Skyrmion battery effect via inhomogeneous magnetic anisotropy

Abstract

Magnetic skyrmions are considered as a promising candidate for the next-generation information processing technology. Being topologically robust, magnetic skyrmions are swirling spin textures that can be used in a broad range of applications from memory devices, logic circuits, to neuromorphic computing. In a magnetic medium lacking inversion symmetry, magnetic skyrmion arises as a result of the interplay between magnetic exchange interactions, Dzyaloshinskii-Moriya interaction, and magnetic anisotropy. Instrumental to the integrated skyrmion-based applications are the creation and manipulation of magnetic skyrmions at a designated location, absent any need of a magnetic field. In this paper, we propose a generic design strategy to achieve that and a model system to demonstrate its feasibility. By implementing in a disk-shaped thin film heterostructure an inhomogeneous perpendicular magnetic anisotropy, stable sub-100-nm size skyrmions can be generated without magnetic field. This structure can be etched out via, for example, focused ion beam microscope. Using micromagnetic simulation, we show that such heterostructure not only stabilizes the edge spins of the skyrmion, but also protects its rotation symmetry. Furthermore, we may switch the spin texture between skyrmionic and vortex-like ones by tuning the slope of perpendicular anisotropy using a bias voltage. When embedded into a magnetic conductor and under a spin polarized current, such heterostructure emits skyrmions continuously and may function as a skyrmion source. This unique phenomenon is dubbed as skyrmion battery effect.Our proposal may open a novel venue for the realization of all-electric skyrmion-based device.

Stabilization of skyrmions in two-dimensional systems with next-nearest-neighbor exchange interactions

“…The total energy as a function of exchange interaction J 1 is plotted in Figure 3B in the presence of an isolated meron (black line) and bimerons (red line). The total energy is dominated by the ferromagnetic region and thus decreased when J 1 is increased [26]. The topological number of merons almost remains the same as shown in Figure 3C, while the diameter of merons decreases with the increasing J 1 as shown in Figure 3D.…”

Manipulation of Skyrmion Motion Dynamics for Logical Device Application Mediated by Inhomogeneous Magnetic Anisotropy

“…From the simulation results and analyses above, one may tailor the skyrmion structure on demand by introducing different energy potential wells or energy potential barriers into the nanostructure via the inhomogeneous PMA distribution. To preserve the rotational symmetry of skyrmion, many studies focused on isolated skyrmions confined in circular nanodisks [8,13], and it was demonstrated that the isolated skyrmions can be stabilized by using inhomogeneous PMA in disk-shaped heterostructure with circle-shaped capping layer [30]. In the simulations, we found that isolated skyrmions can be generated and stabilized in the proposed heterostructures with square-shaped or circle-shaped capping nano-islands.…”

“…In this work, we studied the manipulation of skyrmion mediated by local inhomogeneous PMA in the heterostructures. We proposed an architecture of a capping nano-island fabricated on the top surface of an ultrathin Co/Pt film, in which the PMA strength (K c ) of capping island (Region II) can be largely modified by different capping materials [28][29][30], as schematically shown in Figure 1a. Here, the desired K c can be manufactured by choosing a proper capping material with modified material parameters, e.g., strain and sample thickness.…”

“…So far, most of the investigations regarding the effects of PMA on skyrmions focused on homogenous PMA systems. Recently, inhomogeneous PMA introduced by using capping layer [28][29][30] or a voltage-controlled magnetic anisotropy (VCMA) gate [31] has also attracted more and more interests. Such a nonuniform PMA can serve as potential well or barriers to control the local dynamic behavior of skyrmion, e.g., pinning or depinning of skyrmion, which shows promising features for applications in skyrmion transistors, memories, logic gates, etc.…”

“…Such a nonuniform PMA can serve as potential well or barriers to control the local dynamic behavior of skyrmion, e.g., pinning or depinning of skyrmion, which shows promising features for applications in skyrmion transistors, memories, logic gates, etc. [30,[32][33][34][35][36][37]. To explore the intriguing magnetic devices for multifunctional logic applications, most investigations were carried out in the multi-channel and multi-network circuits [34][35][36][37].…”