Graphene made magnetic with hydrogen coating

PORTLAND, Ore. — Graphone, a new magnetic version of carbon monolayers called graphene, could enable a new breed of carbon spintronic devices, researchers claim.

Graphene, consisting of pure crystalline carbon sheets, cannot be doped with impurities to adjust its semiconducting and magnetic properties as easily as silicon since carbon does not readily "heal" implantations with annealing. Rather than implanting dopants, researchers say, a surface treatment can be used to adjust a carbon sheet's properties.

Researchers say hydrogen can be used to fine-tune graphene's metallic, semiconductor and magnetic properties, resulting in either graphene (metallic), graphane (semiconducting) or graphone (ferromagnetic).

"Dangling bonds of carbon carry a magnetic moment, and these can be aligned ferromagnetically," said professor Purusottam Jena of Virginia Commonwealth University in Richmond. "When graphene is fully saturated with hydrogen, all the dangling bonds disappear and conducting graphene turns into a wide bandgap semiconductor. When only half the carbon atoms are saturated with hydrogen the system becomes ferromagnetic, but magnetism disappears at 25 percent hydrogen coverage."

Crystalline carbon monolayers called graphene can be made ferromagnetic, called graphone, by adjusting the amount of hydrogenation on their surface, according to researchers.

Previous experiments confirmed that hydrogen surface treatments on graphene sheets can adjust metallic properties to become a semiconductor. Jena's group is the first to claim that partial hydrogenation can also adjust graphene to become ferromagnetic, or graphone. Unlike graphene ribbons, which adjust their semiconducting and magnetic properties by forming zig-zag edges, graphone's ferromagnetic properties extend over the entire sheet.

The researchers predict that if graphene is half-hydrogenated, then carbon molecules lacking a hydrogen atom will be localized and unpaired. This gives them an adjustable magnetic moment that can couple ferromagnetically, thereby allowing the property to be harnessed in semiconducting devices.

By adjusting the coverage of hydrogen on the surface, the researchers propose adjusting graphene's properties for future spintronic devices that store information in the magnetic moment of carbon molecules.

"Our next step is to examine such phenomena on other single-layered materials such boron nitride [while studying] the effect of other ligands such as fluorine on magnetic and electronic properties," said Jena.

The researchers further claim that the structural integrity and magnetic homogeneity of graphone sheets should be comparable with the desirable mechanical properties of graphene. They are awaiting experimental confirmation that their theoretical recipe for making ferromagnetic carbon sheets works as simulations predict.