Spin Seebeck effect of solution processed ferrimagnet insulator thin film, Yttrium Iron Garnet

Abstract

Spin Seebeck effect, in combination with the Inverse Spin Hall Effect, can be applied directly for the conversion from heat to electric energy. Spin Seebeck thermoelectric generator allows new approaches toward the improvement of thermoelectric generation efficiency. In general, the conventional thermoelectric generator has the limitation of the efficiency due to the trade-off relation among Seebeck coefficient (S), electrical conductivity (σ), and thermal conductivity (k). In contrast, the application of ferrimagnet insulator in Spin Seebeck effect has great advantages for enhancing thermoelectric efficiency. In particularly, the input heat flux and generated charge currents flow in a perpendicular direction to each other so that it allows us to construct thermoelectric devices operating in more effective configuration. Conventionally, Yttrium Iron Garnet (YIG) has been most widely used as a ferrimagnet insulator to extract the heat induced spin current. Until now, pulsed laser deposition and liquid phase epitaxy grown films on Gd3Ga5O12 substrate have been used for the study of Spin Seebeck effect. Here, we deposited the solution processed poly-crystalline YIG thin films by using spin coating and annealing methods. The roughness of film can be easily controlled down to ~0.2 nm (5um by 5um). We observed the large signals of Spin Seebeck effect and Inverse Spin Hall effect inducing voltage in the solution processed poly-crystalline YIG/Pt hetero-structure. The estimated longitudinal spin seebeck coefficient is ~ 70nV/K. Our experiments can provide the breakthrough of the large area and easy process fabrication of YIG thin films for the efficient energy conversion from heat induced spin currents into the charge currents.