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 the 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 method and we evaluated their structural and LSSE properties. The fabricated [YIG/Pt]\(_n\) samples show flat YIG/Pt interfaces and almost identical saturation magnetization \(M_{\rm s}\), 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 \(\sim 28\) compared to that of [YIG/Pt]\(_1\). This work may provide a guideline for developing future multilayerbased LSSE devices.