Influence of the free-layer domain structure on domain-wall displacing type field sensors

Abstract

We propose a giant magnetoresistive sensor which utilizes the shifting of oscillatory domain walls to detect the external field along the easy axis. For this type of sensor the domains in the soft magnetic free layer play an import role and the sensor output is mainly determined by the domain-wall displacement. Domain structures in various micro-fabricated soft magnetic patterns have been investigated and two typical free-layer materials were selected to fabricate the sensor devices. The domain-wall displacing (DWD) type sensor with a 10 nm Ni80Fe20 free layer shows a higher field sensitivity than that with CoFeB, however the sensor output becomes saturated when the external field (Hex) > 0.4 Oe. For the sensor which has a 10 nm (Co90Fe10)92B8 free layer, the sensor output is linear even as Hex increases to 2.6 Oe. In addition, the sensors were operated under the magnetization rotation mode to compare the sensor outputs with the DWD mode. When the sensors were operated under the DWD mode a field sensitivity of at least two times higher was achieved.