Bruce William Alphenaar

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, 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.

Spin electronics using carbon nanotubes

Abstract We use ferromagnetic contacts to inject and detect spin-polarized electrons in multi-walled carbon nanotubes. The small diameter of the nanotube allows us to probe individual magnetic domains. As the alignment of the magnetizations within a pair of contacts switches from parallel to antiparallel, the nanotube resistance switches from a low to a high resistance state. This result is a first step towards the possibility of carbon nanotube-based spin electronics.

Magnetoresistance of ferromagnetically contacted carbon nanotubes

Abstract Magnetoresistance measurements of multi-walled carbon nanotubes having one or two ferromagnetic contacts are compared. Nanotubes with two cobalt contacts show hysteretic switching in the magnetoresistance, with a maximum change of 9% at 4.2 K , while nanotubes with one cobalt contact and one platinum/gold contact show no magnetoresistance switching. This provides further evidence for coherent transport of electron spin through the multi-walled nanotube. In addition, the magnetoresistance ratio in the ferromagnetic nanotube device is calculated for a two-band ballistic model, and gives a maximum value of 25%.