Heat Transport by Spin Waves in Yttrium Iron Garnet

Abstract

The thermal conductivity of two single-crystal samples of the ferrimagnet yttrium iron garnet is reported between 0.4 and 20°K from 0 to 20 kOe. A 70% decrease in conductivity occurs when a strong magnetic field is applied at 0.5°K, and smaller reductions at higher temperatures. The results are interpreted as evidence for heat transport by spin waves, which has never been observed in other materials. The two samples show somewhat different temperature, field-magnitude, and field-direction dependences. These differences are qualitatively discussed, and can reasonably be ascribed to impurities.