  Our joint theoretical and computer experimental study of heat-to-spin
conversion reveals that noncollinear antiferromagnetic insulators are promising
materials for generating magnon spin currents upon application of a temperature
gradient: they exhibit spin Seebeck and spin Nernst effects. Using Kubo theory
and spin dynamics simulations, we explicitly evaluate these effects in a single
kagome sheet of potassium iron jarosite, KFe$_3$(OH)$_6$(SO$_4$)$_2$, and
predict a spin Seebeck conversion factor of $0.2 \mu\mathrm{V}/\mathrm{K}$ at a
temperature of $20 \mathrm{K}$.
