HOUSTON -- (April 29, 2009) -- Spanish and U.S. physicists studying nanoelectronics have found that size really does matter when it comes to predicting the behavior of electrical contacts that are just one atom wide.
In new research appearing this week in the journal Nature, physicists at Spain's University of Alicante and at Rice University in Houston have found that single-atom contacts made of ferromagnetic metals like iron, cobalt and nickel behave very differently than do slightly larger versions that are on the order of the devices used in today's electronic gadgets.
"We've found that the last atom in the line, the one out there on the very end, doesn't want to align itself and behave like we expect it to," said study co-author Doug Natelson, associate professor of physics and astronomy at Rice. "What this shows is that you can really alter what you think of as a defining property of these metals just by reducing their size."
The findings center on the "Kondo effect," one of the most studied and well documented phenomena in magnetic materials. Scientists learned early in the study of electromagnetism that normal metals, like copper, conduct electricity better as they became colder. But in the 1930s, scientists found that adding even trace amounts of ferromagnetic metals like iron would throw off this effect. In the 1960s, Japanese physicist Jun Kondo explained the effect: while cooling normal metals results in fewer vibrations among atoms, and thus less electrical resistance, mobile electrons in the metals tend to align their spins in the opposite direction of the spins of electrons in a magnetic atom. Thus, at low temperatures, an electron moving past a magnetic impurity will tend to flip its spin and therefore get deflected from its path. This explains why even tiny magnetic impurities can cause electrical resistance to rise, in spite of further cooling.
Based on decades of experimental evidence, physicists wou
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