Giant Magnetoresistive Sensors for Industrial Applications

摘要

Giant magnetoresistance (GMR) is the extraordinarily large change in resistance in ultra-thin magnetic multilayer films under an applied magnetic field. Its origin is spin dependent scattering in these films with layer thicknesses of only a few nanometers. Besides fundamental interest in spin dependent transport properties, the focus on these materials results from a variety of attractive applications. Here, we describe a GMR sensor concept which is tailor-made for the con-tactless measurement of angles and positions and we show the accompanied gain in performance compared to conventional Hall or Permalloy sensors. The basic scheme of this sensor is a so called spin-valve set-up. Two adjacent magnetic layers are designed such that one is magnetically hard while the other is soft. The soft magnetic layer changes the direction of its magnetisation under an applied external field with respect to the fixed magnetisation of the hard subsystem, which consists of an artificial antiferromagnet (AAF). The sensor signal, i.e. the change in resistance △R/R varies as the cosine of the angle a between the magnetisation directions in both magnetic layers.