Abstract
The rapidly growing fields of spin caloritonics and magnon spintronics have brought on a surge of interest in magnetic and thermal transport properties of magnetic insulators. Here we present low-temperature measurements of thermal conductivity and spin Seebeck effect in the helimagnetic insulator Cu2OSeO3 as functions of temperature, magnetic field, and crystallographic orientation. This compound hosts novel spin phases with long-period spin modulations, and its magnon thermal conductivity (~70 W/mK near 5 K) is the largest of any known ferro- or ferrimagnetic insulator. The magnetic field dependencies of thermal conductivity and spin Seebeck effect reveal novel aspects of phonon and magnon transport in chiral spin phases, like anisotropic scattering and domain structure. Analysis of the temperature dependence of spin Seebeck effect provides insight into the relevant time and length scales involved in thermally driven spin current phenomena.