Low-drift giant magnetoresistive field sensor using modulation of free-layer magnetization direction

We report a field sensor, which senses the external field by detecting the change of frequency component in the modulated GMR output. The proposed sensor works in a closed-loop mode with negative feedback and the free-layer magnetization is modulated by an alternative field Hac (2.3 Oe). The sensor output (Vout) is proportional to the applied external field (Hex) in the range from -1.5 to +1.5 Oe. Vout is determined only by the feedback current, and has no direct relationship with the magnetoresistance ratio or the gains of the amplifiers. The proposed sensor exhibits a much lower temperature drift (about 1/50) compared with a typical magnetization rotation-type sensor and a further reduction in the drift can be achieved by improving the signal acquisition circuit; thus it can be used for high-precision dc field detection without any additional temperature compensation.