Giant Magnetoresistance (GMR) is a phenomenon in condensed matter physics discovered by Albert Fert and Peter Grünberg in 1988. It involves a significant change in the electrical resistance of a material in the presence of a magnetic field. The discovery revolutionized the field of magnetoelectronics and had profound implications for information storage technology.

GMR occurs in multilayered structures composed of alternating ferromagnetic and non-magnetic thin layers. When subjected to an external magnetic field, the relative orientation of the magnetic moments in adjacent ferromagnetic layers influences the overall electrical resistance of the structure. The resistance is minimized when the magnetic moments are parallel and maximized when they are antiparallel. This property is exploited in GMR devices, such as read heads in hard disk drives, enabling high-density data storage with improved sensitivity and efficiency.