Flexible spin-caloritronic devices

Abstract

Flexible thermoelectric generator (TEG) [1] is a fast-evolving research field in a future sustainable energy technology as well as an internet of things (IoT). One of the prominent candidates for a flexible TEG is a spin Seebeck effect (SSE) device [2] which has a device-design flexibility and scaling capability [3]. Here we proposed a novel method for fabricating substrate-free flexible YIG sheet through the sol-gel synthesis which enables low-cost mass production. Through the optimization of the heat treatments and adding newly-developed mechanical process in a conventional sol-gel synthesis process, we obtained considerable enhancement of the saturation magnetization and the thermoelectric efficiency of flexible YIG sheet compare to them of a polycrystalline YIG sheet [4]. For converting spin to charge current through the inverse spin Hall effect, a gold (Au) electrode was sputtered on the surface of three different YIG sheets. To magnetize YIG sheet along the film surface direction, 400-Oe magnetic field was applied. Temperature gradient was applied perpendicular to the magnetization direction of an YIG sheet and parallel to the flow of spin currents, which is well-known the longitudinal configuration of SSE. In this study, for temperature difference (ΔT) of 40 K, our flexible SSE devices reliably generated thermoelectric voltages as shown in Fig. 1(b). Flexible substrate-free SSE device fabricated by the sol-gel synthesis will pave the way for harnessing spin caloritronic to energy harvesting devices for next-generation smart network devices which related to IoT.