Ab initio investigation of the role of the bridging atoms to the spin transferability between magnetic centrers

在磁盘逐渐被非磁性信息存储方式（闪存、固态磁盘、SSD）所取代的同时，人们也在努力用磁性部件取代其他传统上非磁性的计算机部件。与此同时，将（电子）电路小型化到原子水平已成为最理想的工业目标。这两个原因结合在一起，导致了自旋电子器件和纳米结构磁态相干操纵的理论和实验研究的增加。当前项目头两年的目标是研究相邻磁中心（这里是Fe， Co， Ni原子）的电子桥接如何影响自旋可转移性，从而影响多中心磁性分子的逻辑功能可操作性。这包括研究自旋转移作为化学性质（金属丰度）的函数，桥接原子的数量，自旋和电荷极化。在追求这些目标的过程中，我们推导出了几个自旋翻转和自旋转移的机制，以及许多控制它们的一般规则。然而，这些一般规则似乎主要依赖于几何基础，而不是桥原子的化学性质。目前我们了解到，一个星团的对称性需要足够低，初始/最终态和中间态之间的能量差必须足够高，才能保证一个成功的λ过程。在调查过程中，我们又获得了一些显著的结果。详细地说，我们发现一个重要的机制是声子-自旋耦合，它作为我们的光驱动过程的介质。这激发了更详细的研究：(i)桥接原子的金属丰度，（ii）声子-自旋耦合的影响，（iii）电子态对间接声子-自旋耦合的作用，以及（iv）含声子的CO对自旋动力学过程的影响。进一步阐明这些机制将有助于有针对性地设计更成功的纳米结构，从而极大地促进功能性纳米级磁性器件的发展。

While magnetic disks are gradually being replaced by nonmagnetic means of storing information (flash rams, solid state disks, SSD) there is an ongoing strive to replace other computer parts, traditionally nonmagnetic, by magnetic counterparts. At the same time the miniaturization of (electronic) circuits down to an atomic level has become a most desirable industrial goal. These two reasons combined have led to an increase of both the theoretical and experimental investigation of spintronic devices and coherent manipulation of the magnetic state of nanostructures.The goals of the first two-year period of the current project were to investigate how the electronic bridging of adjacent magnetic centers (here Fe, Co, Ni atoms) affects the spin transferability and thus the logic functional operability of multicenter magnetic molecules. This included the investigation of spin transfer as a function of the chemical nature (metallicity), the number, and the spin and charge polarization of the bridging atoms.When pursuing those goals we derived several mechanisms both for spin flip and for spin transfer, as well as many general rules which govern them. However, these general rules seem to rely mostly on geometrical grounds instead of the chemical nature of the bridge atoms. At present we understand that the symmetry of a cluster needs to be sufficiently low and the energetic difference between initial/final state and intermediate state(s) has to be sufficient high to ensure a successful Lambda-process. During the investigation we came to some additional remarkable results. In detail we have found that a substantial mechanism is the phonon-spin coupling which acts as a mediator for our optically driven processes. This motivates the more detailed study of (i) the role metallicity of the bridging atoms, (ii) the effect of phonon-spin coupling, (iii) the role of the electronic states on the indirect phonon-spin coupling, and (iv) the effect of CO including phonons on the spin dynamic processes.Elucidating further those mechanisms will ease the targeted designing of even more successful nanostructures, and thus substantially contribute to the development of functional, nanoscale magnetic devices.