间隔层调控的各向异性软/硬磁纳米复合多层膜的磁性和层间耦合机制研究

Spacered soft/hard-magnetic nanocomposite films will be prepared by magnetron sputtering. By tuning sputtering pressure, deposition temperature and ratios, microstructure and morphology as well as the magnetic domains of films will be studied. Their relationship with magnetic properties will be established. At the interface region between soft/hard-magnetic layers, the composition and local microstructure will be compared with and without spacer layer. In the nanocomposite films with spacer layers of fixed thickness, magnetic parameters, such as magnetocrystalline anisotropy and saturation magnetizations, and microstructural parameters, such as interface roughness and grain sizes, will influence the coercivity, squareness and demagnetization process. Their inter-relationship will be established. The effects of spacer layer thickness on the coercivities, squareness and demagnetization process will be studied. The quantitative dependence of exchange coupling stiffness on the thickness of spacer layer will be tentatively established. Based on the experimental results, micromagnetic models will be founded to contribute the theory of anisotropic exchange coupling and guide the development of nanocomposite magnets.

采用磁控溅射方法制备具有间隔层的软/硬磁纳米复合磁性薄膜。通过调整溅射气压、沉积温度和速率等参数调节微观结构和形貌，研究相应的磁畴结构的变化，并建立起这些因素与薄膜磁性变化的关系。通过在软/硬磁界面处引入间隔层，研究界面处结构和成分的变化。在固定间隔层厚度时，研究软硬磁层的磁晶各向异性和磁化强度等磁性参量、界面粗糙度和晶粒尺寸等微观组织对纳米复合磁性薄膜的矫顽力、矩形度和退磁过程的影响。通过改变间隔层的厚度，考察复合薄膜矫顽力、矩形度和退磁过程的变化，探索层间耦合的变化趋势并建立起定量关系。在归纳总结实验结果的基础上，构建微磁学模型，丰富各向异性交换耦合理论并为发展纳米复合永磁体提供指导。

理论预言，在纳米复合磁体中，利用硬磁相高矫顽力、软磁相高饱磁及软硬磁之间的交换耦合可以获得更高的性能。实验上，我们通过在界面处插入非磁Ta层调控耦合并修饰界面，已经获得了超高磁能积与良好的晶各向异性。非磁间隔层的作用及相间耦合强度的变化还不清楚，因而在本项目中，通过回复曲线、微磁学模拟计算，在不断增厚间隔层Pt厚度的FePt/Pt/Fe三层膜中，系统研究了交换耦合劲度系数的变化；同时，通过界面外延生长，调控垂直取向的SmCo硬磁相的矫顽力及退磁耦合，进而研究了晶粒形貌对矫顽力热稳定性的影响；由于磁性原子间的交换耦合对原子间距非常敏感，因而在MnxGa体系中，我们通过施加原位应力于具有L10和D022两种晶体结构的MnxGa相。实验发现，具有D022相MnxGa在应力下矫顽力增大，同时交换耦合作用增强，而L10相MnxGa合金的磁滞回线在零场附近出现kink，这说明其磁晶各向异性变弱，并导致静磁耦合变强；第一性原理计算进一步表明，磁晶各向异性的变化来源于Mn原子dz2轨道间耦合相互作用的变化。由于矫顽力是微观结构因素，因而通过扩散处理改善晶界、相成分及其分布会显著影响矫顽力，我们采用Nd-Co、Dy-Cu处理Nd-Fe-B及Nd-Cu、Nd-Ag处理Nd-Ce-Fe-B都提高了矫顽力，并改善了矫顽力温度系数，验证了预期结果。