Temperature dependence of the magnon spin diffusion length and magnon spin conductivity in the magnetic insulator yttrium iron garnet

TL;DR

This study investigates how the magnon spin diffusion length and conductivity in yttrium iron garnet vary with temperature, revealing a decrease in both parameters at lower temperatures and an unexpected enhancement of thermally generated magnon signals around 7 K.

Contribution

It provides the first systematic measurement of temperature-dependent magnon spin transport properties in yttrium iron garnet using non-local devices.

Findings

Magnon spin diffusion length decreases from 9.6 μm at room temperature to 5.5 μm at 30 K.

Magnon spin conductivity drops from 5.1×10^5 S/m at room temperature to 0.7×10^5 S/m at 5 K.

Thermally generated magnon signals are enhanced at low temperatures, peaking around 7 K.

Abstract

We present a systematic study of the temperature dependence of diffusive magnon spin transport, using a non-local device geometry. In our measurements, we detect spin signals arising from electrical and thermal magnon generation, and we directly extract the magnon spin diffusion length $\lambda_m$ for temperatures from 2 to 293 K. Values of $\lambda_m$ obtained from electrical and thermal generation agree within the experimental error, with $\lambda_m=9.6\pm0.9$ $\mu$m at room temperature to a minimum of $\lambda_m=5.5\pm0.7$ $\mu$m at 30 K. Using a 2D finite element model to fit the data obtained for electrical magnon generation we extract the magnon spin conductivity $\sigma_m$ as a function of temperature, which is reduced from $\sigma_m=5.1\pm0.2\times10^5$ S/m at room temperature to $\sigma_m=0.7\pm0.4\times10^5$ S/m at 5 K. Finally, we observe an enhancement of the signal originating from thermally generated magnons for low temperatures, where a maximum is observed around $T=7$ K. An explanation for this low temperature enhancement is however still missing and requires additional investigations.