Tunneling magnetothermopower in magnetic tunnel junction nanopillars.

We study tunneling magnetothermopower (TMTP) in CoFeB/MgO/CoFeB magnetic tunnel junction nanopillars. Thermal gradients across the junctions are generated by an electric heater line. Thermopower voltages up to a few tens of µV between the top and bottom contact of the nanopillars are measured which scale linearly with the applied heating power and hence the thermal gradient. The thermopower signal varies by up to 10 µV upon reversal of the relative magnetic configuration of the two CoFeB layers from parallel to antiparallel. This signal change corresponds to a large spin-dependent Seebeck coefficient of the order of 100 µV/K and a large TMTP change of the tunnel junction of up to 90%.