Magnetic field dependence of the nonlocal spin Seebeck effect in Pt/YIG/Pt systems at low temperatures

We report the nonlocal spin Seebeck effect (nlSSE) in a lateral configuration of Pt/Y3Fe5O12(YIG)/Pt systems as a function of the magnetic field B (up to 10 T) at various temperatures T (3 K < T < 300 K). The nlSSE voltage decreases with increasing B in a linear regime with respect to the input power (the applied charge-current squared I2). The reduction of the nlSSE becomes substantial when the Zeeman energy exceeds thermal energy at low temperatures, which can be interpreted as freeze-out of magnons relevant for the nlSSE. Furthermore, we found the nonlinear power dependence of the nlSSE with increasing I at low temperatures (T < 20 K), at which the B-induced signal reduction became less visible. Our experimental results suggest that in the nonlinear regime, high-energy magnons are overpopulated compared to those expected from the thermal energy. We also estimate the magnon spin diffusion length as functions of B and T.