Science & Tech

What is Magnetoresistance?

The discovery of magnetoresistance in graphene – a single-atom-thick layer of carbon atoms linked in a honeycomb pattern – by UK researchers lead by Nobel winner Andre Geim identifies this ‘wonder’ material.

The anomalous Giant Magnetoresistance (GMR) of graphene

  • At ambient temperature, graphene exhibited an abnormal giant magnetoresistance (GMR).
  • GMR is caused by magnetic fields in nearby materials affecting the electrical resistance of a wire.
  • It is found in computer hard disc drives and magnetoresistive RAM, as well as biosensors, automotive sensors, micro-electromechanical systems, and medical imagers.

What is GMR?

  • GMR is a phenomena in which magnetic fields in nearby materials alter the electrical resistance of a conductor.
  • Assume a conductor is sandwiched between two ferromagnetic materials (metals that are attracted to magnets, such as iron).
  • The electrical resistance in the conductor is low when the materials are magnetised in the same direction.
  • The resistance increases when the directions are opposite one other.

The significance of the discovery

  • In this magnetic field range, the magnetoresistance observed in the graphene-based device was over 100 times greater than that observed in other known semimetals.
  • The magnetoresistance of monolayer graphene at 27 C held between two layers of boron nitride increased by 110% under a 0.1 tesla field in the study.
  • In typical metals, the magnetoresistance increases by less than 1% under these conditions.
  • The presence of a ‘neutral’ plasma and the mobility of electrons were attributed to this by the researchers.
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