Impact of Fe film thickness and Si(B) substrate on spin current and shunting effects in longitudinal spin Seebeck effect studies

This work investigates the longitudinal spin Seebeck effect (LSSE) in ferromagnetic Fe/Pt bilayer systems, examining the role of Fe layer thickness and substrate type on spin current dynamics and signal characteristics. Thin Fe films (3-20 nm) were sputtered onto Si/SiO2 and Si(B) substrates and analyzed for their structural, magnetic, and spin transport behaviors. The study identifies an optimal Fe thickness below 5 nm for effective spin injection, corresponding to a spin diffusion length of 4.7 nm, a spin Hall angle of 0.094, and a spin injection coefficient of −1.6 V (K·Ω·m)-1. Beyond 15 nm, the LSSE signal reverses due to dominant shunting effects. Substrate interactions significantly affect spin scattering, particularly at the Fe/Si(B) interface, where an insulating layer is necessary to stabilize magnetic and spin properties. These results provide insights into optimizing ferromagnetic metal-based LSSE systems for advanced spintronic applications. © 2025 The Author(s). Published by IOP Publishing Ltd.