Monday, March 9, 2009

Giant Magnetoresistance

Giant magnetoresistance is the change in electrical resistance of some materials in response to an applied magnetic field. 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.

Giant Magnetoresistance is a very large change in electrical resistance that is observed in a ferromagnet/paramagnet multilayer structure. Resistance change occurs when the relative orientations of the magnetic moments in alternate ferromagnetic layers change as a function of applied field. 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.