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Nanotechnology yields transparent magnet.

Scientists searching for new materials have created one that not only exerts a strong magnetic force at room temperature but also conducts light.

Ronald F. Ziolo, a chemist at the Xerox Webster Research Center in Webster, N.Y., and his colleagues made a new version of iron oxide, the stuff of rust, but also -- in a slightly different form -- a coating for audio cassettes and video tapes. Typically, iron oxide absorbs light. But unexpectedly, tiny iron oxide particles measuring 2 to 10 nanometers across become three to 10 times more transparent than the bulk form, the group reports in the July 10 SCIENCE.

Ziolo initially hoped to create transparent magnetic particles for use in duplicating color images. But this nanocomposite works so well that it shows promise as a medium for information storage or as a coolant in magnetic refrigerators, he says.

This material outperforms transparent iron fluoride and iron borate compounds, which are only weakly magnetic. Moreover, the other known transparent magnetic materials work only at extremely low temperatures, says Ziolo.

The small size of the iron oxide crystals leads to the stronger magnetic properties, he adds. Each contains just one magnetic domain, so the crystals stick to a magnet but not to each other. Thus, in a magnetic field, all the magnetic moments line up and work together to create a strong magnetic pull. Larger particles contain multiple domains, so some moments effectively cancel others out, weakening the magnetic properties.

Working with materials scientists from Cornell University in Ithaca, N.Y., Ziolo makes these orange magnetic beads in an ion-exchange resin used commercially as a water softener. "The resin is very critical to giving you the size and type of particle needed," he says. Ziolo thinks this technique will also prove useful for making a variety of new nanocomposites.

First, the researchers add iron to the polymer resin. Next, they oxidize the iron, then wash and dry the particle-laden polymer. By repeating this process nine more times, they can increase the iron content from less than 10 percent to about 40 percent, says Ziolo. With each repetition, the magnetic strength increases because the added iron makes new particles instead of enlarging existing particles.
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Title Annotation:tiny iron oxide particles become more transparent than in bulk form
Author:Pennisi, Elizabeth
Publication:Science News
Article Type:Brief Article
Date:Jul 11, 1992
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