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The five-layered graphene displayed a mix of unique magnetic and electronic properties, which could be used to design more efficient storage devices.
Scientists are continuing to discover new properties about the ‘wonder material’ graphene, with a new study suggesting it can take on unique electronic behaviour when arranged in specific layers.
Graphene is an incredibly strong, thin material, being a one-atom-thick layer of carbon that is 200 times stronger than steel. The flexible and conductive properties of graphene also give it a wide range of potential applications.
Now, an MIT study suggests that stacking graphene in five layers in a specific pattern causes it to take on a “multiferroic” state, where it displays both unconventional magnetism and a specific type of electronic behaviour.
The team said a ferroic material is one that displays some coordinated behaviour in its electric, magnetic or structural properties. For example, electrons in a magnet coordinate to spin in the same direction without an external magnetic field.
Multiferroric materials, meanwhile, display multiple properties that can coordinate to exhibit multiple preferred states. A hypothetical example of this would be if the electric charge of a magnet shifted in a direction independent of the magnetic direction.
Efficient storage
The MIT team said multiferroic materials are rare and have potential applications in electronics because they could increase the speed of hard drives while lowering the energy cost.
Magnetic hard drives consist of microscopic magnets that read as either one or zero, depending on their magnetic orientation. These magnets are switched by electric currents. But if a storage device was made with multiferroic material, the study suggests these magnets could be switched by a faster, more efficient electric field.
“Having multiferroic properties in one material means that, if it could save energy and time to write a magnetic hard drive, you could also store double the amount of information compared to conventional devices,” said assistant professor of physics at MIT Dr Long Ju, who led the study.
In terms of the two unique properties, the layered graphene’s electrons coordinated their orbital motion, which the team said was like planets circling in the same direction.
The second property was how the graphene’s electrons reacted to electronic “valleys”, which are the lowest possible energy states that an electron can settle into – graphene has two possible valleys. But in five-layer graphene, the electrons coordinated and would prefer to settle in one valley over the other.
In the study, the team claimed to be able to control both the magnetism and the unique electronic properties that the layers of graphene displayed. The team also noted that the graphene didn’t display this unique electronic behaviour – which they called ferro-valleytricity – and the unconventional magnetism combination until it was arranged in five layers.
“Graphene is a fascinating material,” Ju said. “Every layer you add gives you essentially a new material. And now this is the first time we see ferro-valleytricity, and unconventional magnetism, in five layers of graphene. But we don’t see this property in one, two, three or four layers.”
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