Phonon anomaly in the nonlocal spin Seebeck effect

The nonlocal spin Seebeck effect is an effective method to clarify the transport properties of thermally excited magnonic spin-current in Y₃Fe₅O₁₂ (YIG) [1]. Generation of magnonic spin-currents is affected by phonons due to the magneto-elastic coupling in YIG [2]. However, the effect of the magneto-elastic coupling on the magnon transport is yet to be elucidated. In this study, we clarified the role of phonons in the spin-current transport by measuring the magnetic field H dependence of nlSSE.
The sample comprises of two Pt wires patterned on a YIG substrate. When the current is applied to the one Pt wire, the Joule heat excites magnons in the YIG. The excited magnons propagate in the YIG and generate a voltage across the other Pt wire by the inverse spin Hall effect.
In the H dependence of nlSSE voltage V_nlSSE, a clear dip-like structure appears, which is caused by the hybridized magnon-phonon excitation, magnon-polarons. We explain the phonon anomaly in the nlSSE by the magnon chemical potential model including the effect of magnon-polaron formation [3].
[1] L. J. Cornelissen, et al., Nat. Phys. 11, 1022 (2015).; [2] T. Kikkawa, et al., Phys. Rev. Lett. 117, 207203 (2016).; [3] L. J. Cornelissen, K. Oyanagi, et al., Phys. Rev. B 96, 104441(2017).