Origin of the spin Seebeck effect
Andreas Kehlberger (Institut für Physik)

The spin Seebeck effect (SSE) presents a novel spin caloric effect which possesses promising properties for spintronic and thermoelectric applications. Currently the effect leaves open questions about its origin and dependences.
In this talk, we present a comprehensive study of the SSE in insulating magnetic garnets providing answers to its controversially discussed origin. Our study covers the dependence of the SSE on the thickness of the ferromagnetic material, the temperature, the magnetic strength field, the interface and the detection material as well as combinations of the afore mentioned parameters. We observe a characteristic saturation of the SSE with increasing thickness, depending on the absolute system temperature of the used ferromagnetic material. Furthermore we find the occurrences of a thickness, temperature, and magnetic field dependent peaking of the SSE signals if probed as a function of temperature, which can be shifted to different temperatures by the detector material. Additional measurements, performed at high magnetic fields, find a suppression of the SSE signals. All these observed signal features are in agreement with the results of numerical simulations of a magnon based SSE, highlighting that the SSE is based on magnonic spin currents emitted by the bulk of the ferromagnetic material, as shown in Fig.1.[1] To emphasize the complexity of the SSE we present measurements in a so far not investigated ferrimagnetic material, revealing two sign changes of the SSE as a function of temperature. These novel signal features highlight that the SSE originates from a complex interplay of the magnonic modes of the material, strongly depending on the detection material.[2]
[1] A. Kehlberger et al., arXiv:1306.0784 (2013)
[2] S. Geprägs, et al., arXiv:1405.4971(2014)