Topological spin structures beyond skyrmions from first-principles

• Applicant: Professor Dr. Stefan Heinze
• Subject Area: Theoretical Condensed Matter Physics ; Experimental Condensed Matter Physics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 462602351

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.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2137: Skyrmionics: Topological Spin Phenomena in Real-Space for Applications
• International Connection: Iceland
• Cooperation Partner: Professor Dr. Pavel Bessarab