针对磁性复合结构的透射电镜表征新技术与磁畴三维立体结构的高分辨研究

Magnetic composite structures, such as nano-magnetic core/shell materials, have important applications in drug delivery fields. However, due to a strong magnetic filed (2 Tesla) generated from the objective lens of transmission electron microscope (TEM), it is very difficult to observe magnetic materials with high-resolution, moreover, the saturated specimen with single-domain structure lost the initial magnetic structure information. This project aims at establishing a set of advanced and efficient TEM method and technique for the characterization of magnetic composite structures. Both high-resolution observing magnetic materials and accuratly analyzing the initial magnetic states of magnetic specimens can be achieved. Transforming from the conventional TEM observing mode into free-lens-controllable mode, to avoid of the influences of objective lens, to re-combine each lens data and to study the electron optics under this imaging condition, hig-resolution/high-quality Lorentz images could be obtained. By 3D tomography reconstruction technique and Lorentz imaging, the 3D morphology of magnetic domain will be investigated.By electron holography techniques, the residual magnetic flux density (Br) and other megnetic properties of many types of mmagnetic composite structures could be quantitatively studied. Combining the novel electron magnetic chiral dichroism technique and large-angle converage beam diffraction mode,the quantitative spin electron states of transitional-group-elements around core,interface, and shell regions and qualitative analysis of Bloch wall and Neel wall will be carried out. Via in situ technique of applying megnatic field inside TEM, the response behavior of domain wall to the applied field will also be studied.Via in situ flowing reaction atomosphere, the growth mechanism will be investigated.

磁性复合结构，如纳米核壳材料在药物附载等领域具有重要应用。但由于透射电镜的物镜会产生约2T的强磁场，磁性材料的高分辨观察很困难，被单畴化的样品更是缺失了原始的磁畴结构信息。本课题旨在探索发展一套先进的、基于透射电镜的针对磁性复合结构的表征方法与技术，既能高倍率观察磁材料结构，也能准确分析其真实磁畴状态：改变传统观察模式为关闭物镜的自由透镜模式，重组各级透镜参数并研究该成像条件下的电子光学，以得到高质量/高倍数的洛伦兹显微像；研究磁材料的超显微结构，包括：利用三维重构技术与洛伦兹成像，研究磁畴的三维立体形态；利用电子全息技术，定量分析各类磁性复合结构的剩余磁化强度等磁性质；结合新颖的磁圆二向色性和大角度会聚束电子衍射，定量分析核、界面、壳、膜面等区域的过渡族元素的电子自旋状态、并定性分析布洛赫壁、尼尔壁等磁畴壁结构；在电镜中原位加磁场，研究畴壁对外场的响应规律；原位通入反应气，研究生长机理。

严格按照任务书要求开展工作，在以下几个方面取得突破：解决了由于透射电镜物镜存在强磁场而很难清晰分析金属磁性材料的微观结构的难题，改造透射电镜物镜系统实现消磁，突破了常规洛伦兹透射电镜的极限分辨率，自主建立了针对金属磁性材料的原位低温多场耦合电镜研究平台，以此平台为基础在原子分辨显微结构角度研究了磁性材料的电磁结构与性能的构效关系，取得了多项创新性研究成果。建立洛伦兹高倍观察的电子光学，包括建立消磁模式下且关闭物镜的自由透镜模式、重组各级透镜参数、建立原位低温加电磁场的电镜表征平台，申报2项国家发明专利。基于此平台，综合运用多种先进显微学分析技术，如磁圆二向色性、会聚束衍射、电子全息、三维重构、电子能量损失谱等，围绕磁畴动力学与相变进行深入研究。实现了准确分析真实磁畴状态、定性分析各类磁畴壁，发现了前人未报道过的金属材料涡旋磁结构在限域空间中以新颖的单链形式集体运动，给出了合金条带的“宽度-温度”磁化相图。研究了磁性核壳材料等铁磁材料的超显微结构与性质，如剩余磁化强度、“核、壳、界面”等区域的过渡族元素的自旋电子状态。发表SCI论文52篇，含自然通讯1篇、美国科学院院刊1篇、先进材料2篇。