Abnormal spin Seebeck effect near compensation temperature in Tb3Fe5O12 garnet films

We report the abnormal spin Seebeck effect (SSE) observed in Tb3Fe5O12(TbIG)/Pt heterostructures near the compensation temperature (Tcomp) of TbIG. As the temperature approaches Tcomp from room temperature, a rapid decline is shown in the spin Seebeck coefficient (SSC) from zero magnetic field to a high-field region, accompanied by its sign change. When the temperature decreases further below Tcomp, magnon-polaron anomalies appear in the SSC near zero field. These temperature-sensitive abnormal SSE behaviors are supported by theoretical calculations, revealing the rotation of the net magnetic moment of Fe sublattices above Tcomp and the magnon-polaron formation due to the hybridization of magnon and longitudinal acoustic phonon below Tcomp. The observed abnormal SSE is related to the highly tunable noncollinear magnetic spin texture and its magnon dispersion. This work highlights the impact of diverse sublattice-dominated magnons on SSE, paving a new avenue for exploring the magnon spintronic devices in rare-earth iron garnets.