衬底负载稀土金属原子/团簇/超原子的构筑及单轴磁各向异性调控

The ultimate limit of classical data storage is a single-atom magnetic bit, and it is a long-term and ultimate goal of the superhigh density magnetic data storage. Concerning the recently scientific breakthroughs toward the single-atom magnets [Nature 503, 242 (2013); Science 344, 988(2014); Science 352, 318(2016); Nature 543, 226 (2017)], this project will devote to promoting the magnetic anisotropy energy (MAE) of the nanomagnets (adatom/cluster/superatom) in order to resolve the bottleneck problem, i.e., the reduction of magnetic stability of nanomagnet at the atomic scale. By means of the global search methods of the lowest energy structure, together with the first-principle density functional theory (DFT) and tight-binding approach (TB) methods including the spin-orbit coupling (SOC), free-standing lanthanide metal clusters and superatoms (such as Pr, Ho, SmCo, NdFe clusters; Na12Ln superatom) would be studied systematically to gain their geometrical structures, electronic structures, magnetic moments, as well as the MAEs. Then, the optimal lanthanide magnets would be selected and deposited on different substrate surfaces, after which the adsorption stability, spin and orbital magnetic moments, and MAEs will be calculated. By choosing the magnets size and composition, optimizing the magnet and substrate combinations, or coating the organic molecules on magnet, we want to obtain the substrate-supported magnets with high adsorption stability, large magnetic moment and high uniaxial perpendiucular MAE. On the basis of successfully interpreting the experimental measurements and revealing the underling mechanism, it is helpful to extract the general rules and effective method for regulating the magnetic moment and MAE. This project can not only provide theoretical support for the development of the novel magnets and their future applications in spintronic device and high-density magnetic recoding media, but also push forward the academic innovations in the fields of cluster science and magnetism.

基于磁存储材料的重大应用需求和单原子磁存储技术的重大科学突破[Nature 503, 242(2013); Science 344, 988(2014); Science 352, 318(2016); Nature 543, 226(2017)]，项目致力于提升原子尺度纳米磁体的磁各向异性能(MAE)以解决制约其应用的瓶颈问题—磁稳定性减弱。结合密度泛函理论、分子动力学及高通量结构搜索等理论方法，筛选性能优异的稀土金属原子/团簇/超原子并将其沉积于多种类型衬底表面，通过磁体微观结构设计、磁体-衬底优化组合、有机分子吸附等调控手段，掌握磁性和MAE调控的普适性规律和方法。在解释近期实验并揭示物理机理的基础上，构建出稳定性好、磁矩大、MAE值高、磁化方向垂直于衬底表面的稀土金属纳米磁体，为新型超高密度磁存储材料和自旋电子学器件的研发提供理论支撑，推动我国团簇物理学和磁学领域的交叉融合。

衬底支撑的稀土金属原子/团簇/超原子作为超低维纳米结构体系，其在探究经典超高密度磁储存极限、实现单原子bit位储存、量子计算方面等提供了良好研究对象，并有望发展成为新型高密度储存的磁记录材料。项目聚焦于稀土金属单原子和团簇的磁性和磁各向异性实验测量，利用自旋-轨道耦合第一性原理计算、分子动力学、蒙特卡洛模拟、晶体场模型等理论方法，研究了自由稀土金属Pr团簇，整个稀土周期的单原子以及稀土Sm、Gd、Er等小团簇在不同沉积表面(本征孔状C3N4、金属表面及其支撑绝缘层、单层h-BN表面)的吸附或沉积，系统地考察了低能结构的热力学稳定性、动力学稳定性等方法掌握了稀土金属的成键特征与吸附位点规律，探究了相关体系的磁矩、磁各向异性能、长程磁交换耦合等磁性质关键参量，揭示了支撑衬底对沉积团簇和沉积原子磁各向异性的调控机理，在解释了部分已有的实验数据的基础上预测了系列性能优异的原子磁体；基于性能优异的二维本征磁性材料构建了磁性隧道结，研究了自旋过滤效应、磁电阻效应等自旋输运性质，为稀土材料在自旋电子学器件材料中的应用提供了前期研究基础。通过项目研究，我们获得了如Pr/Nd/Ho原子沉积于C3N4表面、Sm13沉积摩尔表面、Gd团簇沉积h-BN表面、Ce沉积MgO表面等结构稳定性好、饱和磁化强度大、各向异性大、居里温度高的稀土单原子和团簇沉积体系，总结出了沉积团簇的设计步骤和普适性方法，揭示沉积结构—电子结构—磁学性能之间的关系，从电子结构层面理解团簇材料优异磁性能来源的微观机理，从而达到从理论和实验两个角度来掌握它们结构生长和磁特性规律。特别是，我们发现可以通过摩尔衬底表面调控、团簇-界面间的成键和磁耦合等方式，可控性地调节体系整体的饱和磁化强度和磁各向异性，为进一步的实验开展提供了坚实的理论基础。