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 Lu2Bi1Fe4Ga1O12 (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.

Long-distance transport of spin information in insulators without long-range magnetic order has been recently reported. Here, we perform a complete characterization of amorphous Y3Fe5O12 (a-YIG) films grown on top of SiO2. We confirm a clear amorphous structure and paramagnetic behavior of our a-YIG films, with semiconducting behavior resistivity that strongly decays with increasing temperature. The non-local transport measurements show a signal which is not compatible with spin transport and can be attributed to the drop of the a-YIG resistivity caused by Joule heating. Our results emphasize that exploring spin transport in amorphous materials requires careful procedures in order to exclude the charge contribution from the spin transport signals.Insulator-based spintronics is attracting a great amount of attention for the storage and transport of spin information because of the long spin propagation lengths [1] and the absence of energy dissipation due to ohmic losses [2] when compared to the conventional metal-based spintronics. In a ferri-and antiferromagnetic insulator, spin waves or magnons can carry spin information [1,2,[11][12][13][14][15][3][4][5][6][7][8][9][10]. In particular, yttrium iron garnet (Y3Fe5O12, YIG) is a ferrimagnetic insulator which has been broadly studied because of its small damping constant [16] and magnon propagation up to tens of microns [4] or even few millimeters [1,3].Up to now, long distance spin transport has been achieved in high-quality single-crystal magnetic insulators [1,2,[11][12][13][14][15]17,18,[3][4][5][6][7][8][9][10]. Moreover, recent reports have stimulated insulator-based spintronics by expanding the field to amorphous materials without long-range magnetic order [19,20]. Amorphous materials are promising for future spintronic devices due to the ease for mass production, small magnetic anisotropy, and less influence of the phonons because of the lack of crystal structure. The work of D. Wesenberg et. al. highlights the advantage of amorphous materials for long-range transport of spin information through an amorphous paramagnetic Y3Fe5O12 without any external magnetic field applied [19]. However, in contrast to single crystals,