基于纳米晶梯度结构的CoFe基非晶微丝巨磁阻抗性能调控机制研究

The Giant Magneto-impedance effect of microwires has important application significance in weak magnetic detection and sensor miniaturization. However, there exists bottlenecks problems, which are the low impedance ratio and field sensitity of GMI materials in traditional tailoring method. For this research program, we choose the CoFe-based amorphous microwires for proceeding medium DC pulse current annealing to build the nanocrystalline gradient-structure and simultaneously induce circular magnetic field to tailor the surface domain structure, thus obtaining the strategy and mechanism for the enhancement of GMI properties. The whole idea is briefly stated as follows: Firstly, based on the conductivity of crystal material higher than amorphous, we increase the conductivity in core area of microwires then enhance the skin effect depth through the nanocrystalline gradient distribute in radial direction. Secondly, the Joule energy temperature is controlled below the Curie point for cooperating with the induced circular magnetic field to tailor the surface domain structure, and then enhance the anisotropy of microwires. Finally, the amorphous structure is retained on the shell area of microwire for preventing the pinning effect induced by nanocrystal. This research program is based on nanocrystalline gradient-structure and surface domain-structure tailoring, focusing on the research of the nanocrystalline precipitation behavior, radial distribution rule, axial angle of cyclic magnetic domain and average value of leakage magnetic field. Thus, the influence law of skin depth and anisotropy for the performance of GMI is expounded, then the improve mechanism of microstructure evolution is revealed. In a word, we will realize the significant improvement of the GMI performance of amorphous magnetic sensitive materials, and provide experimental data and theoretical basis for the development of micro-GMI sensor to detect the ultra weak magnetic field.

巨磁阻抗效应在新兴弱磁探测及磁敏元件微型化等方面具有重要意义，但遗憾的是关于巨磁阻抗性能调控机制的研究仍不完善。本项目以CoFe基非晶微丝为研究对象，通过在介质中的脉冲电流处理，调控纳米晶梯度结构及表面磁畴结构，探讨提高巨磁阻抗性能的途径与机制。主要思路为：在非晶基体构建沿径向纳米晶尺寸与数量递减的梯度结构，增加径向电导率差值，提高趋肤深度；控制表层处理温度低于居里点，协同环向感生磁场调控表面磁畴结构，提高环向磁各向异性；同时，因其可保留表层非晶态结构，有效避免纳米晶对磁畴的钉扎作用。本项目在梯度结构设计基础上，通过纳米晶析出行为、径向分布规律、环向磁畴轴向角及平均漏磁场强度等方面的研究，阐明趋肤深度及磁各向异性对巨磁阻抗性能的影响规律，揭示提高巨磁阻抗性能的微观结构调控机制，实现非晶微丝巨磁阻抗性能大幅提高，为促进非晶微丝在微型磁电传感器新兴弱磁探测领域中的应用，提供实验依据及理论支撑。

本项目基于正混合焓Cu元素的掺杂设计改变CoFe基非晶成分热物性参数及其GFA，结合熔体抽拉参数调控即抽出层及液态微丝接触表面及自由表面的热量传输及冷却速度差异，在非晶微丝表面构建纳米晶结构等有序组织，同时非晶微丝内部仍为非晶态；获得了非晶（芯部）-纳米晶（表层）复合结构微丝构建所需的成分及制备参数调控规律及梯度复合结构非晶微丝巨磁阻抗性能以及力学可靠性调控机制；证实了径向的热能不均匀分布可调控微丝的纳米晶析出行为进而控制其巨磁阻抗性能及力学性能。.进而选取GFA降低的Cu掺杂非晶微丝结合直流介质电流处理处理，结合电流处理瞬态升温曲线及微丝晶化点、居里温度等热物性参数，设计不同电流幅值及时间组合，模拟微丝径向热量分布，调控内部晶化区域半径，成功制备出不同厚度比例的纳米晶（芯部）-非晶（表层）梯度复合结构微丝复合结构。对比分析制备态非晶（芯部）-纳米晶（表层）复合结构微丝，获得热量分布对微丝纳米晶等有序组织的析出行为的调控机制，通过原位分析有序组织带来的表面形貌及瑞利波等参数的变化对表面微磁结构及趋肤深度的影响规律，进而阐明了焦耳热激活能及环向磁场能协同作用通过电导率及磁导率对非晶微丝巨磁阻抗性能的调控机制，获得了CoFe基非晶微丝获得优异巨磁阻抗性能的纳米晶梯度复合结构调控方案。.本项目同时对CoFe基非晶微丝磁敏传感器应用所需的应变效应及力学可靠性进行了深入系统研究。通过不同梯度复合结构拉伸失效曲线的多参数模型力学统计分析，获得了其可靠性调控的影响规律与机制。并创新性的采用了原位视频引伸计对对CoFe基及Fe基非晶微丝在不同应变速率下单轴拉伸应力-应变行为进行对比分析，发现微丝的断裂可靠性主要取决于断裂面上剪切偏置特征长度的平方根奇异性，满足线弹性断裂力学。发现CoFe基微丝呈正应变效应，首次将断裂行为分4个主要阶段，并通过缺少锯齿流变的纯滑移区域分析预测，提出了剪切带扩展中自由体积抵消机制。