  This article reports temperature-dependent measurements of longitudinal spin
Seebeck effects (LSSEs) in Pt/Y$_3$Fe$_5$O$_{12}$ (YIG)/Pt systems in a high
temperature range from room temperature to above the Curie temperature of YIG.
The experimental results show that the magnitude of the LSSE voltage in the
Pt/YIG/Pt systems rapidly decreases with increasing the temperature and
disappears above the Curie temperature. The critical exponent of the LSSE
voltage in the Pt/YIG/Pt systems at the Curie temperature was estimated to be
3, which is much greater than that for the magnetization curve of YIG. This
difference highlights the fact that the mechanism of the LSSE cannot be
explained in terms of simple static magnetic properties in YIG.
