Spin-wave-induced lateral temperature gradient in a YIG thin film/GGG system excited in an ESR cavity

TL;DR

This study demonstrates that Damon-Eshbach mode-induced thermal gradients in YIG films occur even in ESR cavity excitation, revealing a surface damping imbalance that impacts spin-charge conversion measurements.

Contribution

It shows the existence of spin-wave-induced thermal gradients in YIG under ESR cavity excitation and links this to surface damping asymmetry, confirmed by micromagnetic simulations.

Findings

Thermal gradient peaks at 13 mK under 4 mW microwave power.

Damon-Eshbach mode causes surface imbalance in spin-wave populations.

Micromagnetic simulations support the damping asymmetry hypothesis.

Abstract

Lateral thermal gradient of an yttrium iron garnet (YIG) film under the microwave application in the cavity of the electron spin resonance system (ESR) was measured at room temperature by fabricating a Cu/Sb thermocouple onto it. To date, thermal transport in YIG films caused by the Damon-Eshbach mode (DEM) - the unidirectional spin-wave heat conveyer effect - was demonstrated only by the excitation using coplanar waveguides. Here we show that effect exists even under YIG excitation using the ESR cavity - tool often employed to realize spin pumping. The temperature difference observed around the ferromagnetic resonance (FMR) field under the 4 mW microwave power peaked at 13 mK. The observed thermoelectric signal indicates the imbalance of the population between the DEMs that propagate near the top and bottom surfaces of the YIG film. We attribute the DEM population imbalance to the different magnetic damping near the top and bottom YIG surfaces. Additionally, the spin wave dynamics of the system were investigated using the micromagnetic simulations. The micromagnetic simulations confirmed the existence of the DEM imbalance in the system with the increased Gilbert damping at one of the YIG interfaces. The reported results are indispensable for the quantitative estimation of the electromotive force in the spin-charge conversion experiments using ESR cavities.