Fabrication of yttrium–iron–garnet/Pt multilayers for the longitudinal spin Seebeck effect

For longitudinal spin Seebeck effect (LSSE) devices, a multilayer structure comprising ferromagnetic and nonmagnetic layers is expected to improve their thermoelectric power. In this study, we developed a fabrication method for alternately stacked yttrium–iron–garnet (YIG)/Pt multilayer films on a gadolinium gallium garnet (GGG) (110) substrate, GGG/[YIG(49 nm)/Pt(4 nm)]n n = 1–5 based on room-temperature sputtering and ex-situ post-annealing methods and we evaluated their structural and LSSE properties. The fabricated [YIG/Pt]n samples show flat YIG/Pt interfaces and almost identical saturation magnetization Ms although they contain polycrystalline YIG layers on Pt layers as well as single-crystalline YIG layers on GGG. In the samples, we observed clear LSSE signals and found that the LSSE thermoelectric power factor (PF) increases monotonically with increasing n; the PF of the [YIG/Pt]5 sample is enhanced by a factor of ∼28 compared to that of [YIG/Pt]1. This work may provide a guideline for developing future multilayer-based LSSE devices.