Experimental Realization of skyrmions and vortices on 3D curvilinear surfaces

Abstract

Magnetic materials have been investigated intensively on two-dimensional substrates and planar thin films. Based on the intrinsic interactions, magnetic vortices can be stable nonuniform textures in systems lacking a perpendicular magnetic anisotropy [1]. If the system is pushed more out-of-plane due to the additional anisotropy, magnetic skyrmions can also form when a symmetry-breaking energy is introduced by Dzyaloshinskii-Moriya interactions [2]. These objects can be excited using microwave fields, which result in either their gyromotion or breathing modes, as observed in two-dimensional systems [3]. In a series of works, we demonstrate that we can use a combination of polystyrene spheres and magnetron sputtering to experimentally realize isolated skyrmions and arrays of vortices on three-dimensional curvilinear surfaces; see Fig. 1. We show that skyrmions can be stabilized when imaged with a standard magnetic force microscope. Here, the stray field of the tip is crucial in breaking down the domains and generating the skyrmions at the apex of the spheres. Furthermore, we show that when using NiFe, magnetic vortices can be stabilized on these spheres, which were experimentally realized decades ago [4]. As a novelty, we employ time-resolved scanning transmission X-ray microscopy to directly observe the gyromotion and higher frequency modes of magnetic vortices. Fig. 1: (a) Schematic illustration of the monolayer of polystherene spheres with a diameter of 919 nm and the corresponding atomic force microscopy image in (b). When Pt/Co/Ta multilayers are sputtered on top of the spheres, we observe in (c) the formation of isolated skyrmion at the center of the spheres. Magnetic in-plane vortices are depicted on the spheres using scanning X-ray transmission microscopy. References [1] T. Shinjo, et al., Science 289.5481, 930-932 (2000). [2] Y. Tokura,. Kanazawa. Chemical Reviews 121.5, 2857-2897 (2020). [3] B. Satywali, et al., Nature Communications 12.1, 1909 (2021). [4] R. Streubel, et al., Physical Review B 85.17, 174429 (2012).