Giant Magnetoresistance (GMR)
Effects such as the giant magnetoresistance effect (GMR) occur only in artificial multilayer structures. For example, two magnetic layers of iron that communicate (couple) with each other via an intermediate film. For the occurrence of the GMR effect, the mid-layer consists of a non-ferromagnetic, electrically conducting material such as chromium. This layer must only be a maximum of a few nanometres in thickness and its interfaces must be of the very best quality. Such a "sandwich" structure changes its resistance by more than 50 percent while exposed to an external magnetic field. GMR stacks are found in highly sensitive magnetic field sensors, and are used for example in read heads of computer hard disks. In future, these structures will be employed in anti-lock braking systems and in many other automotive applications, or for the readout of biochips.