese into gallium arsenide. But their material is opaque, and only works at a frigid 110 kelvin.

To produce magnetic semiconductors that can stand the heat, the Titech team with colleagues from the National Institute for Research in Inorganic Materials in Tsukuba turned to a technique called combinatorial chemistry. They carried out thousands of tiny chemical reactions simultaneously in a vacuum, each with slightly different ingredients. They then screened the products of the different reactions en masse to see which had the best properties.

Matsumoto and his colleagues will soon report in Science that one of the reactions produced a thin film of titanium dioxide doped with just under 8 per cent cobalt. This transparent material turned out to be both semiconducting and permanently magnetic at room temperature. Using magnetic microscopy the researchers found areas in the material where electron spins line up spontaneously to produce magnetism.

The Titech researchers say they don't know why the cobalt has this effect. "We need to accumulate more data," says team member Hideomi Koinuma.

Ohno says the discovery is important in the emerging field of "spintronics", in which engineers hope to harness both the charge-carrying aspects of electrons and their spin, which is the root of magnetism. Because the material is magnetic parts of it could store data in much the same way as a computer hard drive. And as a semiconductor, other parts could process information like the transistors in a microchip.

Ohno says the material will most likely be turned into flat-panel displays which have all their processing and storage circuits invisibly built-in. "Currently, transistors in laptop displays absorb a quarter of the brightness of the backlight. Transparent transistors could solve this."