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Coherent transport of electron spin in a ferromagnetically contacted carbon nanotube

Abstract

Conventional electronic devices generally utilize only the charge of conduction electrons; however, interest is growing in ‘spin-electronic’ devices1, whose operation depends additionally on the electronic spin. Spin-polarized electrons (which occur naturally in ferromagnetic materials) can be injected from a ferromagnet into non-ferromagnetic materials2,3,4, or through oxide tunnel barriers3,5,6,7,8,9,10. The electron-scattering rate at any subsequent ferromagnetic/non-ferromagnetic interface depends on the spin polarity, a property that is exploited in spin-electronic devices. The unusual conducting properties11,12,13,14,15,16,17,18 of carbon nanotubes offer intriguing possibilities for such devices; their elastic- and phase-scattering lengths are extremely long16,17, and carbon nanotubes can behave as one-dimensional conductors18. Here we report the injection of spin-polarized electrons from ferromagnetic contacts into multi-walled carbon nanotubes, finding direct evidence for coherent transport of electron spins. We observe a hysteretic magnetoresistance in several nanotubes with a maximum resistance change of 9%, from which we estimate the spin-flip scattering length to be at least 130 nm—an encouraging result for the development of practical nanotube spin-electronic devices.

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Figure 1: Structure of our devices, consisting of a single multi-walled carbon nanotube (MWNT) electrically contacted by ferromagnetic Co.
Figure 2: Two-terminal differential resistance as a function of magnetic field for three different MWNT devices.
Figure 3: Detailed characterization of a single nanotube device.

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Acknowledgements

We thank H. Mizuta, T. Nakanishi, M. D. R. Thomas, D. G. Hasko and H. O. Müller for discussions.

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Correspondence to Bruce W. Alphenaar.

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Tsukagoshi, K., Alphenaar, B. & Ago, H. Coherent transport of electron spin in a ferromagnetically contacted carbon nanotube. Nature 401, 572–574 (1999). https://doi.org/10.1038/44108

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