Chapter 1 Giant magnetoresistance in magnetic multilayers

Abstract

This chapter discusses the giant magnetoresistance (GMR) in magnetic multilayers. Magnetoresistance (MR) is the change in electric resistance of a conductor by a magnetic field. In nonmagnetic conductors, such as in metals like copper or gold, the MR is because of the Lorentz force that a magnetic field exerts on moving electrons. The GMR is another type of MR, existing in heterostructures and discovered in 1988 in Fe/Cr multilayers. The GMR of multilayers is induced by the variation of the angle between the magnetizations of consecutive magnetic layers. The discovery of the GMR was preceded by the discovery of exchange coupling between magnetic layers across a nonmagnetic metal layer. When a magnetic field aligns all the magnetizations in parallel, the resistance of the multilayer decreases dramatically, this was called GMR. The discovery of interlayer exchange and GMR has triggered extensive experimental and theoretical studies on multilayers and magnetic nanostructures. GMR effects are observed in exchange coupled magnetic multilayers and in uncoupled multilayers, spin valve structures, multilayered nanowires, and granular systems. GMR is used in various types of device, such as sensors, read heads, and magnetic RAM. An experimental overview that gathers results on conventional multilayers, spin valves, multilayers on grooved substrates, and multilayered nanowires are described.