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from the issue of March 1, 2007
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Scientists report breakthrough in spin electronics
BY KELLY BARTLING, UNIVERSITY COMMUNICATIONS
A UNL research group has broken ground in spin electronics by proving a magnetoresistance phenomenon on the nanoscale.
In the March issue of Nature Nanotechnology, Andrei Sokolov, Chunjuan Zhang, Evgeny Tsymbal, and Jody Redepenning, all from UNL, and Bernard Doudin, a former UNL colleague now of the Institut de Physique et de Chimie des Materiaux de Strasbourg in France, reported quantized magnetoresistance in atomic-size contacts. The UNL researchers are with the Nebraska Center for Materials and Nanoscience and the departments of physics and astronomy (Sokolov, Tsymbal) and chemistry (Zhang, Redepenning).
The researchers said the work demonstrated that a new physical phenomenon exists and proved an early theory on quantized magnetoresistance made by a group that also included Tsymbal.
"As a theorist, I am proud that our theoretical prediction of ballistic anisotropic magnetoresistance published earlier in Physical Review Letters was confirmed experimentally by our colleagues - researchers from UNL," Tsymbal said. "We consider our achievement as the demonstration of a new quantum effect at the atomic scale."
Using an electroplating technique, the team measured the conductance of magnetic metals by examining the electrons moving across tiny constrictions in wires, under the influence of a magnetic field.
"If the constriction is small enough, electrons traverse it without scattering and the conductance becomes quantized - it changes step-wise with the constriction size," Sokolov said. "If the wire is made of a ferromagnetic material, the electron transmission through the constriction varies in a quantized fashion when the magnetization changes its direction. This is what Evgeny has predicted theoretically and what we were able to observe experimentally."
This is all on the scale less than one nanometer, or less than one 50,000th the diameter of a human hair.
"Chunjuan and Andrei had to make the constrictions and measure their properties without the benefit of being able to see them," Redepenning said. "It was only later, with the aid of a Scanning Electron Microscope, that they were able to image the results of their plating efforts and to 'see' the structures that gave the results Evgeny had predicted."
It is difficult to predict what will be the consequences of this discovery for technology, the researchers said.
A key step is to improve the reproducibility of the effect, which requires controllable fabrication of structures consisting of a few atoms. Potentially, the quantized magnetoresistance may be appealing for the future generation of ultra-small electronic devices, such as ultra small magnetic read heads, quantum switches and logic circuits, the researchers said.
The National Science Foundation and the Materials Research Science and Engineering Center supported the collaborative effort.
GO TO: ISSUE OF MARCH 1
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Scientists report breakthrough in spin electronics
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