(The) development of high efficient spin thermoelectric device in various ferromagnetic/non-magnetic structures

Abstract

When vertical temperature gradient is applied to ferromagnet (FM)/non-magnetic (NM) bilayer structure, injected spin current from non-equilibrium thermal excitation between FM and NM is converted to transverse electrical voltage via inverse spin hall effect in NM material, which is called by spin Seebeck effect. The spin Seebeck effect is only a piece among various spin thermoelectric effects (STE). Experimentally, spin current injection, related transport manipulation, and spin- or electrical-energies harvesting technologies can be investigated by just measuring the STE voltages in various FM/NM structures, deducing the comprehensive physical understanding comprehensive interaction between heat and spin. Therefore, enhancement of the STE can provide various technologic and academic benefits in spintonics expected as next generation technology. In this thesis, we tried to develop of high efficient STE voltage generation methods via the three different approaches for future practical application of STE, in which two approaches focused on the structural engineering and one focused on newly observed spin thermoelectric physics related with lateral temperature gradient. We introduced the new structural engineering method by stacking and piling the FM/NM metallic bilayer structure, which expanded the structure along vertical (multilayer structure) and lateral (spin thermopile structure) direction. At last chapter, we newly demonstrate the spin Nernst effect (SNE) experimentally, which is only expected in only few theoretically reports in spin thermoelectric field. Physically, it can induce spin thermoelectric signal from lateral temperature gradient in contrast with previous SSE. As a result, by applying proper temperature condition to FM/NM bilayer, SNE and SSE can affect the STE simultaneously. So existence of SNE and SSE will be quite helpful for future STE-based devices.