Spin transport in insulators without exchange stiffness

Authors
Koichi Oyanagi, Saburo Takahashi, Ludo J. Cornelissen, Juan Shan, Shunsuke Daimon, Takashi Kikkawa, Gerrit E. W. Bauer, Bart J. van Wees, and Eiji Saitoh

Abstract
The discovery of new materials that efficiently transmit spin currents has been important for spintronics and material science. The electric insulator Gd₃Ga₅O₁₂ (GGG), a standard substrate for growing magnetic films, can be a spin current generator, but has never been considered as a superior conduit for spin currents. Here we report spin current propagation in paramagnetic GGG over several microns. Surprisingly, spin transport persists up to temperatures of 100 K ≫">≫≫ T_g = 180 mK, the magnetic glass-like transition temperature of GGG. At 5 K and 3.5 T, we find a spin diffusion length λ_GGG = 1.8 ± 0.2 μm and a spin conductivity σ_GGG = (7.3 ± 0.3) × 10⁴ Sm⁻¹ that is larger than that of the record quality magnet Y₃Fe₅O₁₂ (YIG). We conclude that exchange stiffness is not required for efficient spin transport, which challenges conventional models and provides new material-design strategies for spintronic devices.

Nature Communications：https://www.nature.com/articles/s41467-019-12749-7