Like other magnetoresistive effects, giant magnetoresistance (GMR) is the change in electrical resistance of some materials in response to an applied magnetic field. It was discovered that the application of a magnetic field to magnetic metallic multilayers such as Fe/Cr and Co/Cu, in which ferromagnetic layers are separated by nonmagnetic spacer layers of a few nm thick, results in a significant reduction of the electrical resistance of the multilayer. This effect was found to be much larger than other magnetoresistive effects that had ever been observed in metals and was, therefore, called “giant magnetoresistance”. In Fe/Cr and Co/Cu multilayers the magnitude of GMR can be higher than 100% at low temperatures.

The change in the resistance of the multilayer arises when the applied field aligns the magnetic moments of the successive ferromagnetic layers, as is illustrated schematically in the figure below. In the absence of the magnetic field the magnetizations of the ferromagnetic layers are antiparallel. Applying the magnetic field, which aligns the magnetic moments and saturates the magnetization of the multilayer, leads to a drop in the electrical resistance of the multilayer.

Since discovery in 1988 GMR has generated a lot of interest among academic and industrial laboratories due to deep fundamental physics that controls this phenomenon and tremendous technological potential for magnetic recording, storage and sensor industries. In 2007 Albert Fert and Peter Grünberg were awarded the Nobel Price in Physics for the discovery of GMR.