What is magnetoresistance? It’s one more thing graphene does differently. Premium

Researchers led by Nobel laureate Sir Andre Geim have discovered that graphene displays an anomalous giant magnetoresistance at room temperature, leading to potential applications in magnetic-field sensing in extreme environments.

Researchers in the UK, led by Nobel laureate Andre Geim, have discovered another property of graphene – a single-atom-thick layer of carbon atoms bonded in a honeycomb pattern – that further distinguishes this ‘wonder’ material.

Dr. Geim & co. found that graphene displays an anomalous giant magnetoresistance (GMR) at room temperature.

GMR is the result of the electrical resistance of a conductor being affected by magnetic fields in adjacent materials. It is used in harddisk drives and magnetoresistive RAM in computers, biosensors, automotive sensors, microelectromechanical systems, and medical imagers.

GMR-based devices are particularly used to sense magnetic fields. The new study has found that a graphene-based device, unlike conventional counterparts, wouldn’t need to be cooled to a very low temperature to sense these fields. The finding was published in Nature on April 12.

Say a conductor is sandwiched between two ferromagnetic materials (commonly, metals attracted to magnets, like iron). When the materials are magnetised in the same direction, the electrical resistance in the conductor is low. When the directions are opposite each other, the resistance increases. This is GMR.

The magnetoresistance observed in the graphene-based device was “almost 100-times higher than that observed in other known semimetals in this magnetic field range,” Alexey Berdyugin, assistant professor of physics at the National University of Singapore and the paper’s coauthor, told The Hindu by email.

The effect is due to the way electrons in the conductor scatter off electrons in the ferromagnets depending on the orientation of the latter’s spin, which is affected by the direction of the magnetic field.