  The spin Peltier effect (SPE), heat-current generation due to spin-current
injection, in various metal (Pt, W, and Au single layers and Pt/Cu
bilayer)/ferrimagnetic insulator (yttrium iron garnet: YIG) junction systems
has been investigated by means of a lock-in thermography (LIT) method. The SPE
is excited by a spin current across the metal/YIG interface, which is generated
by applying a charge current to the metallic layer via the spin Hall effect.
The LIT method enables the thermal imaging of the SPE free from the
Joule-heating contribution. Importantly, we observed spin-current-induced
temperature modulation not only in the Pt/YIG and W/YIG systems but also in the
Au/YIG and Pt/Cu/YIG systems, excluding the possible contamination by anomalous
Ettingshausen effects due to proximity-induced ferromagnetism near the
metal/YIG interface. As demonstrated in our previous study, the SPE signals are
confined only in the vicinity of the metal/YIG interface; we buttress this
conclusion by reducing a spatial blur due to thermal diffusion in an infrared
emission layer on the sample surface used for the LIT measurements. We also
found that the YIG-thickness dependence of the SPE is similar to that of the
spin Seebeck effect measured in the same Pt/YIG sample, implying the reciprocal
relation between them.
