Chengkun Song

Dynamics of antiferromagnetic skyrmion driven by the spin Hall effect

Magnetic skyrmion moved by the spin-Hall effect is promising for the application of the generation racetrack memories. However, the Magnus force causes a deflected motion of skyrmion, which limits its application. Here, we create an antiferromagnetic skyrmion by injecting a spin-polarized pulse in the nanostripe and investigate the spin Hall effect-induced motion of antiferromagnetic skyrmion by micromagnetic simulations. In contrast to ferromagnetic skyrmion, we find that the antiferromagnetic skyrmion has three evident advantages: (i) the minimum driving current density of antiferromagnetic skyrmion is about two orders smaller than the ferromagnetic skyrmion; (ii) the velocity of the antiferromagnetic skyrmion is about 57 times larger than the ferromagnetic skyrmion driven by the same value of current density; (iii) antiferromagnetic skyrmion can be driven by the spin Hall effect without the influence of Magnus force. In addition, antiferromagnetic skyrmion can move around the pinning sites due to its p...

Annealing influence on the exchange stiffness constant of Permalloy films with stripe domains

An investigation of the annealing influence on the stripe domains structure in Permalloy films has been performed by comparing the static and dynamic magnetic properties. An increasing exchange stiffness constant A ex is found when the annealing temperature rises. The magnetic force microscopy images show that the width of stripe domain increases with the increase of annealing temperature, and the increasing exchange stiffness constant is considered to be the most prominent reason. A perpendicular standing spin-wave model is used to deduce the A ex from the evolution of resonance frequencies, and the A ex increases nearly twice from 7.2 × 10−7 ergs cm−1 for the as-deposited film to 12.9 × 10−7 ergs cm−1 for the film annealing at 400 °C. Micromagnetic calculation is also used to compute the magnetization configuration, and the results agree well with the experimental conclusions.

Dynamic response for Dzyaloshinskii-Moriya interaction on bubble-like magnetic solitons driven by spin-polarized current

By using micromagnetic simulations, we studied the dynamic response for different bubble-like magnetic solitons in the [CoPt-CoNi]/Cu/CoNi magnetic multilayer with perpendicular magnetic anisotropy. It is found that a localized spin-polarized current can not only nucleate a dissipative magnetic droplet but also excite the in-plane domain wall (DW) oscillation at the edge of bubble-like magnetic solitons. The dependence of oscillation frequency on current for the dissipative magnetic droplet is hysteretic in the absence of the Dzyaloshinskii–Moriya interactions (DMI). In the presence of DMI, three different bubble-like magnetic solitons are excited: (1) singular magnetic droplet, (2) pseudonormal magnetic droplet, (3) dynamical skyrmion. Meanwhile, the oscillation frequencies of these magnetic solitons have different response as current density varies. These results open up new possibilities for the applications of magnetic soliton-based spin transfer nano-oscillators.

Topological trajectories of a magnetic skyrmion with an in-plane microwave magnetic field

Magnetic skyrmions are stable and topologically protected spin textures which have been observed in several chiral magnetic materials, and the resonant excitations of magnetic skyrmions have become a hot research topic for potential applications in future microwave devices. In this work, we investigate in-plane microwave-induced topological dynamics of a magnetic skyrmion in a nanodisk by using micromagnetic simulations. It is found that the resonant excitations of the skyrmion are elliptical dynamics which contain counterclockwise and clockwise modes by applying different frequencies of the microwave field. The conversion between these two elliptical modes is achieved by a transition to linear vibration. In addition, we demonstrate that the off-centered process of the skyrmion can be controlled by applying different phases of the microwave field. Finally, we discuss the different topological excitations of four types of skyrmions. Our results present the understanding of topological skyrmion dynamics and...

Dynamics of Dzyaloshinskii Domain Walls Driven by Spin Hall Effect in the Presence of Magnetic Fields

Current-induced domain wall motion (CIDWM) in perpendicularly magnetized materials exhibits large potential in spintronic device applications. The Dzyaloshinskii domain walls (DWs) are nucleated in ultrathin ferromagnetic/heavy-metal bilayers with high perpendicular magnetocrystalline anisotropy (PMA) in the presence of interfacial DzyaloshinskiiMoriya interaction (DMI). Here, we investigate the effect of magnetic fields on Dzyaloshinskii DWs driven by spin Hall effect (SHE) by means of micromagnetic simulations. We find that magnetic fields can modify the dynamics of Dzyaloshinskii DW. When applying out-of-plane magnetic fields, the velocity of Dzyaloshinskii DWs increases when the field-driven and current-driven DW motion are in same direction, while it decreases with opposite direction. In the case of in-plane longitudinal magnetic fields, Dzyaloshinskii DW velocity increases when the direction of the magnetic field and Dzyaloshinskii DW propagation direction are same, and it decreases when applying opposite in-plane magnetic fields. These manifestations may offer a new method for manipulating Dzyaloshinskii DWs and promise applications in DW-based nanodevices.

Skyrmion-based multi-channel racetrack

Magnetic skyrmions are promising for the application of racetrack memories, logic gates, and other nano-devices, owing to their topologically protected stability, small size, and low driving current. In this work, we propose a skyrmion-based multi-channel racetrack memory where the skyrmion moves in the selected channel by applying voltage-controlled magnetic anisotropy gates. It is demonstrated numerically that a current-dependent skyrmion Hall effect can be restrained by the additional potential of the voltage-controlled region, and the skyrmion velocity and moving channel in the racetrack can be operated by tuning the voltage-controlled magnetic anisotropy, gate position, and current density. Our results offer a potential application of racetrack memory based on skyrmions.

Current-induced 360° domain wall motion with Dzyaloshinskii–Moriya interaction

By micromagnetic simulation, we investigated the effect of the Dzyaloshinskii–Moriya interaction (DMI) on the static and dynamic characteristics of a 360° domain wall. Simulation results show that both the energy and the size of a 360° domain wall decrease with the increase of DMI intensity. In the presence of DMI, the stable motion of a 360° domain wall can be either along the +x direction or −x direction depending on the sign of the DMI. For stable motion, the maximum velocity of a 360° domain wall is 19.87% larger than that without the DMI. Increasing the current density beyond the Walker threshold, conversion between the 360° domain wall state and the vortex state was observed. Further increasing the current density, the proliferation of 360° domain walls becomes possible. Moreover, the 360° domain wall becomes more flexible and easier to pass a notch by considering the DMI. These findings may offer guidance for the development of 360° domain wall-based racetrack memories.

Effect of perpendicular magnetic field on bubble-like magnetic solitons driven by spin-polarized current with Dzyaloshinskii–Moriya interaction

The topological properties of bubble-like magnetic solitons can be modified by interfacial Dzyaloshinskii-Moriya interaction (DMI). In this paper, the dynamic responses of bubble-like magnetic solitons nucleated in the free layer of the spin-torque nano-oscillators (STNOs) are investigated in the presence of DMI and the perpendicular magnetic field by using micromagnetic simulations. We observed that the oscillation frequency of bubble-like magnetic solitons can be manipulated by the perpendicular magnetic field. Moreover, the magnetic structures keep stable in small DMI. With an increase in the DMI strength, rich kinds of bubble-like magnetic solitons appear at different spin-polarized current and perpendicular magnetic field. These results provide a further understanding of bubble-like magnetic solitons structures and direct applications in STNOs.