Almost 20 years after graphene’s discovery, research suggests it is the most magnetoresistant material we know of. This describes its ability to increase or decrease its electrical resistance in response to a magnetic field, which could one day have applications for how we store data.
Arranged as a sheet of carbon atoms in a honeycomb-like structure, graphene – a two-dimensional material extracted from graphite – was already known to be stronger than diamond and able to conduct electricity better than copper.
Now, Andre Geim at the University of Manchester, UK, and his colleagues have discovered that it also has unprecedented magnetoresistance at room temperature.
To uncover this, the team first applied an electric field to some graphene to equalise the number of its charge carriers, which are responsible for creating a material’s electric current. These carriers are made up of electrons, which have a negative charge, and holes, which have a positive charge.
Pristine graphene, which has no flaws to its honeycomb structure, has equal numbers of electrons and holes. Since it is difficult to produce such graphene, the researchers used an electric field to adjust the structure of flawed graphene, enabling them to research the material in a more pristine state.
Flaws in the material’s structure affect its magnetoresistance, says Geim, who won the 2010 Nobel prize in physics for his research into graphene.
Next, the researchers applied different magnetic fields to the graphene to measure how its magnetoresistance changed. Even when applying small magnetic fields, its electrical resistance changed dramatically.
This is partly down to graphene’s electrons and holes being highly mobile and therefore sensitive to small changes to an external magnetic field, the researchers write in their paper.
Most materials only display magnetoresistance at very low temperatures. In this experiment, graphene was more magnetoresistant at room temperature than any other material, such as graphite and bismuth, tested in previous studies, according to the researchers.
Magnetoresistant materials are already used in data storage devices to interpret information that is stored as small magnetic patterns on a tape or disc. The researchers plan to continue to study graphene and its “applications will follow”, researcher Leonid Ponomarenko at Lancaster University, UK, said in a statement.
Antonio Helio Castro Neto at the National University of Singapore says the discovery could open doors in exploring fundamental physics.
Because graphene is a two-dimensional material, the motion of these charge carriers is confined to a thin layer, he says.
“In this regime, the interactions between holes and electrons become extremely strong and there is room to control these interactions and study what’s governing them further,” says Castro Neto.