Nonlinear Seebeck effect in NiFe|Pt at room temperature

Hirata, Yuya*; Kikkawa, Takashi; Arisawa, Hiroki*; Saito, Eiji*

The nonlinear Seebeck effect, nonlinear conversion of a temperature gradient into an electric current, was observed at room temperature. Based on a second-harmonic lock-in method combined with an a.c. temperature gradient, , we measured a nonlinear Seebeck voltage in NiFe|Pt bilayers at 300 K, the amplitude of which increases in proportion to . We also observed that the nonlinear Seebeck voltage increases as the sample length along the direction decreases, showing a characteristic scaling law distinct from the conventional linear Seebeck effect. We developed a phenomenological model for the nonlinear Seebeck effect incorporating the spin-current induced modulation of the Seebeck coefficient, which well reproduces the experimental results.