¿ìè¶ÌÊÓƵ

LIGHT-ACTIVATED plastic magnets could replace complex microchips in the smart
cards of the future. And as well as storing your credit rating or banking
history, the new material could do a host of other jobs. The idea is to combine
the easy-to-read nature of bar codes with the vast memory capacity of
microchips. Simple magnetic readers could interrogate the cards, while a quick
flash of laser light updates them with new information—by subtracting your
shopping bill from your bank balance, for example.

This idea is just one potential application of a discovery by Arthur Epstein
at Ohio State University in Columbus, working with chemists at the University of
Utah. The researchers have found a plastic that becomes permanently magnetised
when illuminated by blue light. And the process is reversible: green light wipes
out the magnetism.

Their new magnetic material is a polymer called tetracyano-ethylene (TCNE).
Its long-chain molecules have weakly magnetic chemical groups attached to them,
evenly spaced throughout the material. But when exposed to blue light, the long
molecules bunch up and bring the magnetic groups slightly closer together.

The groups contain electrons whose spins act like inbuilt magnetic dipoles.
Bringing these electrons closer together allows their spins to interact more
strongly, forcing them to line up. This makes the material as a whole more
magnetic. Green light, on the other hand, forces the molecules to expand back to
their weakly magnetic state.

There is, however, just one drawback: the wonder material currently only
works at −200 °C. But if the effect can be made to work at much higher
temperatures, optical computers and micromotors could ultimately benefit from
the technology, say experts.