Spanish and American physicists studying nanoelectronics, found that size has the same meaning when it comes to forecasting behavior of electrical contacts in the atom thick.
In the new study, published in Nature, physicists at the University of Alicante in Spain and at Rice University in Houston found that the atomic contacts made of ferromagnetic metals such as iron, cobalt and nickel behave differently than those used in modern electronic devices.
“We found that the last atom in the very end of the series behaves differently than we expected,” said study co-author Doug Natelson, associate professor of physics and astronomy at Rice University. “It turns out that changing the size of these metals, we really can change and their properties.”
The study is based on the Kondo effect, one of the most frequently and thoroughly studied the phenomena of magnetic materials. Earlier, at the dawn of electromagnetism, the researchers knew that normal metals such as copper, better conductors of electricity when cooled. But in the 1930 scientists discovered that adding even a small amount of ferromagnetic metals such as iron, neutralizes this rule. In 1960 a Japanese physicist Yuen explained that the Kondo effect: cooling down in normal metals decreases the oscillation frequency of atoms and, consequently, decreases the electrical resistance. Mobile electrons in metals usually have a tendency to change the spin in the opposite direction of the electron spins of magnetic atoms. So at low temperature electron moving in a ferromagnetic impurity, will transpose the spin and deviate from the given course. This explains why even the tiny ferromagnetic impurities can increase the electrical resistance, despite the further cooling.
Scientists did not expect that the Kondo effect will play a role in the wires and contacts, made entirely of ferromagnetic metals such as iron, cobalt and nickel. Chatterjee and Maria Reyes and Carlos Calvo Yuntayd conducted an experiment in the laboratory in 2008. Calvo, a graduate student, worked with ferromagnetic contacts, the thickness of an atom, which were created by lowering and raising the tip of a scanning tunneling microscope on the surface.
Yuntayd knew Natelson worked with systems of similar size, but manufactured in another way by laying on a flat metal surface. So Yuntayd agreed with the Government of Spain to travel grants, and Natelson agreed to observe the study, which was to spend Calvo at the University of Rice.
“Reyes has acted very quickly, and within a few weeks she has mastered a technique to make a connection to the atomic width,” said Natelson. “She conducted numerous experiments on the joints, made of cobalt and nickel, and we finally saw the same Kondo effect, which she watched in Spain.”
Chatterjee and Joaquin Fernandez-Rossier and Juan Jose Palacio from the University of Alicante, as well as David Jacob of the University of Rutgers, led a theoretical basis for explaining the unexpected effect. Natelson said that this discovery – the latest example of the unique effect that characterizes the field of nanotechnology.
“The engineers, designing something on the atomic level, must remember that there shall come into force very different effects,” concluded Natelson.
