Study On GMI Effect In Amorphous Alloys And Novel Weak Magnetic Field Sensor

In this thesis, theory and experiment of giant magneto-impedance (GMI) effect have been studied systematically. Based on the study above, a novel weak magnetic sensor is developed using the GMI effect of annealed C0_66.3Fe_3.7Si₁₂B₁₈ amorphous alloy ribbon. The main results are summarized as the followings:The detailed expressions of orientation-related relative permeability in amorphous alloy ribbon under applied driving ac current flowing through the ferromagnetic materials and dc external magnetic field are derived by Simultaneously solving the Maxwell's equations and the Landau-Lifshitz equation of motion and establishing the magnetic domain structure model. The calculation formula of mean relative permeability averaging over 90 orientation angle and the magneto-impedance are obtained.The GMI effect of Co_66.3Fe_3.7Si₁₂B₁₈ amorphous ribbon dependence on driving current is studied. The experimental results show that GMI response presents symmetric double-peak behavior. The maximal magneto-impedance ratio (GMI)_max and magnetic field sensitivity closely relate to driving current frequency. They reach their maxima at a certain frequency respectively. The increase of the driving current amplitude is beneficial to the improvement of (GMI)_max. However, the maximai magnetic field sensitivity is obtained at a current amplitude. The applied field corresponding to the impedance peak moves to higher magnetic field scope with the increase of the driving current frequency and amplitude.The influence of pulsed current annealing on the GMI effect of Co_66.3Fe_3.7Si₁₂B₁₈ amorphous ribbon is studied. The obtained results show that the GMI effect is closely connected with annealing current density. With the increase of annealing: current density, the (GMI)max increases at first, then reaches the maximum and finally decreases. The effect of transverse anisotropy field H_K induced by annealing on the GMI effect is also analyzed.A weak magnetic field sensor based on GMI effect is developed by using Co_66.3Fe_3.7Si₁₂B₁₈ amorphous ribbon annealed by pulsed current. The operation principle of the sensor is analyzed. The signal processing circuit is designed and sensor calibration is also performed. The measurement range and linearity of the sensor are improved by designing negative feedback forming closed-loop system. The main factors affecting the performance of sensor are analyzed.The sensor can be used in the weak magnetic measurement field including earth magnetic field and environmental magnetic field.