Search for ‘spin current’ materials heats up

Electronic devices such as computers generate heat that mostly goes to waste. Physicists at Bielefeld University in Germany have found a way to utilize this energy, by using it to generate magnetic signals known as ‘spin currents’. In future, these signals could replace some of the electrical current in electronic components.

Now, in a new study, the physicists tested which materials could generate spin currents most effectively from heat. The research was carried out in cooperation with colleagues from the University of Greifswald, Gießen University and the Leibniz Institute for Solid State and Materials Research in Dresden, all in Germany. The researchers report their findings in a paper in Nature Communications.

The Bielefeld physicists, who are members of the ‘Thin Films & Physics of Nanostructures’ research group headed by Günter Reiss, are working on the basic principles for making data processing more effective and energy-efficient in the young field of ‘spin caloritronics’. Their new study determines the strength of the spin current for various combinations of thin films.

A spin current is produced by the differences in temperature between two ends of an electronic component; these components are extremely small and only one millionth of a millimetre thick. Because they are composed of magnetic materials such as iron, cobalt or nickel, they are called magnetic nanostructures.

The physicists took two nanofilms containing these magnetic nanostructures and placed a layer of metal oxide, a few atoms thick, between them. They heated up one of the external films – for example, with a hot nanowire or a focused laser – causing electrons with a specific spin orientation to pass through the metal oxide, producing the spin current. A spin can be conceived as electrons spinning on their own axes – either clockwise or anti-clockwise.

Alexander Böhnke and Torsten Hübner together with their colleagues Timo Kuschel and Andy Thomas, tested different combinations of ultra-thin films. Each time, they heated one of the external films in the same way. “Depending on which material we used, the strength of the spin current varied markedly,” says Böhnke. “That is because of the electronic structure of the materials we used.”

Based on theoretical assumptions, the researchers were able to find suitable materials possessing the appropriate electronic structure. The measured strength of the spin current in these materials was up to 10 times higher than that obtained with previously used materials. According to the researchers, magnetic nanostructures with special combinations of cobalt, iron, silicon and aluminium were particularly productive.

The experiments conducted by the Bielefeld physicists were the product of a close cooperation with the team headed by Markus Münzenberg from the Ernst Moritz Arndt University in Greifswald and Christian Heiliger from the Justus Liebig University in Gießen. Andy Thomas started his research on this topic at Bielefeld University and is now continuing it at the Leibniz Institute for Solid State and Materials Research in Dresden.

This story is adapted from material from Bielefeld University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.