Spin current from heat: new material increases efficiency

　　Physicists at Bielefeld University have found a way to use the heat from electronic devices to create energy, applying the heat to generate magnetic signals known as ‘spin currents’.

　　According to researchers it could be possible in the future to use these signals to replace some of the electrical current currently used in electronic components.

　　In a new study, physicists from the University of Greifswald, Gie?en University, and the Leibniz Institute for Solid State and Materials Research in Dresden tested which materials generated this spin current most effectively from heat. Their findings have been published in the research journal ‘Nature Communications’.

　　The Bielefeld physicists are working on the basic principles for making data processing more effective and energy-efficient in the young field of ‘spin caloritronics’ and the study determines the strength of the spin current for various combinations of thin films.

　　A spin current is produced by 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 take two such nanofilms and place a layer of metal oxide between them usually only a few atoms thick. One of the external films is then heated and then electrons with a specific spin orientation then pass through the metal oxide. This produces the spin current.

　　The teams led by Dr. Alexander B?hnke and Dr. Torsten Hübner have tested different combinations of ultra-thin films. ‘Depending on which material we used, the strength of the spin current varied markedly,’ says B?hnke. ‘That is because of the electronic structure of the materials we used.’

　　According to the researchers, magnetic nanostructures with special combinations made up of cobalt, iron, silicon, and aluminium were particularly productive.

　　The study is one of a number of projects in the ‘Spin Caloric Transport’ (SpinCaT) Priority Programme of the German Research Foundation (DFG).