Graphene Nanoribbon Spin-Valve Device
Spin-valve devices are a key component of a magnetoresistive random access memory. Mr. Woo Youn Kim and Professor Kwang Soo Kim of Department of Chemistry of POSTECH predicted supermagnetoresistance in a graphene nanoribbon device, the article of which has appeared in Nature Nanotech (3, 408-412, 2008). The reported graphene nanoribbon spin-valve device shows extremely large magnetoresistance (ten thousand times larger than that of conventional devices), which promises high speed access, and good sensitivity. The striking enhancement originates from the peculiar symmetry of band structures of graphene nanoribbon in addition to the spin symmetry. The characteristic symmetry of the graphene band structure plays the role of a spin filter in perfectly transmitting the spin current in the case of symmetric band alignments between both ends of the nanoribbon and in completely forbidding the spin current in the case of orthogonal symmetric alignments. This phenomenon is highly contrasted to conventional spin-valves of giant magnetoresistance (GMR) or tunneling magnetoresistance (TMR) which utilizes only the spin symmetry and antisymmetry. The discovery of the GMR phenomenon was awarded the Nobel Prize in Physics last year. The present supermagnetoresistance ideally approaches to the infinite. Thus, the predicted new physics would open a new pathway much beyond the current limit of spin-valve devices.
Professor Kwang Soo Kim
Department of Chemistry