Development of highly sensitive MI element by controlling anisotropy and noise analysis of MI element

Abstract

In order to further improve noise performance and achieve higher sensitivity, we have investigated a highly sensitive MI element by controlling anisotropy, and have analyzed noise components of a MI sensor by using a femto-tesla MI sensor system with a synchronized peak-to-peak detector. According to the results, sensitivity of a MI element decreases when tension increases. Meanwhile, sensitivity of a MI element is also linearly proportional to the ratio of impedance change and anisotropy field (∆Z/Hk). The theoretical model shows the same effect as measurement results. Furthermore, the noise of a MI sensor is considered to be mainly due to circuit noise, fluctuation of wire magnetic moment (thermal magnetic noise), and irreversible movement of a domain wall trapped by impurities and scratches on a wire surface (Barkhausen noise). The lowest thermal magnetic noise of amorphous wire calculated in our study is approximately 60 fT. Meanwhile, thermal magnetic noise and magnetic noise due to irreversible movement of a domain wall have been demonstrated as a function of the magnetic anisotropy.