Magnetoresistance is the property of some materials to lose or gain electrical resistance when an external magnetic field is applied to them. The effect was first discovered by William Thomson in 1857, but he was unable to lower the electrical resistance of anything by more than 5%. But now materials showing giant magnetoresistance (GMR), colossal magnetoresistance (CMR) and magnetic tunnel effect (TMR) are known.

Anisotropic magnetoresistance (AMR) A material property leading to the increase of electrical resistance when the direction of current is parallel to the applied magnetic field. Discovered by Lord Kelvin this effect is only found in ferromagnetic materials and is resultant from changes to the orientations of the electron orbitals.