各向异性硬磁/软磁纳米颗粒多层自组装阵列的交换耦合机制和磁性研究

In order to accurately control exchange coupling in nanoscale, anisotropic hard magnetic/soft magnetic nanoparticles (NPs) multilayer self-assembly arrays will be prepared through chemical synthesis and self-assembly methods. Influences of size, magnetocrystalline anisotropy, shape anisotropy and domain structure of hard magnetic NPs, size, materials and morphology of soft magnetic NPs, interface structure and orientation of easy axis on short range direct exchange coupling will be investigated. Spacer layer will be coated on the surface of hard magnetic NPs. Influences of materials, magnetism and thickness of spacer layer and different hard and soft magnetic structure on long range indirect exchange coupling will be further studied to find the intrinsic relationship between these factors and exchange coupling. Distribution of the magnetic moment of the interface and interlayer in cross section and domain structure in the surface of the samples with different structure will be investigated by changing temperature and external magnetic field, to further find out the regularity and the effects of these conditions on magnetic properties and exchange coupling. The micromagnetic simulation will be used to develop the theoretical models of short range direct and long range indirect exchange coupling of anisotropic hard magnetic/soft magnetic NPs multilayer self-assembly arrays. Combined the experimental results and the theoretical models, the optimal microstructure of nanocomposite permanent magnets with high energy product will be discussed, which will offer a role of guidance for the development of nanocomposite permanent magnets.

采用化学法和自组装技术制备各向异性硬磁/软磁纳米颗粒交换耦合多层自组装阵列，在纳米尺度对交换耦合进行精确调控。系统研究硬磁纳米颗粒的尺寸、磁晶各向异性、形状各向异性、畴结构、软磁纳米颗粒的尺寸、种类和形貌、硬磁和软磁相界面结构及易磁化轴取向对近程直接交换耦合的影响；在此基础上，在硬磁纳米颗粒表面包覆隔离层，进一步研究隔离层的材料、磁性、厚度、不同硬磁软磁结构等因素对长程间接交换耦合的影响，从而找出这些因素与长程间接交换耦合的内在关系。研究不同温度和磁场下不同结构多层自组装阵列横断面和平面的静态和动态磁畴结构及磁距分布，找出对交换耦合机制和磁性能影响的内在机理。利用微磁学模拟完善各向异性硬磁/软磁纳米颗粒多层自组装阵列这一新颖模型的近程直接、长程间接交换耦合的理论模型。结合实验结果和理论模型，探讨获得高最大磁能积纳米复合永磁材料的最佳微观结构，对进一步发展纳米复合永磁材料提供有效指导。

永磁材料是工业和国防等领域的基础性关键功能材料，然而传统单相永磁材料已很难满足社会对高磁能积永磁材料发展的需要。本项目基于bottom-up方法开展了硬磁软磁交换耦合纳米复合永磁材料的可控制备、磁性能调控和交换耦合机制研究，具体内容为：以液相合成方法为基础，制备了形貌和尺寸可控的单分散L10-FePt纳米晶，提出了卤素诱发硬磁FePt纳米颗粒有序化的生长机制；合成了50-200 nm的单分散SmCo5基纳米晶，利用bottom-up方法制备了各向异性永磁材料，建立了外磁场调控纳米颗粒易磁化轴取向的微观机制；以NbFeB/ MgO/Fe多层薄膜和阵列为模型，阐明了隔离层及软磁相尺寸与硬磁软磁交换耦合作用及磁畴结构和反磁化过程的关联机制；利用LB技术制备了L10-FePt/Fe纳米颗粒自组装阵列，揭示了硬磁相的矫顽力和尺寸及多层膜周期结构对矫顽力、饱和磁化强度及两相相互作用的影响机制；基于自蔓延燃烧方法首次制备了多孔BaFe8Al4O19/Co0.6Zn0.4Fe2O4硬磁软磁交换耦合纳米复合永磁材料，建立了孔结构、软磁相尺寸及比例与磁性能的依赖关系。该项目所取得的研究结果可为完善和发展硬磁软磁交换耦合理论提供更为清晰的科学依据，进而为优化和提高纳米复合永磁材料的最大磁能积提供实验和理论指导。