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

TL;DR

This study presents a new fabrication method for YIG/Pt multilayers that enhances the longitudinal spin Seebeck effect, showing increased thermoelectric power with more layers, which could advance LSSE device development.

Contribution

Developed a room-temperature sputtering and post-annealing method to fabricate YIG/Pt multilayers with improved LSSE properties and demonstrated power factor enhancement with increasing layer number.

Findings

LSSE signals observed in all multilayer samples

Power factor increased monotonically with layer number

Maximum enhancement of ~28 times in the five-layer sample

Abstract

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.