Experiments on the Perpendicular Giant Magnetoresistance in Magnetic Multilayers

Abstract

Since the discovery of the Giant Magnetoresistance (MR) effect in Fe/Cr magnetic multilayers [1], most of the experiments have been carried out with the measuring current in the plane of the multilayer, the so-called Current-In-Plane (CIP) geometry. The reason is simple: it is very easy to measure the fairly large resistance of a thin film or multilayer with the current in the plane of the sample because the length of the sample is typically orders of magnitude larger than the film thickness. The opposite is true for the situation where the measuring current is perpendicular to the multilayer plane (the so-called CPP geometry): the length of the sample is determined by the layer thickness which is usually much smaller than the typical lateral dimension. So one needs extremely sensitive measuring techniques to measure ultra-small resistances or nano- and microfabrication technologies to reduce the cross-section of the sample, giving rise to resistances that can be measured by conventional methods. Despite these experimental difficulties, the perpendicular MR effect appeared particularly attractive to experimentalists, because it typically is a factor two to five larger than the corresponding current-in-plane MR effect. This makes the subject of interest both for fundamental physical reasons and also for possible applications.