ABSTRACT
Helimagnetic NWs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 7 .3 .3 Edge-Mediated Skyrmion Chain and Its Dynamics
in Nanostripes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
7 .4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
7 .1 Introduction Traditional magnetic storage in hard disk drive technology is based on the controllable manipulation of magnetic domains by a magnetic field. Magnetic recording devices require high coercivity materials to insure thermal stability at high storage densities. However, the requirements of small volume (for high densities), low coercivity (for good writeability), and high thermal stability cannot be optimized at the same time. The capacity of the conventional hard disk storage is thus almost approaching its limit [1]. The emergence of topological phenomena and topological materials offers immense opportunity to extend the storage device roadmap [2-5]. In magnetic materials, a notable example of a topologically stable object is the skyrmion, a swirl-like spin texture that is characterized by all the magnetic moments pointing in all directions wrapping a unit sphere. The peculiar twists of the magnetization within the skyrmion enable efficient couplings within the spin current, leading to topological Hall effects, and strong spin-transfer torque effects [6,7]. Accordingly, the critical current density to move skyrmions is several orders of magnitude lower than that needed to drive ferromagnetic domain walls [8-10]. Meanwhile, the size of a single skyrmion is typically on the order of 5-100 nm and can be continuously tuned by doping [11]. This high mobility, small size, and topological stability are all advantages to building skyrmion-based memory or logical devices, wherein the designs are all based on the formation and controlled manipulations of the spin textures in magnetic nanostructured elements [12]. It is therefore an important issue to understand the formation and stability of skyrmions in highly confined geometries.
