Study on spin thermoelectric effects in ferromagnet/non-magnet structures for spin-caloritronic device applications

Abstract

The spin thermoelectric effect is the phenomenon that the spin current generation through a difference in spin potential due to a thermal gradient. When a thermal gradient generated in the magnetic layer, a spin current can be obtained The spin current can be injected into the nonmagnetic layer to generating the electric current via the inverse spin Hall effect

spin Seebeck effect. Those spin thermoelectric phenomena are expected as future thermoelectric devices because they have the potential to overcome the limitations of the Wiedemann Franz law. In this paper, we studied and focused how to use this spin thermoelectric phenomenon through three topics. First, we studied the increase of the efficiency of the spin thermoelectric effect for energy harvesting. The spin thermoelectric efficiency is still small compared to the general thermoelectric, In this study, the amplification of the spin thermoelectric signal was demonstrated by integrating the multilayer and spin thermopile structures. Second, we proposed a method of utilizing the spin Nernst effect in spin orbit torque device. In this study, the possibility of control of the adjacent magnetic layer, CoFeB layer, was proved through the spin Nernst effect. In addition, by incorporating these results into the current induced spin orbit torque switching, the possibility of application as a SOT device was proved. Third, we report gate voltage modulation of the SSE in W/CoFeB/AlO$_x$/ZrO$_2$ structure. In this study, we succeeded in directly controlling this thermal spin current by applying a gate voltage. These results will open the possibility of utilizing spin thermoelectric phenomenon through thermal spin injection. The control of this spin thermoelectric phenomenon is meaningful in controls the entanglement of thermal and magnetic properties through gate voltage, not only in terms of application.