conventional electronic devices generally utilize only the charge of conduction electrons; however, interest is growing in 'spin-electronic' devices, 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 materials, or through oxide tunnel barriers. 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 properties of carbon nanotubes offer intriguing possibilities for such devices; their elastic- and phase-scattering lengths are extremely long, and carbon nanotubes can behave as one-dimensional conductors. 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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