Dynamics of a magnetic skyrmionium driven by a spin wave.

Among the many magnetic objects for next generation storage technologies, the skyrmion has drawn the most attention and commentary due to its nanometric size and topologically protected stability [1]. However, the application of skyrmion motion along the nanotrack whether driven by spin-polarized electric current or a spin wave, would both face a significant obstacle, that is “Hall behavior” accompanied by a topological number of $\mathrm {Q}= +1$ [2, 3]. To overcome this problem, skyrmionium emerged as intriguing resolution with zero topological number and skyrmion-like structure, shows great promise for use in magnetic and spintronic applications because it does not suffer from the skyrmion Hall effect. It has been first observed on a ferrimagnetic film in the experiment of laser radiation [4]and can be moved and manipulated by spin current [2]. So far how skyrmionium driven by magnon current has not been investigated. Therefore, in this paper, we study in detail the dynamics of skyrmionium driven by a spin wave in chiral magnetic film and nanotrack. Figure 1 shows snapshots of spin-wave-driven motion process of three magnetic objects, which display significant differences when responding to a magnon current, behaving in not just the motion directions but velocities. Then we proceed an effective analysis in the framework of Thiele equation [5] to explain why skyrmionium is moving along the direction of magnon current, contrary to skyrmion. We find that the transverse component of velocity is attributed to the longitudinal scattering section of skyrmionium. Afterwards in order to explore the potential of spin waves-driven skyrmionium in future spintronics application, we further investigate the related factors influencing the skyrmionium motion in a nanotrack, including the nanotrack width, the Gilbert damping, the inner and outer radius of skyrmionium. Figure 2 presents the dependence of velocity of the skymionium on perpendicular magnetic field by changing the radius of skyrmionium in the nanotrack. Finally, we research the status of skyrmionium after stopping spin wave. In conclusion, we demonstrate that the skyrmionium not only does not have Hall behavior but also move along the magnon current, which is distinctly different from the skyrmion. Most importantly, the velocity of skyrmionium is lager than skyrmion in driving of the magnon pressure and can be effectively tuned by small magnetic field. Our results provide a base for applying magnon-driven skyrmionium in novel information storage and spintronics devices.