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Thermal spin current from a ferromagnet to silicon by Seebeck spin tunnelling

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Abstract

Heat generation by electric current, which is ubiquitous in electronic devices and circuits, raises energy consumption and will become increasingly problematic in future generations of high-density electronics. The control and re-use of heat are therefore important topics for existing and emerging technologies, including spintronics. Recently it was reported that heat flow within a ferromagnet can produce a flow of spin angular momentum—a spin current—and an associated voltage1. This spin Seebeck effect has been observed in metallic1,2, insulating3 and semiconductor ferromagnets4 with temperature gradients across them. Here we describe and report the demonstration of Seebeck spin tunnelling—a distinctly different thermal spin flow, of purely interfacial nature—generated in a tunnel contact between electrodes of different temperatures when at least one of the electrodes is a ferromagnet. The Seebeck spin current is governed by the energy derivative of the tunnel spin polarization. By exploiting this in ferromagnet–oxide–silicon tunnel junctions, we observe thermal transfer of spins from the ferromagnet to the silicon without a net tunnel charge current. The induced spin accumulation scales linearly with heating power and changes sign when the temperature differential is reversed. This thermal spin current can be used by itself, or in combination with electrical spin injection, to increase device efficiency. The results highlight the engineering of heat transport in spintronic devices and facilitate the functional use of heat.

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Figure 1: Basic concept of Seebeck spin tunnelling.
Figure 2: Observation of thermal spin current from ferromagnet to silicon by Seebeck spin tunnelling.
Figure 3: Origin of Seebeck spin tunnelling and model calculation of salient characteristics.
Figure 4: Sign reversal of thermal spin current by heating the silicon or the ferromagnet.

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Acknowledgements

We are grateful to S. P. Dash for help with the device fabrication and discussions, T. Yorozu for the finite-element calculations and A. Yamamoto for making the finite-element program available to us. This work was financially supported by the program “Controlling spin dynamics in magnetic nanostructures” of the Netherlands Foundation for Fundamental Research on Matter (FOM).

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Contributions

J.-C.L.B. and R.J. designed the experiments. J.-C.L.B. and S.S. fabricated the devices. J.-C.L.B., S.S., H.S. and R.J. contributed to the measurements. R.J. developed the model calculation. All authors contributed to the planning, discussion and analysis of the research, and to the writing of the manuscript.

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Correspondence to Ron Jansen.

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The authors declare no competing financial interests.

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This file contains Supplementary Text and Data 1-7, Supplementary Figures 1-8 with legends, Supplementary Table 1 and additional references. (PDF 611 kb)

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Le Breton, JC., Sharma, S., Saito, H. et al. Thermal spin current from a ferromagnet to silicon by Seebeck spin tunnelling. Nature 475, 82–85 (2011). https://doi.org/10.1038/nature10224

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