Dr. Takashi Kikkawa
Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Japan
Date & Time: 15:00 - 16:00, Dec. 19th (Fri), 2025.
Place: 8F Conference Room, Main Bldg., Sengen.
(The 295th Special CMSM seminar)
Observation of nonlinear Seebeck effect
Dr. Takashi Kikkawa
Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Japan
Abstract:
Thermoelectric effects convert heat into electricity and have long underpinned environmentally friendly power generation and sensing technologies. However, conventional thermoelectric phenomena—including the Seebeck and Nernst effects—have been confined to the linear regime with respect to the applied temperature gradient ∇T. In this regime, the net thermoelectric voltage V vanishes in the absence of a macroscopic ∇T (i.e., V = 0 for 〈∇T〉 = 0), because the voltage reverses sign when the ∇T direction is reversed, V(+∇T) = –V(–∇T), limiting their application in realistic environments.
In this talk, I will introduce the emerging concept of nonlinear thermoelectricity [1,2], in which the output voltage scales with the temperature-gradient squared (∇T)2, allowing thermoelectric generation even without a macroscopic ∇T. I will first give a brief overview of the observation of a nonlinear Nernst effect in a superconducting MoGe film on the ferrimagnetic insulator Y3Fe5O12 and present the experimental method for measuring nonlinear thermoelectric effects using a lock-in technique [1]. I will then move on to our recent demonstration of the nonlinear Seebeck effect in NiFe|Pt bilayers at room temperature [2]. The observed nonlinear Seebeck voltage scales with (∇T)2 and is interpreted as the thermoelectric counterpart of the unidirectional spin Hall magnetoresistance found in spintronics. The nonlinear Seebeck voltage increases as the sample length along the ∇T direction decreases, showing a characteristic scaling law distinct from the conventional linear Seebeck effect.
References
[1] H. Arisawa, Y. Fujimoto, T. Kikkawa, and E. Saitoh*, Observation of nonlinear thermoelectric effect in MoGe/Y3Fe5O12, Nat. Commun. 15, 6912 (2024).
[2] Y. Hirata*, T. Kikkawa*, H. Arisawa, and E. Saitoh, Nonlinear Seebeck effect in Ni81Fe19|Pt at room temperature, Appl. Phys. Lett. 126, 252408 (2025).
In this talk, I will introduce the emerging concept of nonlinear thermoelectricity [1,2], in which the output voltage scales with the temperature-gradient squared (∇T)2, allowing thermoelectric generation even without a macroscopic ∇T. I will first give a brief overview of the observation of a nonlinear Nernst effect in a superconducting MoGe film on the ferrimagnetic insulator Y3Fe5O12 and present the experimental method for measuring nonlinear thermoelectric effects using a lock-in technique [1]. I will then move on to our recent demonstration of the nonlinear Seebeck effect in NiFe|Pt bilayers at room temperature [2]. The observed nonlinear Seebeck voltage scales with (∇T)2 and is interpreted as the thermoelectric counterpart of the unidirectional spin Hall magnetoresistance found in spintronics. The nonlinear Seebeck voltage increases as the sample length along the ∇T direction decreases, showing a characteristic scaling law distinct from the conventional linear Seebeck effect.
References
[1] H. Arisawa, Y. Fujimoto, T. Kikkawa, and E. Saitoh*, Observation of nonlinear thermoelectric effect in MoGe/Y3Fe5O12, Nat. Commun. 15, 6912 (2024).
[2] Y. Hirata*, T. Kikkawa*, H. Arisawa, and E. Saitoh, Nonlinear Seebeck effect in Ni81Fe19|Pt at room temperature, Appl. Phys. Lett. 126, 252408 (2025).
(Contact)
Ken-ichi Uchida
Distinguished Group Leader, Spin Caloritronics Group
E-mail: UCHIDA.Kenichi[at]nims.go.jp
Distinguished Group Leader, Spin Caloritronics Group
E-mail: UCHIDA.Kenichi[at]nims.go.jp