Atomistic Simulations on Dynamics of a Magnetic Skyrmion: Role of Atomic Defects in the Breathing Mode

Abstract

Owing to the fascinating properties of the magnetic skyrmion such as topological robustness, high density, and high energy efficiency [1], it has been considered as one of the prominent candidates for future spintronic devices. It has been known that the magnetic skyrmions are topologically protected, however, it has intrinsically atomistic nature: this topological spin structure formed physically on the atomic sites in monolayer-scaled-thickness thin films. Consequently, it is inevitably influenced by the interfacial roughness and the thermal fluctuation. To study such atomistic effects on the skyrmion, a numerical method based on the atomic scale micromagnetic model is necessary. In this work, we observe effects of atomic defects on dynamics of the skyrmion, the breathing modes, by atomistic micromagnetic simulations [2]. As a model system, monolayers Co nanodisk with 60 nm diameter was used. We assumed that the Co film has simple cubic (SC) structure with the lattice constant of 2.5 Å and the interfacial Dzyaloshinskii-Moriya interaction (DMI) appears only at the bottom surface [3][4]. The DMI is considered as the tensor form of magnetic interaction between neighbor spins. The randomly formed vacancies on the surface showed the roughness of the interface as shown in Fig. 1(a). As shown in Fig. 1 (b), the breathing modes varies dramatically with the roughness. Furthermore, we found that the stable size of the skyrmion affected sensitively by the roughness.