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Observation of the spin Seebeck effect

Abstract

The generation of electric voltage by placing a conductor in a temperature gradient is called the Seebeck effect1,2. Its efficiency is represented by the Seebeck coefficient, S, which is defined as the ratio of the generated electric voltage to the temperature difference, and is determined by the scattering rate and the density of the conduction electrons. The effect can be exploited, for example, in thermal electric-power generators and for temperature sensing, by connecting two conductors with different Seebeck coefficients, a device called a thermocouple1,2. Here we report the observation of the thermal generation of driving power, or voltage, for electron spin: the spin Seebeck effect. Using a recently developed spin-detection technique that involves the spin Hall effect3,4,5,6,7,8,9,10,11,12,13,14, we measure the spin voltage generated from a temperature gradient in a metallic magnet. This thermally induced spin voltage persists even at distances far from the sample ends, and spins can be extracted from every position on the magnet simply by attaching a metal. The spin Seebeck effect observed here is directly applicable to the production of spin-voltage generators, which are crucial for driving spintronic15,16,17,18 devices. The spin Seebeck effect allows us to pass a pure spin current19, a flow of electron spins without electric currents, over a long distance. These innovative capabilities will invigorate spintronics research.

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Figure 1: The spin Seebeck effect.
Figure 2: Experimental set-up.
Figure 3: Measurements of electromotive force.
Figure 4: Dependence on magnetic field angle and position of Pt wire.

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Acknowledgements

The authors thank Y. Suzuki, S. E. Barnes, Y. Fujitani, G. Tatara, K. M. Itoh, H. Kuwahara and M. Matoba for discussions. This work was supported by a Grant-in-Aid for Scientific Research in Priority Area ‘Creation and control of spin current’ (19048028) from MEXT, Japan, a Grant-in-Aid for Encouragement of Young Scientists (A) from MEXT, Japan, the global COE for the ‘High-level global cooperation for leading-edge platform on access spaces’ from MEXT, Japan, a Strategic Information and Communications R&D Promotion Programme from MIC, Japan, and the Next Generation Supercomputing Project of Nanoscience Program from IMS, Japan.

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Uchida, K., Takahashi, S., Harii, K. et al. Observation of the spin Seebeck effect. Nature 455, 778–781 (2008). https://doi.org/10.1038/nature07321

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