LAKE WALES Fla.—By inserting hydrogen atoms into the lattice of a graphene sheet, researchers from Spain and Egypt say an array of electrons in nanoscale domains encoded with magnetic spin can transform the material into a spintronic successor to silicon.
Graphene, predicted to be the successor to silicon at the end of the International Technology Roadmap for Semiconductors (ITRS) circa 2023, is missing a key ingredient: magnetism. Although silicon has gotten by without significant magnetic properties, beyond the end of the roadmap, information is going to have to be stored on the magnetic spin of individual electrons (rather than accumulations of charge). Using magnetic-spin allows electrons to stand for both 1s and 0s depending on their spin direction—up or down—the basis of spintronics.
Now researchers think they have solved the magnetic-graphene problem by inserting (doping) hydrogen atoms into specific locations in the graphene lattice. If it works, electronics will never be the same since hydrogen has only a single electron making it the densest possible spintronic material. By spreading out hydrogen atoms in an already tightly packed array of carbon atoms (graphene) spintronic circuits could be built at ultra-small nano- or even angstron-scale (10 angstroms equals a nanometer).
"We visualize, for the first time, how the absorption of single hydrogen atoms on graphene magnetizes the graphene regions around them. In contrast to common magnetic materials, where the magnetic moments are localized in a few angstroms, the induced graphene magnetic moments extend over several nanometers and present an atomically modulated spin texture," professor Ivan Brihuega at the Cooperative Research Center (CIC) nanoGUNE (Basque, Spain) told EE Times.
Because there influence spreads out from angstroms to nanometers Brihuega claimed that spintronic circuits might be made by using their induced magnetic moments to couple strongly with other nearby spintronic circuit elements following a particular rule his team discovered: namely, that magnetic moments sum-up or neutralize depending on the relative locations of the two adjacent hydrogen adsorption sites.
"Furthermore, and equally important, we achieved the controlled manipulation of single hydrogen atoms, which enabled us to selectively tune the collective magnetic properties of chosen graphene regions," Brihuega told EE Times.
Graphene actually has two sub-lattices intertwined, according to the researchers, one of which allows addition of magnetic spin over short distances and the other of which cancels out magnetic spin over similar distances. Likewise if spin directions in the same sub-lattice are opposite, they they attract, and if they are the same, repel. The researches also observed a modulation effect in certain configurations. Using all these properties together, by placing hydrogen atoms in highly selective locations in each sub-lattice, the researchers hope to build atom-scale spintronic circuitry.
Magnetism completes graphene
"Ever since 2004, when it was first possible to obtain graphene for experiments, laboratories around the world have been trying to add magnetism to the long list of properties of this purely two-dimensional material," Brihuega told EE Times.
The reason, he claimed, was that graphene is "a priori" [independent of experimentation] an ideal material for use in spintronic technology, promising to replace traditional silicon electronics by transmitting both magnetic and electronic information at the same time. As a result, a new generation of more powerful computers could both process and memorize information simultaneously, as does the human brain.
"So the results obtained in this work, which indicate the possibility of freely generating magnetic moments in the graphene and showing how these moments can communicate with each other over great distances, is paving the way for a promising future for this material in the emerging field of spintronics," Brihuega told us.
The theoretical foundation is formed so that now comes the time-consuming engineering characterization and innovation steps needed to transform laboratory curiosities into real world technologies, which may take until 2023 as predicted by the ITRS.
"Our current experiments were performed at five degrees Kelvin, so our next step will be trying to find the highest possible temperature at which graphene can become magnetic by the adsorption of hydrogen atoms," Brihuega told us.
Then comes the really difficult step of using graphene magnetism in a real world spintronic device. Ordinarily that step could take decades, but Brihuega is optimistic that it will not take that long.
"In a standard material, the normal answer would be that it will take quite some time; however, graphene has already been shown to be anything but standard, and one should not be very surprised to see such a device soon," Brihuega hinted about work he already has in progress.
For all the details, read Atomic-scale control of graphene magnetism by using hydrogen atoms.
— R. Colin Johnson, Advanced Technology Editor, EE Times