Structure and magnetism of cluster ensembles on metal surfaces: Microscopic theory of the fundamental interactions

结合第一性原理和模型量子理论，研究了贵金属表面相互作用的三维过渡金属团簇的结构和磁性。在格林函数Korringa-Kohn-Rostoker(GF-KKR)密度泛函理论(DFT)的框架下，确定了基片介导的团簇结合能和团簇间的磁耦合。自旋-轨道相互作用和非共线磁序的影响是在自洽紧束缚理论框架下确定的。作为实验上相关参数的函数进行系统研究，例如颗粒大小N(例如，FeN、CoN和CrN)、衬底类型(例如，不同的铜、银和金表面)、团簇间距离、团簇的相对取向(结构和磁性)以及表面覆盖率。特别关注量子电子结构效应，特别是在小尺寸的不可伸缩区域。为了确定纳米结构中的结构驰豫，在从头算GFKKR计算的基础上，推导了简单的有效团簇相互作用模型。对于优化的几何构型，确定了相互作用团簇的基本磁性，如自旋磁矩和轨道磁矩、可能的复数非共线磁序和磁各向异性能量。详细分析了相互作用和弛豫对磁性的影响。将结果与目前的实验(如STM、STS、MOKE和XMCD)进行了比较。目前互补的理论工具的组合旨在实现对表面团簇相互作用的微观理解，并有助于改进具有定制磁性的新团簇材料的设计。

The structural and magnetic properties of interacting 3d transition-metal clusters on noble-metal surfaces are investigated by combining first-principles and model quantum theory. The substrate-mediated binding energies and magnetic couplings between clusters are determined in the framework of the Green’s functions Korringa-Kohn-Rostoker (GF-KKR) approach to density-functional theory (DFT). The effects of spin-orbit interactions and noncollinear magnetic order are determined in the framework of selfconsistent tight-binding theory. A systematic study is performed as a function of experimentally relevant parameters such as particle size N (e.g., FeN, CoN, and CrN), type of substrate (e.g., different Cu, Ag and Au surfaces), intercluster distance, relative orientation of the clusters (both structural and magnetic), and surface coverage. Special attention is paid to quantum electronic-structure effects, particularly in the small-size nonscalable regime. Simple effective cluster-interaction models are derived on the basis of the ab initio GFKKR calculations in order to determine the structural relaxation in the nanostructure. The fundamental magnetic properties of interacting clusters, such as the spin and orbital magnetic moments, possible complex noncollinear magnetic orders, and magnetic anisotropy energy are determined for the optimized geometries. The effects of interactions and relaxation on the magnetic properties are analyzed in detail. The results are compared with current experiments (e.g., STM, STS, MOKE and XMCD). The present combination of complementary theoretical tools aims to achieve a microscopic understanding of cluster interactions at surfaces and contribute to refine the design of new cluster materials with tailored magnetic properties.