|NEWS OF THE WEEK
Volume 80, Number 16
CENEAR 80 16 p. 7
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The realms of molecular electronics and spin-based electronics (spintronics) have been merged in a new device--a single-molecule spin valve.
The new variant on the spin valve is the first to involve a single organic molecule. A conventional spin valve in its most basic form is a thin layer of a nonmagnetic metal sandwiched between two ferromagnetic layers. In one of the ferromagnetic layers, the aligned electron spins have been "pinned" and cannot be easily changed. In the other, "free" magnetic layer, the orientation of the spins can be changed by applying a relatively small magnetic field.
When the spins in the two magnetic layers are aligned, a current of electrons with the same spin can pass through the sandwich easily. But when the spins in the magnetic layers are opposed, the electrical resistance of the device is higher, impeding the flow of current. Such a spin valve, built into a read head, can sense the magnetism of data bits on a computer hard drive.
In Schön's device, the magnetic layers are two nickel electrodes that sandwich a 1-nm-thick self-assembled monolayer [Science, published online April 18, http://www.sciencemag.org/cgi/content/abstract/1070563v1]. The monolayer is thought to have about one molecule of benzene-1,4-dithiolate, which can conduct electrons, in an insulating "carpet" of roughly 105 molecules of 1-pentanethiol. When the spins in both nickel electrodes point in the same direction, current flows through the dithiolate molecule. But when the electrodes' spin orientations are opposite, the resistivity of the device jumps by 30% at room temperature.
"This work is very interesting from the scientific standpoint since it shows that the electron spin direction is preserved when the spin-polarized electron current is transported through a single organic molecule," says Stuart A. Wolf, a program manager for spintronics at the Defense Advanced Research Projects Agency. "This portends very well for organic spintronics," which is perhaps 10 years away.
"When devices and circuits reach the nano scale (15 nm), spin will be the preferred method for storing and transporting information in the solid state," Wolf believes. "Thus, although this device relies on metallic ferromagnetic contacts, it means that when we develop molecular ferromagnets at room temperature, we will have most of the building blocks for a new paradigm of spintronics."-
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