Influence of the thermal interface resistance on the thermovoltage of a magnetic tunnel junction

摘要

In the field of spin caloritronics recent theoretical models suggested a significant influence of the interfaces ofthe magnetic tunnel junction (MTJ) on the thermal transport. In this work magnetothermopower measurementsare carried out on CoFeB/MgO/CoFeB nanopillars and an unexpected increase of the thermovoltage with thediameter of the nanopillars is observed. To understand this behavior the thermal profiles are computed by finiteelement simulations. The observed behavior with the pillar diameter could only be reproduced in simulationsby considering a far lower effective thermal conductivity of the MgO than the intrinsic thin-film value. Inagreement with theoretical predictions, a finite thermal conductivity of the MgO/CoFeB interface can explainthis observation. This is experimental evidence of the influence of the thermal resistance of the MgO/CoFeBinterfaces on magnetothermovoltage measurements and is in agreement with recent theoretical predictions. Themeasured magnetothermovoltage is around 4.5 μV and the simulated temperature difference is about 2 K acrossthe tunnel barrier, which resulted in a magnetic contribution of the thermopower of ΔS_(MTJ) ≈ −2.25 μV K~（−1）.This value was about 20 times smaller than the result obtained by the typically used thermal conductivity of MgOthin films.