Nanoscale sensing applications require significant power to operate, which can be largely supplied through the efficient management of omnipresent heat. The spin Seebeck effect (SSE) is rather a fresh energy harvesting phenomenon that enables the conversion of a temperature gradient across magnetic materials into spin current. This spin current can further be converted into charge current by adjoining heavy metals to the magnet. In this study, we fabricated the thermoelectric multilayer films of bismuth-substituted neodymium iron garnet (Nd 2 Bi 1 Fe 5 O 12) (NIG) as well as gallium and bismuth co-substituted neodymium iron garnet (Nd 2 Bi 1 Fe 4 Ga 1 O 12) (NIGG) on (111)-oriented gallium gadolinium garnet substrates by metal organic decomposition. The thicknesses of the NIG and NIGG multilayers are varied to control the magnetic properties. The observed spin Seebeck signal is found to be directly dependent on the garnet/heavy metal interface and tends to decrease in intensity with increasing amount of NIGG in the garnet multilayers. Our results emphasize the importance of magnet/ heavy metal interface properties for designing SSE-based sensors.