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

TLDR

A non‑local spin‑Seebeck measurement with a focused laser on bulk YIG and a Pt inverse spin Hall detector, combined with thermal modeling, establishes that thermally excited magnons diffuse laterally without spurious temperature gradients. The measured magnon spin diffusion length exceeds 120 µm at 23 K (47–73 µm) and falls below 10 µm at room temperature, suggesting that insulating spin conductors can power thermally driven spintronic devices.

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.