Graphene, a sheet of carbon just one atom thick, is a promising material for making molecular electronic devices of the future thanks to its unique electronic and mechanical properties that include extremely high electrical and thermal conductivity and exceptional strength. Room-temperature ferromagnetism can now be added to this already impressive list.

Sakhrat Khizroev at Florida International University and colleagues made their discovery thanks to detailed low-temperature magnetotransport and superconducting quantum interference (SQUID) measurements, and vibrating sample magnetometry (VSM) on graphene samples functionalized with nitrophenyl (NP) groups. The material studied appears to become an organic molecular magnet with ferromagnetic and antiferromagnetic ordering that persists at temperatures above 400 K.

The team, which includes Jeongmin Hong at UC Berkeley, Robert Haddon at UC Riverside and Walt de Heer at the Georgia Institute of Technology, has been working on these experiments since 2008. "We believe that the NP groups act to unpair electron spins at periodically spaced carbon sites along certain graphene orientations, known as 'armchair' and 'zigzag'", Hong told nanotechweb.org. "It is the interactions between these unpaired spins that lead to the magnetic order we observed."

Graphene functionalized with hydrogen also appears to have similar magnetic properties, he added.

"Ours is a 'gentle chemistry' approach that makes use of functionalization rather than introducing defects into graphene, which is a much more aggressive strategy," he explained. "Although previous research mainly looked at heavily defected material, large numbers of defects in graphene can hinder the formation of the pure zigzag edges needed for magnetism here."

According to the researchers, the NP-functionalized graphene could be used as a novel single-layer magnet. It might also be used to make new types of spintronics devices based entirely on carbon that exploit the unpaired spins present. Spintronics is a relatively new technology that exploits the spin of an electron as well as its charge.

More details about the research can be found in ACS Nano.

Further reading

Magnetic defects upset graphene electron spins (May 2013)
Graphene goes magnetic (Nov 2011)
Graphene nanoislands go magnetic (Dec 2007)