  We report on a systematic investigation of the longitudinal spin Seebeck
effect (LSSE) in a GGG(Gd3Ga5O12)/GdIG(Gd3Fe5O12)/Pt film series exhibiting an
in-plane magnetic easy axis with a compensation temperature (T_Comp) that
decreases from 270 to 220 K when decreasing GdIG film thickness from 272 to 31
nm, respectively. For all the films, the LSSE signal flips its sign below
T_Comp. We demonstrate a universal scaling behavior of the temperature
dependence of LSSE signal for our GdIG films around their respective T_Comp.
Additionally, we demonstrate LSSE in a 31 nm GdIG film grown on a
lattice-mismatched GSGG (Gd3Sc2Ga3O12) substrate that exhibits an out-of-plane
magnetic easy axis at room temperature. However, this sample reveals a spin
reorientation transition where the magnetic easy axis changes its orientation
to in-plane at low temperatures. We observed a clear distinction in the LSSE
signal for the GSGG/GdIG(31 nm)/Pt heterostructure, relative to
GGG/GdIG(31nm)/Pt showing an in-plane magnetic easy axis. Our findings
underscore a strong correlation between the LSSE signal and the orientation of
magnetic easy axis in compensated ferrimagnets and opens the possibility to
tune LSSE through effective anisotropy.
