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Thermoelectric spin voltage in graphene

Abstract

In recent years, new spin-dependent thermal effects have been discovered in ferromagnets, stimulating a growing interest in spin caloritronics, a field that exploits the interaction between spin and heat currents1,2. Amongst the most intriguing phenomena is the spin Seebeck effect3,4,5, in which a thermal gradient gives rise to spin currents that are detected through the inverse spin Hall effect6,7,8. Non-magnetic materials such as graphene are also relevant for spin caloritronics, thanks to efficient spin transport9,10,11, energy-dependent carrier mobility and unique density of states12,13. Here, we propose and demonstrate that a carrier thermal gradient in a graphene lateral spin valve can lead to a large increase of the spin voltage near to the graphene charge neutrality point. Such an increase results from a thermoelectric spin voltage, which is analogous to the voltage in a thermocouple and that can be enhanced by the presence of hot carriers generated by an applied current14,15,16,17. These results could prove crucial to drive graphene spintronic devices and, in particular, to sustain pure spin signals with thermal gradients and to tune the remote spin accumulation by varying the spin-injection bias.

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Fig. 1: Thermoelectric spin voltage.
Fig. 2: Device characteristics.
Fig. 3: Thermoelectric spin voltage detection.
Fig. 4: Modelling and roles of Seebeck coefficient and the spin accumulation.

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Acknowledgements

We thank D. Torres for help in designing Fig. 1. This research was partially supported by the European Research Council under grant agreement no. 306652 SPINBOUND, by the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 696656 (Graphene Flagship), by the Spanish Ministry of Economy and Competitiveness, MINECO (under contracts no. MAT2013-46785-P, no. MAT2016-75952-R and Severo Ochoa no. SEV-2013-0295), and by the CERCA Programme and the Secretariat for Universities and Research, Knowledge Department of the Generalitat de Catalunya 2014 SGR 56. J.F.S. and M.V.C. acknowledge support from MINECO Juan de la Cierva and Ramón y Cajal programmes, respectively, and J.C. from Generalitat de Catalunya, Beatriu de Pinos programme.

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J.F.S., I.N. and S.O.V. planned the measurements. J.F.S. fabricated the samples and performed the experiments. J.C., B.R. and M.V.C. provided support for the device fabrication and M.V.C. for the measurements. J.F.S. and S.O.V. analysed the data and wrote the manuscript. All authors discussed the results and commented on the manuscript. S.O.V supervised the work.

Corresponding authors

Correspondence to Juan F. Sierra or Sergio O. Valenzuela.

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The authors have no competing financial interests.

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Supplementary Text and Figures 1–4

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Sierra, J.F., Neumann, I., Cuppens, J. et al. Thermoelectric spin voltage in graphene. Nature Nanotech 13, 107–111 (2018). https://doi.org/10.1038/s41565-017-0015-9

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