G.P. Zhao

All-magnetic control of skyrmions in nanowire by spin wave

A skyrmion is a topological particle-like excitation in classical continuum field theory [1-3]. Skyr-mion can be driven by spin-polarized current [4, 5]. However, to move the skyrmion along the central line of a nanotrack by in-plane spin-polarized current requires severe matching between the damping coefficient and the non-adiabatic coefficient, i.e. α is close to β, limiting possible material systems for skyrmion applications [5-7]. Another possibility of controlling a skyrmion is to use spin wave. Spin wave produces less heat than electric current, which therefore is promising for practical applications. We investigate the skyrmion dynamics driven by spin wave in constricted geometries with the Dzyaloshinskii-Moriya interaction (DMI) such as nanotracks, L-corners, T- and Y-junctions, which are the basic ingredients of circuits based on skyrmions.

Magnetic Skyrmion Transport in a Nanotrack With Spatially Varying Damping and Non-Adiabatic Torque

Reliable transport of magnetic skyrmions is required for any future skyrmion-based information processing devices. Here, we present a micromagnetic study of the in-plane current-driven motion of a skyrmion in a ferromagnetic nanotrack with spatially sinusoidally varying Gilbert damping and/or non-adiabatic spin-transfer torque (STT) coefficients. It is found that the skyrmion moves in a sinusoidal pattern as a result of the spatially varying Gilbert damping and/or non-adiabatic STT in the nanotrack, which could prevent the destruction of the skyrmion caused by the skyrmion Hall effect. The results provide a guide for designing and developing the skyrmion transport channel in skyrmion-based spintronic applications.

Skyrmion state of exchange coupled core-shell nanostructure

The intriguing magnetic states - skyrmion and skyrmion lattice - have been observed and created in helical magnetics, such as MnSi, Fe1-xCoxSi, the helical FeGe and monolayer Fe film [1-3]. The skyrmions in helical magnets are always associated with the chiral magnetic interaction, namely Dzyaloshinskii-Moriya interaction (DMI). However, several novel works present new approaches to create the skyrmion in nanostructures in absence of DMI [4-7]. Here, we study the skyrmion created in exchange coupled core-shell structure (Co/CoPt) without DMI. As shown in Fig. 1, exchange coupled core-shell disk and square has been modeled under the framework of micromagnetics. For the core-shell nanodisk, r represents the radius of core region, and R represents the radius of the whole nanodisk. Similarly, l represents the edge length of the core region and L represents the edge length of the whole nanosquare. t represents the thickness of the disk as well as nanosquare.

Voltage-gated skyrmion transistor

Magnetic chiral skyrmions are localized topological field configurations, which are stabilized by Dzyaloshinskii-Moriya interaction and/or magnetostatic dipolar coupling in magnetic nanostructures. To realize and eventually commercialize skymionics, various challenges need to be solved such as creating and annihilation of skyrmions, conversion of skyrmions with different helicity and vorticity, efficient transmission and read-out of skyrmions, etc. This work addressed the critical problem of voltage control of magnetic skyrmion, in which the perpendicular magnetic anisotropy (PMA) in the gate region is locally controlled by an applied electric field due to the charge accumulations. With the configuration of applying a gate voltage in the center region of a magnetic nanotrack, two prototypes of transistors have been investigated: skyrmion driven by spin current and skyrmion driven by spin wave.

Skyrmion Spin Structure of Exchange-Coupled Magnetic Core–Shell Nanodisk

We study the skyrmion spin texture created in a cylindrical exchange-coupled magnetic core-shell nanodisk (Co/CoPt) in the absence of the Dzyaloshinskii-Moriya interaction. The evolution of the skyrmion spin texture under varying applied field is investigated. The skyrmion core size can be tuned by an external magnetic field. However, skyrmion spin texture will be destroyed for a large enough applied field. With the stability and controllability of magnetic states, the exchange-coupled magnetic core-shell nanodisk can make a high potential for future storage media and devices, with the storage of data in the form of skyrmions.