Exchange interactions and giant magnetoresistance in magnetic multilayers

Abstract

Magnetic layer structures consisting of alternating magnetic and non-magnetic layers exhibit new magnetic phenomena with great potential for applications in magnetic storage technology. It is found experimentally that the magnetic moments of neighbouring magnetic layers are spontaneously aligned ferromagnetically or antiferromagnetically depending on the thickness of the intervening nonmagnetic layers. This implies an oscillatory magnetic coupling between the layers mediated by the nonmagnetic spacer layers. The resistance of the structure when a current is passed in the direction parallel to the layers is much higher in the antiferromagnetic configuration than in the ferromagnetic one. The magnetic configuration of the layers, and hence the resistance of the structure, is strongly influenced by an applied magnetic field. This effect, called giant magnetoresistance, can be exploited to read information from a magnetic disc. The purpose of this review is to introduce the reader to magnetic multilayers and to explain the underlying physical mechanisms that cause the oscillatory coupling and giant magnetoresistance.