Magnetoresistance

The magnetoresistance is a property that certain materials have to vary their electrical resistance when they are subjected to a magnetic field.

This effect was discovered by William Thomson in 1857, although he was not able to decrease resistance by more than 5% (today it is up to 600%).

Recent research has led to the discovery of materials that present GMR effect (giant magneto-resistance:, 'giant magneto-resistance'), CMR effect (colossal magneto-resistance: 'colossal magnetoresistance') and TMR effect (tunnel magneto-resistance: 'tunnel magnetoresistance').

Both MR and GMR are based on the spin of electrons and are therefore part of spintronics.

Modern computers make use of this property. Hard drives use the giant magnetoresistance. The reading heads of hard disks are composed of a group of elements such that their electrical resistance depends on the magnetic field. The "bits" on a hard drive are held like a small magnet. The electrical read head has an electrical resistance (MR) that varies when it passes over the "little magnet" that is a bit. Therefore, when a bit passes under the read head there is a change in resistance that can be easily detected.