Physicists find new explanation for key experiment
Researchers at Bielefeld University publish findings on spin caloritronics and are the first to apply measurement methods in the field
An experiment at Tohoku University (Japan) in 2008 laid the foundations for research on ‘spin caloritronics’ – a field that aims to develop more effective and energy-saving data processing in information technology. Since then, many new spincaloric effects have been studied, but the key experiment in Japan could not be replicated. Researchers at Bielefeld University’s Faculty of Physics have now found an explanation for this. They have published their findings in the journal Nature Communications. By applying a new measurement method available at major research facilities, they have also extended the experimental repertoire in spin caloritronics. These results can be found in the journal Physical Review Letters.
The scientists at Bielefeld are generating pure spin currents in magnetic materials that do not conduct electric current – so-called magnetic isolators. They are doing this with thin magnetic films made of nickel ferrite or iron garnet. ‘Just as you can use electric current to build up an electric voltage in materials that conduct electricity, you can use a spin current to build up a spin voltage in magnetic isolators. This is called spin accumulation,’ is how Dr. Timo Kuschel describes the parallels between classic electronics and spintronics. Kuschel is responsible for the spin caloritronics team in the research group headed by Günter Reiss. In the reported experiment, the team has now shown that thermal spin currents can be generated through differences in temperature. However, their explanation and their effect differ from what was originally anticipated. ‘Nonetheless, the true effect is a very effective means of generating thermal spin currents. That is why we are naturally still very thankful to our Japanese colleagues for their research. It was the first experiment worldwide that got the ball rolling in the field of spin caloritronics,’ says Günter Reiss. He is carrying out the experiments in cooperation with Universität Regensburg, the Walther-Meissner-Institute in Garching, and the Center for Materials for Information Technology in Alabama (USA).
In this experimental design, the sample is stretched between two copper blocks. One is hot; the other, cold. The coils generate the magnetic field; the contact pins measure the tension. Photo: Bielefeld University
For Timo Kuschel, it is very clear that ‘the findings ensure the need for further discussions and research in the field of spin caloritronics.’ Together with Dr. Andy Thomas and Dr. Jan-Michael Schmalhorst, the team managed to obtain 800,000 Euro of research funding last year for projects in the German Research Foundation’s (DFG) priority programme ‘Spin Caloric Transport’ (SpinCaT). The new findings support the research in the SpinCaT priority programme that was set up in Germany in 2011 and granted a further three years of funding in 2014.
D. Meier, D. Reinhardt, M. van Straaten, C. Klewe, M. Althammer, M. Schreier, S.T.B. Goennenwein, A. Gupta, M. Schmid, C.H. Back, J.-M. Schmalhorst, T. Kuschel, and G. Reiss: Longitudinal spin Seebeck effect contribution in transverse spin Seebeck effect experiments in Pt/YIG and Pt/NFO, Nature Communications 6, 9211 (2015), www.nature.com/ncomms/2015/150923/ncomms9211/full/ncomms9211.html
T. Kuschel, C. Klewe, J.-M. Schmalhorst, F. Bertram, O. Kuschel, T. Schemme, J. Wollschläger, S. Francoual, J. Strempfer, A. Gupta, M. Meinert, G. Götz, D. Meier, and G. Reiss: Static proximity effect in Pt/NiFe2O4 and Pt/Fe bilayers investigated by x-ray resonant magnetic reflectivity, Physical Review Letters 115, 097401 (2015)¸ dx.doi.org/10.1103/PhysRevLett.115.097401
Further information is available online at:
Prof. Dr. Günter Reiss, Bielefeld University
Faculty of Physics
Telephone: 0521 106-5411
Dr. Timo Kuschel, Bielefeld University
Faculty of Physics
Telephone: 0521 106-5423