Giant magnetoresistance (GMR) magnetic field sensors have been widely used in many applications such as hard-disk-drive heads, linear/rotary position sensing, and biomagnetic sensing. Compared to various other magnetic sen- sors, the GMR sensor has a high-frequency response, over 1 MHz, and can be easily integrated onto one chip. However, typical GMR sensors show lower field resolution than other sensors such as fluxgate and magneto-impedance sensors. Most of the spin-valve GMR sensors only utilize the rotation of free-layer magnetization to detect the external magnetic field. For this type of sensors, a bias field is applied to saturate the free-layer magnetization along the easy axis and the external field is detected along the hard axis.
    Our group introduces a novel GMR magnetic field sensor which utilizes the oscillatory domain wall displacement (DWD) of the free layer to detect the external field. Since the domain wall displacement is quite sen- sitive to the external field, and moreover, the oscillatory domain wall displacement reduces the influence of the wall coercivity and Barkhausen effect, higher sensitivity compared to the conventional GMR sensors is expected.
    By carrying out the fundamental sensor experiments using the developed sensors, a minimum field of 8-nT was detected using the DWD GMR sensor. The field sensitivities of the DWD GMR sensors were 2.73 mV/(V Oe), which is higher sensitivity than the conventional magnetization rotation type sensors, and further improvement of the sensitivity by optimizing the free layer material and/or by using a magnetic tunnel junction is expected.

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