Coherent transport of electron spin in a ferromagnetically contacted carbon nanotube

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(2-4), or through oxide tunnel barriers(3,5-10) 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 properties(11-18) of carbon nanotubes offer intriguing possibilities for such devices; their elastic- and phase-scattering lengths are extremely long(16,17), and carbon nanotubes can behave as one-dimensional conductors(18). 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.