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Helium Nanoclusters Retain Full Magnetic Qualities

University of Florida scientists report discovering a curious anomaly of magnetism in an article that appears in the current edition of Physical Review Letters.

While "Novel Magnetism in He3 nano-Clusters" is a textbook example of basic science, it could have implications for nanotechnology, the fast-evolving science of creating ultra small devices for biomedical and other applications, said UF physics Professor Dwight Adams.

"Nanostructures are kind of a hot topic right now, and many scientists are investigating how materials behave at very small sizes," he said. "Our research may have some implications for nonhelium-related nanoclusters that people are pursuing for technical applications."

The subject of the scientists' research is helium 3, which for at least three decades has been scientists' preferred medium for probing magnetic forces because of its extremely low freezing temperature under pressure.

When mixtures containing helium 3 are cooled to near absolute zero, everything except the helium 3 freezes, making it a pure medium for studying magnetism in its "natural," or unpolluted, state.

According to the UF paper, the researchers found that "nanoclusters" of helium 3 atoms have different and previously undiscovered properties than bulk quantities of the same substance. The nanoclusters, tiny chunks of helium 3 as small as 100 atoms across, contain perhaps 1 million atoms, compared with bulk helium 3 containing trillions of atoms.

When subjected to a magnetic force at temperatures within one-thousandth of a degree of absolute zero, atoms in nanoclusters line up in a different pattern than helium 3 atoms in bulk, the researchers found.

Furthermore, while bulk chunks of helium 3 lose 60 percent of their magnetism at low temperatures, the nanoclusters continue to exhibit their full magnetic qualities, the researchers found.

(In both cases, the point at which the atoms line up is known as the "magnetic transition," and their behavior is analogous to a compass needle subjected to the Earth's magnetic field.)

The results are likely to be important to research in nanoscience, including nanocomputing, said Gary Ihas, a UF professor of physics.

Ihas said most computer memory is magnetic. As computers shrink, storing information more densely and retrieving it more quickly, surface effects become very important, he said. Ihas believes these effects may be at the root of the differing magnetic qualities of helium 3 nanoclusters and bulk amounts, he said.

"I am convinced that the unusual magnetism observed by the Florida group is due to a combination of the small number of atoms present and the very large ratio of surface atoms to total atoms," Ihas said. "This effect is the essence of nanoscience, and just the beginning of developments which will quickly impact our everyday lives, which are now so dependent on materials development."

The other authors of the paper are Naoki Matsunaga, a former UF doctoral student; Vladimir Svartz, a postdoctoral associate in the UF department of physics; Jian Sheng Xia, an associate scientist in the UF department of physics; and E.A. Schuberth of the Walther-Meissner Institute in Garching, Germany. - By Aaron Hoover

[Contact: Dwight Adams, Aaron Hoover]






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