Biased AMR field strength sensor with small hysteresis and high stability

Abstract:
Field strength sensors based on the AMR effect require field biasing concept to guarantee a unique signal characteristic. The exchange bias approach using a natural antiferromagnetic material is an advantageous possibility to provide a field bias to the sensor. PtMn exhibits a high thermal robustness and a high blocking temperature i.e. a good exchange bias coupling even at high temperatures. However, PtMn provokes a magnetically hysteretic behavior of the AMR layer. An antiferromagnetic interlayer coupling to an additionally introduced directly exchange bias coupled pinned layer significantly reduces the observed magnetic hysteresis. By adapting the interlayer coupling and the thickness of the pinned layer the hysteresis as well as the linear range of the sensor can be modified. The experimental findings will be qualitatively explained by a Stoner-Wohlfarth model.