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Magnets Meddle With Melting

10 December 2004 (All day)
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Melting mystery. Physicists aren't sure why a strong magnetic field raises the melting point of ice as much as it does.

In a strong magnetic field, ice melts at a higher temperature than normal, a team of physicists has discovered. The effect is tiny--no household magnet is going to stave off the thawing of your freezer contents in a power failure - but is still a thousand times more than theory predicts.

With water, water everywhere, one might be forgiven for thinking that scientists unraveled all its secrets long ago. But water "is a system full of surprises," says Caltech physicist Kenneth Libbrecht. The latest of those surprises comes from Hideaki Inaba and his colleagues at Chiba University in Chiba, east of Tokyo, who studied the effect of strong magnetic fields on the melting point of ice. Using a refined version of a technique called differential scanning calorimetry, the team monitored the temperature difference between the sample and a reference material as the pair were slowly warmed. As the ice started to melt, it absorbed energy, giving rise to a telltale temperature difference flagging the melting point.

In the presence of a strong 6 Tesla magnetic field--about four or five times stronger than the magnetic field inside a standard hospital MRI scanner--the team found that ice's melting point increased by 5.6 millikelvin, they report in the 1 December issue of Applied Physics. This result was a surprise: thermodynamic theory predicts a shift a thousand times smaller. Inaba believes the answer may lie in the magnetic field's influence on the vibration and rotation of water molecules, which he argues stabilizes the ice and hikes the temperature needed to melt it.

"It looks like an interesting result, and is worth trying to understand," says Libbrecht. Inaba's work follows the recent discovery by Seiichiro Nakabayashi and his colleagues at Saitama University in Japan that water's ability to bend light is also influenced by powerful magnetic fields. The two effects may well be related, speculates Inaba. Now the researchers need to come up with a theory that explains them both, says Libbrecht. "Until you have some theory to pin on it, you just put it on the wild-and-interesting-phenomena shelf," he says.

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