Thermally induced spin polarization

• Applicant: Timo Kuschel, Ph.D.
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257844649

The present project 'Thermally induced spin polarization' is proposed within the second period of the SpinCaT priority programme. It is dedicated to alternative detection techniques for thermally induced spin currents and spin polarizations beyond the use of the inverse spin Hall effect in Pt, since it has been shown that proximity effect in Pt may induce parasitic effects. This affects the spin detection for example in longitudinal spin Seebeck effect (LSSE) measurements in metals, where the anomalous Nernst effect (ANE) is also present. These techniques to use are magnetooptic Kerr effect (MOKE), x-ray resonant magnetic reflectivity(XRMR), tunnel magnetoresistance (TMR) and spin Nernst magnetothermopower (SMTP) which will be tested by thermally induced spin currents generated by either spin Seebeck (SSE) or spin Nernst effects (SNE).In 12/2011 the applicant joined the group of Prof. Reiss in Bielefeld and started to investigate the SSE in nickelferrite (NFO) thin films and in permalloy thin films within the SpinCaT project. Together with his coworkers he studied ANE contributions for temperature-dependent SSE measurements for the longitudinal as well as for the transverse geometry (TSSE). The separation for LSSE and ANE was demonstrated as well as the separation of ANE and planar Nernst effect (PNE) from a vanishing TSSE as published in several publications. Further experiments like XRMR were started in order to test the proximity effect of Pt/NFO bilayers and a MOKE based vectorial magnetometry setup was built up in the last months.The present proposal is the first-time proposal for the applicant. It describes in detail, how SSE induced spin polarization will be detected by MOKE in Bi doped NFO and in CoFeTb/Cu/FM trilayers (FM=YIG, NFO, magnetite). The SNE will be shown in platinum films using MOKE, XRMR and TMR. Additionally, the thermally induced spin Hall magnetoresistance which is more correctly the spin Nernst magnetothermopower will be investigated. First experiments are in progress and promise very interesting results.As already in the first periode of the SpinCaT priority programme, this work will be done in close collaboration with partner groups from Garching, Regensburg, Mainz, Kaiserslautern, Osnabrück and Giessen.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1538: Spin Caloric Transport (SpinCaT)