  We study the transport of thermally excited non-equilibrium magnons through
the ferrimagnetic insulator YIG using two electrically isolated Pt strips as
injector and detector. The diffusing magnons induce a non- local inverse spin
Hall voltage in the detector corresponding to the so-called non-local spin
Seebeck effect (SSE). We measure the non-local SSE as a function of temperature
and strip separation. In experiments at room temperature we observe a sign
change of the non-local SSE voltage at a characteristic strip separation d0, in
agreement with previous investigations. At lower temperatures however, we find
a strong temperature dependence of d0. This suggests that both the angular
momentum transfer across the YIG/Pt interface as well as the transport
mechanism of the magnons in YIG as a function of temperature must be taken into
account to describe the non-local spin Seebeck effect.
