Long range pure magnon spin diffusion observed in a non-local spin-Seebeck geometry

TL;DR

This study measures the long-range diffusion of thermally excited magnon spins in yttrium iron garnet using a non-local spin-Seebeck setup, revealing diffusion lengths up to 73 micrometers at low temperatures.

Contribution

It provides the first direct measurement of long-range magnon spin diffusion in a non-local geometry, showing robustness against inelastic scattering at low temperatures.

Findings

Magnon spins travel over 120 μm at 23 K.

Spin diffusion length is at least 47 μm at 23 K.

Diffusion length drops below 10 μm at room temperature.

Abstract

The spin diffusion length for thermally excited magnon spins is measured by utilizing a non-local spin-Seebeck effect measurement. In a bulk single crystal of yttrium iron garnet (YIG) a focused laser thermally excites magnon spins. The spins diffuse laterally and are sampled using a Pt inverse spin Hall effect detector. Thermal transport modeling and temperature dependent measurements demonstrate the absence of spurious temperature gradients beneath the Pt detector and confirm the non-local nature of the experimental geometry. Remarkably, we find that thermally excited magnon spins in YIG travel over 120 $\mu$m at 23 K, indicating that they are robust against inelastic scattering. The spin diffusion length is found to be at least 47 $\mu$m and as high as 73 $\mu$m at 23 K in YIG, while at room temperature it drops to less than 10 $\mu$m. Based on this long spin diffusion length, we envision the development of thermally powered spintronic devices based on electrically insulating, but spin conducting materials.