Topological spin structures beyond skyrmions from first-principles

磁性天子子--稳定的局域自旋结构--为未来的自旋电子应用带来了巨大的希望。它们在自旋电子器件中潜在应用的一个关键限制是天空粒子的霍尔效应，它导致天空粒子偏离电流方向。因此，在类似于赛道的几何形状中，天空中的天子向轨道的边缘移动，导致它们的湮灭，从而丢失信息。在使用天空微子作为信息载体方面，也阻碍了比特只能通过天空微子的存在(=1)或不存在(=0)来存储。非常希望有另一种可以充当零比特值的亚稳自旋结构。因此，研究一种以上亚稳自旋结构可以共存的系统，不仅从基本的角度来看是很有趣的。已经预言了一个超越Skyrmions的拓扑自旋结构的动物园，例如反Skyrmions、反铁磁Skyrmions或更高阶Skyrmions。这些自旋结构表现出很有前途的性质，最显著的是由于没有天空米子霍尔效应而改善了控制。然而，大多数的理论研究都是基于具有任意磁相互作用参数的自旋模型，并且这些自旋结构的稳定性在很大程度上还没有被探索。特别是，坍塌机制尚不清楚，保护它们免遭湮灭的能量屏障也没有计算出来。最终，这种拓扑自旋结构的寿命需要确定，这是一项非常具有挑战性的任务，因为可能的跃迁路径很复杂，而且不仅需要计算能垒，还需要计算Arrhenius定律的尝试频率。我们还迫切需要第一性原理计算和原子自旋模拟相结合的方法来探索Skyrmions以外的拓扑自旋结构的性质，并预测它们的发现和潜在的应用前景。在这个项目中，我们将利用密度泛函理论(DFT)开发和应用一个建立在第一性原理电子结构理论基础上的原子自旋模拟程序来预测表现出Skyrmions以外拓扑自旋结构的新型磁性界面。使用尖端的原子自旋模拟--它在这个项目中进一步发展，使它们可以应用于Skyrmions以外的拓扑自旋结构--我们将基于所有磁相互作用的DFT参数，探索它们的性质，如坍塌和产生机制，它们的稳定性和在有限温度下的寿命。系统的选择是这样的，它们在实验上是可行的，这可能允许发现Skyrmions以外的拓扑自旋结构并实验研究它们的性质。这将是在自旋电子器件中使用这种自旋结构的重要一步。

Magnetic skyrmions – stable, localized spin structures – hold great promise for future spintronic applications. A key limitation of their potential application in spintronic devices is the skyrmion Hall effect which leads to a deflection of skyrmions from the direction of the electric current. Therefore, skyrmions in a race-track like geometry move towards the edge of the track resulting in their annihilation and thus the loss of information. In terms of using skyrmions as information carriers it is also hindering that the bit can only be stored by the presence (=1) or absence (=0) of the skyrmion. It is highly desirable to have another kind of metastable spin structure which can act as the zero bit value. Therefore, it is not only interesting from the fundamental point of view to study systems in which more than one type of metastable spin structure can co-exist. A zoo of topological spin structures beyond skyrmions, e.g. antiskyrmions, antiferromagnetic skyrmions or higher-order skyrmions, has been predicted. These spin structures exhibit promising properties most prominently improved control due to the absence of the skyrmion Hall effect. However, most of the theoretical studies are based on spin models with arbitrary magnetic interaction parameters and the stability of these spin structures remains largely unexplored. In particular, the collapse mechanisms are unknown and the energy barriers protecting them against annihilation have not been calculated. Ultimately, the lifetime of such topological spin structures needs to be determined which is a very challenging task due to the complexity of possible transition paths and the need to calculate not only energy barriers but also the attempt frequencies of the Arrhenius law. There is also a strong need for first-principles calculations in combination with atomistic spin simulations to explore the properties of topological spin structures beyond skyrmions and to predict promising material systems for their discovery and for potential applications.In this project, we will develop and apply an atomistic spin simulations code built on first-principles electronic structure theory using density functional theory (DFT) to predict novel magnetic interfaces exhibiting topological spin structures beyond skyrmions. Using cutting-edge atomistic spin simulations – which are further developed within this project such that they can be applied to topological spin structures beyond skyrmions – we will explore their properties such as collapse and creation mechanisms, their stability and their lifetime at finite temperature based on DFT parameters for all magnetic interactions. The choice of systems is such that they are experimentally feasible which may allow to discover topological spin structures beyond skyrmions and to experimentally investigate their properties. This will be an important step towards using such spin structures in spintronic devices.