金属纤维磁性控制及不对称巨磁阬效应机制研究

Giant magneto impedance, GMI effect has become hot topics in design of magnetic sensors for its high sensitivity of weak magnetic field detection capacity. In order to improve the sensitivity and linearity, it is necessary to limit the symmetry of the impedance near zero magnetic field, and to obtain the asymmetric GMI , AGMI effect. This project is to investigate effective available method to stimulate AGMI effect in Co-based metallic fibers through the different annealing process combined with various status of stresses, which can optimize domain structure of soft magnetic materials, and control the horizontal permeability by magnetic elasticity energy to obtain AGMI effect. The influence of magnetic elasticity on phase evolution process and transformation of domain structure during stress annealing treatment is analyzed with the basic mathematic model. The physical mechanism of magnetic elasticity on modification of domain structure is discussed by magnetic energy analysis. GMI effect of Co-based metallic fibers before and after annealing is investigated to build the optimal magnetic control technology and to achieve high sensitivity AGMI effect. Through the implementation of this project, the fundamental theory of domain structure evolution under magneto elastic energy is clear and an available AGMI effect with high linearity and high sensitivity technology is created without additional power consumption.

巨磁阻抗(Giant Magneto Impedance ,GMI）效应在弱磁检测方面的高灵敏度使之成为磁传感器研究的热点。为了提高灵敏度和线性度，需要限制阻抗在零场附近的对称性，获得不对称GMI（Asymmetric GMI，AGMI）效应成为关键。本项目以Co基金属纤维为研究对象，通过退火过程中不同状态、强度应力的施加，利用磁弹性能优化软磁材料的畴结构，控制这类材料的横向磁导率，获得AGMI效应。结合退火中的磁弹性能对相变过程的影响，建立应力退火畴结构演变基本数学模型，探讨控制磁性能的基本方法，明晰弹性应变能影响退火畴结构的物理机制；分析不同应力退火前后的GMI效应，研究应力强度、温度、施加方式等对GMI效应的影响，建立最优的磁性控制技术，从而获得高灵敏度AGMI效应。通过本项目研究，确定磁弹性能影响畴结构根本理论，创建无额外功耗、高线性度、高灵敏度的AGMI新技术。

项目以软磁金属纤维、金属薄带为研究对象，设计了焦耳退火工艺，分析了退火前后材料的组织结构、磁畴结构、磁性能和巨磁阻抗(Giant Magneto Impedance ,GMI)效应，获得了纤维和薄带不对称GMI(Asymmetric GMI,AGMI)效应的基本条件和物理机制。研究表明焦耳退火对软磁材料各向异性的影响是决定材料GMI特征的重要因素之一，焦耳电流密度较低时，焦耳热改变了磁弹性场，使得内部应力分布进一步均匀，在磁弹性场和焦耳电流产生磁场的共同作用下，磁畴逐渐转变带状畴，且逐渐细化，磁化阻力降低，有利于提高GMI效应和磁场响应灵敏度；焦耳电流密度较高时，晶化开始，硬磁相的形成和长大提高了局部磁晶各向异性，并导致不同磁性相间的磁耦合作用，从而改变了材料的各向异性；且大的退火电流作用下，矫顽力提高，GMI效应虽然提高，但不利于磁场响应灵敏度的增强。焦耳退火中应力场的存在，磁弹性能的增加使得磁畴向磁弹性场方向偏转，材料的螺旋/横向各向异性进一步提高，材料的低频GMI效应增强，灵敏度也大大提高；纤维状材料螺旋各向异性的存在，使材料对偏执磁场更敏感，适当的偏执电压更容易诱导优异的AGMI效应，灵敏度大大提高；但带状材料的横向各向异性的改变更容易获得低频AGMI效应，对激励条件也更加敏感。另外，研究表明外磁场作用下材料的易轴方向决定了其GMI效应最大灵敏度出现的工作点，但为提高传感器的稳定性需避免最小易轴角附近选择工作点，因此，控制材料的各向异性改善其磁化过程是改善GMI效应的关键。