Physicists Develop Thin-Film Combinations to Use Waste Heat from Electronic Devices

The heat generated in electronic devices (e.g. computers) is generally wasted. At present, physicists from Bielefeld University have come up with a technique to put the waste heat to good use — they use the heat to produce magnetic signals called “spin currents.”

In the coming years, these signals can function as a substitute for electric current in electronic components. As part of an innovative research, the physicists investigated the materials that had the ability to most efficiently generate this spin current from heat. The study was conducted in collaboration with researchers from the University of Greifswald, Gießen University and the Leibniz Institute for Solid State and Materials Research in Dresden. The outcomes of the study have been published in the Nature Communications research journal on November 20th, 2017.

Dr. Alexander Böhnke, Dr. Timo Kuschel, and Dr. Torsten Hübner (from left to right) are studying a new kind of current that should lead to even tinier and more energy-saving electronic components than those currently available today. CREDIT: Bielefeld University.

The Bielefeld physicists are investigating the fundamental principles for rendering data processing more productive and energy-efficient in “spin caloritronics,” a relatively new field. The researchers are the members of the “Thin Films & Physics of Nanostructures” research team led by Professor Dr Günter Reiss. The new research by the team involves ascertaining the spin current’s strength for different thin-film combinations.

A spin current is generated due to temperature differences between two ends of an electronic component, which is very small with a thickness just one-millionth of 1 mm. As the components are made of magnetic materials (e.g. cobalt, iron or nickel), they are known as magnetic nanostructures.

The physicists chose two such nanofilms and positioned a metal oxide layer between the nanofilms, where the thickness of the metal oxide layer is just a few atoms. One of the external films was heated up, for instance, using a focused laser or a hot nanowire. Then, electrons that have a particular spin orientation pass through the metal oxide, thereby generating the spin current. A spin can be understood to be electrons spinning clockwise or anti-clockwise around their own axes.

In the new research, Dr. Alexander Böhnke and Dr. Torsten Hübner collaborated with their colleagues Dr. Timo Kuschel and Privatdozent Dr. Andy Thomas to investigate various ultra-thin film combinations. Every time, one of the external films was heated in the same manner.

Depending on which material we used, the strength of the spin current varied markedly. That is because of the electronic structure of the materials we used.

Dr. Alexander Böhnke

The researchers depended on theoretical hypotheses to discover appropriate materials that have the suitable electronic structure. The spin current’s measured strength was nearly 10 times greater than that achieved by adopting materials used earlier. The team stated that the magnetic nanostructures with unique combinations formed of iron, cobalt, aluminum and silicon were specifically productive.

The experiments carried out by the physicists from Bielefeld were the fruit of a close collaboration with the group led by Professor Dr. Markus Münzenberg from the Ernst Moritz Arndt University in Greifswald and Professor Dr. Christian Heiliger from the Justus Liebig University in Gießen. Dr. Andy Thomas began his study on this subject at Bielefeld University and is now pursuing it from the Leibniz Institute for Solid State and Materials Research in Dresden.

The research is one of the projects in the “Spin Caloric Transport” (SpinCaT) Priority Programme of the German Research Foundation (DFG). The research group “Thin Films & Physics of Nanostructures” took part in four projects in the program that concluded in June 2017.

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