High sensitivity giant magnetoresistance magnetic sensor using oscillatory domain wall displacement

Abstract

A high sensitivity giant magnetoresistance (GMR) magnetic sensor has been demonstrated using the oscillatory domain wall displacing method. This sensor consists of a 30-μm-wide GMR element, CoFeB (10 nm)/Cu (2.2 nm)/CoFe (3 nm)/MnIr (10 nm), and a 100-μm-wide aluminum conducting wire placed onto the GMR element with an insulation layer between them. Domain walls in the free layer, whose easy axis is perpendicular to the length direction of GMR element, are oscillation-driven by a 140 kHz alternating magnetic field produced by an ac flowing through the aluminum conducting wire. The oscillatory wall displacement reduces the influence of wall coercivity and enables an output proportional to the external field. By applying a 1-kHz external field and separating the 1-kHz component from the amplified bridge signal using a band-pass filter, we successfully detected a magnetic field as small as 0.21 mOe (21 nT), which is much smaller than the wall coercivity of the free layer.