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

The spin diffusion length for thermally excited magnon spins is measured by utilizing a nonlocal 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 nonlocal 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.