Giant Magnetoresistance in Magnetic Layered and Granular Materials

Publisher Summary Magnetoresistance (MR) is the change in electrical resistance of a material in response to a magnetic field. All metals have an inherent, albeit small, MR owing to the Lorentz force that a magnetic field exerts on moving electrons. Although earlier studies reported unusual magnetoresistive effects in layered structures, it was discovered that the application of magnetic fields to atomically engineered materials known as magnetic superlattices greatly reduced their electrical resistance, that is, superlattices had a giant magnetoresistance. Superlattices are a special form of multilayered structures, artificially grown under ultrahigh-vacuum conditions by alternately depositing on a substrate several atomic layers of one element, say, iron, followed by layers of another, such as chromium. The original observation of giant magnetoresistance was made on iron–chromium superlattices with nearly perfect crystallinity, which was grown by molecular beam epitaxy (MBE). Giant magnetoresistance observed in layered and granular structures arises from the dependence of the resistivity on their internal (local) magnetic configuration.