  We report the observation of anomalous peak structures induced by hybridized
magnon-phonon excitation (magnon polarons) in the magnetic field dependence of
the spin Peltier effect (SPE) in a Lu$_{2}$Bi$_{1}$Fe$_{4}$Ga$_{1}$O$_{12}$
(BiGa:LuIG) with Pt contact. The SPE peaks coincide with magnetic fields tuned
to the threshold of magnon-polaron formation, consistent with the previous
observation in the spin Seebeck effect. The enhancement of SPE is attributed to
the lifetime increase in spin current caused by magnon-phonon hybridization in
BiGa:LuIG.
