Exchange interactions and spin switching at the single atom level

单原子水平上的交换相互作用和自旋转换

• 批准号: 445697818
• 负责人: Professor Dr. Stefan Heinze
• 金额: --
• 依托单位: Institute for Molecules and Materials
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/445697818?language=en
• 关键词: Exchange; interactions; spin; switching; single

The exchange interaction is of fundamental importance in the theory of magnetism. Typically, its strength – expressed within the Heisenberg model in terms of exchange constants – is determined indirectly in experiments by measuring the effect of inelastic spin excitations for example by neutrons or electrons. It is also possible to probe the exchange interaction directly in the setup of an atomic force microscope (AFM) equipped with a magnetic tip. This technique, which has been first demonstrated in 2007, is coined magnetic exchange force microscopy. It has been used to obtain the exchange interaction between a magnetic tip and magnetic surfaces. However, it has so far not been possible to directly probe the exchange interaction with single adatoms or molecules. On the other hand, contact measurements of single adatoms with the tip of a scanning tunneling microscope (STM) have been performed by various groups. Very recently, it has been demonstrated that one can combine an STM and an AFM using magnetic tips in order to simultaneously measure the spin-polarized (SP) tunneling current and the exchange (EX) interaction – a technique which is known as SPEX imaging and spectroscopy.In this proposed project we aim to understand and guide experiments performed using the SPEX technique by means of density functional theory (DFT) calculations. In the past, DFT has become an indispensable tool to explain scanning tunneling or atomic force microscopy experiments. Here, we will apply DFT to study the exchange interaction between a magnetic tip and magnetic adatoms and dimers on magnetic surfaces. In collaboration with our experimental partners from the Radboud University, Nijmegen, we would like to provide the first exchange energy and force vs. distance curves for single magnetic adatoms. This allows to quantify the exchange constants between the tip apex atom and the adatom and determine its dependence on the chosen adatom and on the tip termination. By obtaining exchange force maps we would also like to gain deeper insight into the exchange coupling mechanisms. A second goal is to demonstrate switching of the spin of a single adatom by exchange forces. We will explore promising systems based on DFT calculations to guide the experimental efforts. Finally, we would like to study the effects of spin-orbit coupling and of noncollinear spin states on the exchange force measurements which have so far not been theoretically explored at all.

交换相互作用在磁学理论中具有根本的重要性。通常情况下，它的强度-在海森堡模型中以交换常数表示-在实验中通过测量非弹性自旋激发（例如中子或电子）的影响来间接确定。它也是可能的探针交换相互作用，直接在设置的原子力显微镜（AFM）配备了一个磁性针尖。这种技术在2007年首次被证明，被称为磁交换力显微镜。它已被用来获得磁尖和磁性表面之间的交换相互作用。然而，到目前为止，还不可能直接探测与单个吸附原子或分子的交换相互作用。另一方面，接触测量的单吸附原子的扫描隧道显微镜（STM）的尖端已进行了各种小组。最近，它已被证明，可以联合收割机STM和AFM使用磁性针尖，以同时测量自旋极化（SP）隧穿电流和交换（EX）interaction -一种技术，这是被称为DAC成像和spectroscopy.In这个拟议的项目，我们的目标是理解和指导使用DAC技术通过密度泛函理论（DFT）计算进行的实验。在过去，DFT已经成为解释扫描隧道或原子力显微镜实验不可或缺的工具。本文利用密度泛函理论研究磁性针尖与磁性吸附原子和磁性表面二聚体之间的交换作用。通过与来自奈梅亨Radboud大学的实验合作伙伴合作，我们希望提供单个磁性吸附原子的第一个交换能量和力与距离的关系曲线。这允许量化尖端顶点原子和吸附原子之间的交换常数，并确定其对所选吸附原子和尖端终止的依赖性。通过获得交换力图，我们还希望更深入地了解交换耦合机制。第二个目标是演示交换力对单个吸附原子自旋的转换。我们将探索基于DFT计算的有前途的系统，以指导实验工作。最后，我们想研究自旋轨道耦合和非共线自旋态对交换力测量的影响，这些影响到目前为止还没有在理论上进行过探讨。