Designing a giant magnetoresistance field sensor via inferences from a giant magnetoresistance hysteresis model

By using a model for giant magnetoresistance (GMR) hysteresis and a model f or Barkhausen noise, a magnetic hysteresis model is used to map the effects of magnetic hysteresis on GMR and on accompanying magnetic noise in a GMR magnetic field sensor. Two magnetic noise sources potentially exist in the field sensor: (1) the GMR multilayer material and (2) permalloy field conce ntrators. The GMR material typically shows a coercivity at H(c)congruent to 1 kA/m, much larger than H-c=0.012 kA/m of permalloy. Because permalloy ha s a very large maximum permeability, it is a much larger magnetic noise sou rce than the GMR material, and would greatly affect sensor operation if ope rated near H=0. By operating with a bias field well above 1 kA/m, one can o perate away from both noise sources. Because the increasing and decreasing arms of the magnetic hysteresis tail of the GMR material are each approxima tely proportional to \H\(1/2) over a large field range, the model shows tha t increasing and decreasing portions of the GMR vs H hysteresis curve turn out to be linear, parallel to each other, for the operating field region. I f the GMR curve is linear in a region away from H-c, a bias field operation in this range would mean that the sensor would not only be nearly noiseles s (save for Johnson noise) but also would exhibit linear change in field un der an applied field H and could easily be calibrated to measure H. Thus, t he modeling points the way to low noise GMR field sensor design. In practic e, it is found that biasing at fields halfway down the GMR curve does indee d produce a much quieter measurement than near zero bias field. (C) 2000 Am erican Institute of Physics. [S0021-8979(00)32908-5].