A New Twist on Spintronics

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Science  18 Feb 2011:
Vol. 331, Issue 6019, pp. 864-865
DOI: 10.1126/science.1201663

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Great hopes exist for improving the storage and processing of information by using not only the charge of electrons, as is done in everyday electronics, but by also exploiting a quantum mechanical property of electrons known as spin. In the rapidly growing field of spintronics (1), the electron spin is essentially a minute magnet that can be pointing either “up” or “down.” The most efficient way to manipulate spins is by means of a magnetic field, either externally applied or existing inside a ferromagnetic material. By sending electrons through ferromagnetic materials, scientists have achieved spin-filtering effects, discriminating between electrons with “up” and “down” spins, with selectivity up to 25% (2). On page 894 of this issue, Göhler et al. (3) describe a surprisingly efficient method for electronic spin filtering. They have studied how electrons emitted by a gold substrate, upon absorption of light, pass through a self-assembled DNA monolayer on the gold surface. In particular, they have studied the spin of the electrons after their passage through the DNA layer and have found that one spin type passes through much more easily, meaning that this layer acts as a spin filter, strongly hindering the passage of the other spin type. This filter effect is observed only if the DNA is assembled on the gold surface as a closely packed ordered array of helices, and is stronger if the helices are longer, reaching selectivities of 60%. For chaotic assemblies of floppy DNA chains on the gold surface, the spin filter effect was not observed.