Credit: © 2007 AIP

Graphene sheets comprise carbon atoms bonded together in a flat hexagonal array, which constitute graphite when stacked together in layers. The physical stability, robustness and large mean free path of charge carriers in these two-dimensional sheets make graphene a promising material for a wide range of applications in the field of nanoelectronics.

In particular, the ability to control the spin of electrons flowing through graphene layers would enable this material to be used in the fabrication of so-called 'spintronic' devices. Now, Alan Goldman and Masaya Nishioka at the University of Minnesota, Minneapolis in the USA report on the magnetoresistance characteristics of a spin valve device with a cobalt/multilayer-graphene/cobalt structure1. The graphene multilayer (containing six carbon layers) was produced by cleaving graphite, and then a thin film (20-nm-thick) of ferromagnetic cobalt was deposited on top using electron-beam evaporation to produce two contacts.

Application of a magnetic field in the 'easy' direction of the Co film produced a maximum (0.39%) change in resistance at a temperature of 2 K, with the change being dependent on the magnitude of the excitation current and measurement temperature. These results are attributed to magnetoresistance spin-dominated transport through the six-layer graphene structure. The ability to both modulate the conductivity of graphene sheets and manipulate spin current opens up the possibility of using graphene for spintronic devices.