Thermoelectric measurements in magnetic nanowires

The use of non-trivial spin textures such as domain walls and skyrmions holds promise
in future applications like magnetic high-density memories and magnetic logic devices.
Domain walls in perpendicular magnetized nanowires are narrow and can be driven
by spin-torques. Skyrmions due to their particular non-trivial topology makes them
to be robust against external perturbations, are small in size and can be driven in
the same manner as domain walls with spin-torques. The precise detection of position
and motion of these non-trivial spin textures is crucial for future applications. Usually
the detection and characterization are performed electrically by their signature in the
anomalous Hall effect (AHE), among other magneto-resistive effects. In the case of the
AHE the detection is limited to Hall crosses and an electrical current is needed for the
detection.
The results in this work show that thermoelectric effects such as the anomalous Nernst
effect (ANE), which is the thermoelectric analogue of the AHE, allows a non-invasive
measurement, detection of the position, the counting and the characterization of nontrivial spin textures. By using domain detection and observation techniques such as
magneto optical Kerr microscopy and magnetic force microscopy the presence of the
non-trivial spin structures in the devices is corroborated. Not only the presence of the
non-trivial spin textures is verified, but also the ANE based detection is demonstrated.
This allowed to detect with nanometer precision the movement of domain walls and
the signature of individual skyrmions in the devices. Furthermore, a new procedure,
the “two-heater” procedure, is presented which allows to separate the contributions of
the different thermal gradients to the total measured thermoelectrical signal. It can be
used to remove signal contributions arising from unwanted thermal gradients.