1. Department of Applied Physics and Physico-Informatics, Keio University, Yokohama 223-8522, Japan
2. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
3. CREST, Japan Science and Technology Agency, Sanbancho, Tokyo 102-0075, Japan
4. Cross-Correlated Materials Research Group, RIKEN, Wako, Saitama 351-0198, Japan
5. PRESTO, Japan Science and Technology Agency, Sanbancho, Tokyo 102-0075, Japan

Correspondence to: E. Saitoh^1,5 Correspondence and requests for materials should be addressed to E.S. (Email: saitoheiji@appi.keio.ac.jp).

Abstract

The generation of electric voltage by placing a conductor in a temperature gradient is called the Seebeck effect^{1, 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 thermocouple^{1, 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 effect^{3, 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 spintronic^{15, 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.

1. Department of Applied Physics and Physico-Informatics, Keio University, Yokohama 223-8522, Japan
2. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
3. CREST, Japan Science and Technology Agency, Sanbancho, Tokyo 102-0075, Japan
4. Cross-Correlated Materials Research Group, RIKEN, Wako, Saitama 351-0198, Japan
5. PRESTO, Japan Science and Technology Agency, Sanbancho, Tokyo 102-0075, Japan

Correspondence to: E. Saitoh^1,5 Correspondence and requests for materials should be addressed to E.S. (Email: saitoheiji@appi.keio.ac.jp).

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