Distinct Detection of Thermally Induced Spin Voltage in Pt/WS2/Ni81Fe19 by the Inverse Spin Hall Effect.

Abstract

Conversion of heat into a spin current by means of the spin Seebeck effect (SSE) is one of the exciting topics in spin caloritronics. By use of this technique, the excess heat may be transformed into a valuable electric voltage by coupling SSE with the inverse spin Hall effect (ISHE). In this study, a thermal gradient and an in-plane magnetic field are used as the driving power to mobilize the spin electrons to produce SSE. A spin voltage is detected by ISHE in the Ni81Fe19 heterostructure by means of a WS2/Pt strip. Using WS2 sheets of different thicknesses, we obtained a large spin Seebeck coefficient of 0.72 μV/K, which is 12 times greater than the conventional spin Seebeck coefficient observed in Pt/Ni81Fe19 bilayer devices. We observe the thickness dependence of tungsten disulfide (WS2) flakes and the polarity reversal of pure SSE signals that are measured without influence from the other thermoelectric effects in our Pt/WS2/Ni81Fe19 device-the most intriguing feature of this study. Without the electric charge conduction, the spins are distributed over a longer distance that is greater than the spin diffusion length of the Ni81Fe19 layer. Such features are strongly desired for designing the efficient spin-caloritronics devices that may be used in the thermoelectric spin generators and the temperature sensors such as thermocouples.