UNL researchers break new ground in spin electronics
University of Nebraska-Lincoln scientists have broken new ground in spin electronics through experiments that prove a magnetoresistance phenomenon on the nanoscale.
Writing 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-sized 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).
This research is significant because it provides the first experimental evidence that a new physical phenomenon exists. This discovery proved Tsymbal's group's earlier theory on quantized magnetoresistance, the researchers said.
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," Sokolov said.
This is all done at a scale of 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. 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. With the aid of a conventional light microscope, one can see objects as small as about 500 nanometers," Redepenning said. "These structures are much smaller."
"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."
It is difficult to predict potential 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 NSF-funded Materials Research Science and Engineering Center at UNL as well as the Nebraska Research Initiative fund this research.
Writing 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-sized 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).
This research is significant because it provides the first experimental evidence that a new physical phenomenon exists. This discovery proved Tsymbal's group's earlier theory on quantized magnetoresistance, the researchers said.
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," Sokolov said.
This is all done at a scale of 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. 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. With the aid of a conventional light microscope, one can see objects as small as about 500 nanometers," Redepenning said. "These structures are much smaller."
"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."
It is difficult to predict potential 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 NSF-funded Materials Research Science and Engineering Center at UNL as well as the Nebraska Research Initiative fund this research.
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