PUB - Publikationen an der Universität Bielefeld

The topic of the doctoral thesis at hand is the tunnel magneto-Seebeck (TMS) effect, which is a textbook example of the emerging research field of spin caloritronics. Spin caloritronics deals with the interplay of charge, heat and spin currents with the goal of developing new data storage techniques or the improvement of existing technologies. In particular, it focuses on the waste heat of today's devices. With the TMS effect it is possible to convert a temperature difference, which extends over several nanometers only, to a measurable voltage based on spin currents. For this, magnetic tunnel junctions are used, which are the foundation of many research areas and applications. In this work, MgAl2O4 (MAO) is investigated as tunnel barrier in comparison to the frequently used MgO. By now, several methods are available to create a temperature difference in tunnel junctions to study the tunnel magneto-Seebeck effect.

Within this work, the laser-induced heating is used in order to compare its results with an intrinsic TMS effect, which is determined by a mathematical symmetry analysis of the experimental results. The most important results of these investigations are the unsuitability of the symmetry analysis with regard to the identification of an intrinsic TMS effect and the material-independent doubling of the switching ratio in case of thick barriers. Due to its low thermal conductivity, MAO presents itself as suitable candidate for the generation of thermovoltages. Furthermore, simulations of the temperature distributions offer new insights into the thermal conductivity of a thin insulating film.

Overall, this work contributes to a fundamental understanding of thermally induced and spin-current based effects in nanostructures and paves the way towards future technical applications.