Efficient spin transport in a paramagnetic insulator

Abstract

The discovery of new materials that efficiently transmit spin currents has been important for spintronics and material science. The electric insulator ${\mathrm{Gd}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ (GGG) is a superior substrate for growing magnetic films, but has never been considered as a conduit for spin currents. Here we report spin current propagation in paramagnetic GGG over several microns. Surprisingly, the spin transport persists up to temperatures of 100 K $\gg$ $T_{\mathrm{g}}=180$ mK, GGG's magnetic glass-like transition temperature. At 5 K we find a spin diffusion length ${\lambda }_{\mathrm{GGG}}=1.8\pm 0.2\mu$m and a spin conductivity ${\sigma }_{\mathrm{GGG}}=(7.3\pm 0.3)\times 10^4$ ${\mathrm{Sm}}^{-1}$ that is larger than that of the record quality magnet ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (YIG). We conclude that exchange coupling is not required for efficient spin transport, which challenges conventional models and provides new material-design strategies for spintronic devices.

21 pages, 4 figures