Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 58: Spincaloric Transport I (jointly with MA)

TT 58.2: Talk

Wednesday, March 18, 2015, 09:45–10:00, H 0110

High tunnel magneto-Seebeck effect — •Alexander Boehnke¹, Marvin von der Ehe², Christian Sterwerf¹, Christian Franz³, Michael Czerner³, Karsten Rott¹, Andy Thomas¹, Christian Heiliger³, Markus Münzenberg², and Günter Reiss¹ — ¹CSMD, Physics Department, Bielefeld University, Germany — ²Institut für Physik, Ernst-Moritz-Arndt-Universität Greifswald, Germany — ³1. Physikalisches Institut, Justus-Liebig-Universität Gießen, Germany

Semiconducting materials are known to have large Seebeck coefficients. This is mainly attributed to the gap in their band structure and the asymmetric position of the Fermi-level with respect to this gap. Accordingly, half-metals with a band-gap for only one spin-channel may have very different Seebeck coefficients for the majority and minority charge carriers. The tunnel magneto-Seebeck effect (TMS) is a powerful tool to investigate such spin-dependent Seebeck coefficients because separate spin-channels can be defined in magnetic tunnel junctions (MTJs).

Here, we probe the spin-dependent Seebeck coefficients of half-metallic Heusler compounds in Heusler/MgO/CoFe MTJs. For Co₂FeSi we found a TMS ratio of 96%, which is much larger than that of CoFeB/MgO/CoFeB MTJs (4%). Furthermore, we found an increase in the mean Seebeck voltage from 30µV in CoFeB to 3mV in Co₂FeSi based MTJs, which agrees with ab initio calculations. We will explain these findings by a Julliere-like model, which also shows the importance of the asymmetric Fermi-level position.